Thursday, 27 July 2017

Auto Glossary

An ever expanding list of automotive terms, acronyms, and definitions.



AAA: see American Automobile Association

A-arm: Another name for a control arm because many control arms are shaped like the letter A.

A-Pillar: The roof support on each side of the windshield between the front side windows and the windshield

A-to-D Converter: Analog to digital converter. A module within an electronic control unit that takes an analog input and digitizes the signal for processing in the CPU.

ABCM: Anti-Lock Brake Control Unit, see ABS Module

ABS:  Anti-lock Braking System: A system whereby a computer can apply and release the service brakes of the vehicle very rapidly in order to prevent wheel lock-up. This allows the driver to retain the ability to steer under maximum braking.

ABS Light: A malfunction indicator light for the anti-lock braking system. The light will illuminate to notify the driver that the ABS computer has detected a problem within itself. Also to let the driver know that if the light is on the ABS system might not function properly.

ABS Module: A generic term for the computer control unit in charge of anti-lock brake function. This module is also a node on the vehicle network sharing information with other modules.

Absolute Pressure: A pressure measured from absolute zero as opposed to being measured from ambient conditions.

Absorb: To draw in though the means of capillary action

Absorbed Glass Mat: A type of battery found in cars that contains fiber glass separators between the plates to absorb and hold the battery electrolyte. They are lighter weight, longer lasting, and provide more current for their size than regular lead acid batteries. Deep cycling done not have as much of a harmful effect on them.

A/C: Air conditioning. 2. Alternating current.

ACC: An abbreviation for accessory, usually found as a position on the ignition switch.

A/C Compressor: A pump used to pressurize refrigerant in the air conditioning system in order to allow the refrigerant to move heat out of the passenger area. The compressor is usually belt drive except on hybrid vehicles it has its own internal motor.

A/C Sine Wave: A waveform that can be defined as A/C current switching positive and negative.

Acceleration Squat: The tendency of the rear of a high-power vehicle to squat down over the rear axle as torque is applied and the axle twists. see Axle Tramp

Accelerator:  The control mechanism used by the driver to increase engine speed.

Accelerator Pedal Position Sensor: A sensor attached to the accelerator pedal of any vehicle with drive-by-wire throttle control. These vehicles do not have a cable connecting the gas pedal to the throttle plate. They use this sensor to tell the computer how much throttle the driver is requesting, and the computer opens the throttle actuator accordingly.

Accelerator Pump: A mechanism inside the carburetor that pumps an extra shot of fuel into the intake manifold upon acceleration. This is to prevent a brief lean condition that can cause hesitation. Because this device sprays fuel into the intake anytime the gas pedal is pressed, it also is used to enrichen the air/fuel mixture on start up. This is why pumping the gas pedal helps a cold, carbureted engine start.

Accelerometer: An inertia sensor found in all modern vehicles that can detect changes in motion or direction. These sensors are used for everything from the navigation system to the skid control system.

Accumulator: Any cnaister device in a high-pressure system used to store pressure.

Accumulator, A/C: A canister on the low pressure side of the system that holds liquid refrigerant to prevent it from entering the inlet of the compressor. It also contains a desiccant and a filter screen. An accumulator is usually found on the type of A/C system that use an orifice tube as a metering device.

Acetic Acid: The active ingredient found in RTV sealants that make it liquid enough to apply to mechanical parts. Acetic acid is essentially vinegar, which makes sense because RTV smells a lot like vinegar.

Acetylene: A flammable gas used to create a flame hot enough for heating metal for welding and cutting.

Ackerman Arm: The steering arm attached to or cast as one piece with the knuckle. The end of this arm is where the tie-rod attaches.

Ackerman Principle: The concept that allows toe-out-on-turns due to the angle of the ackerman arm on the steering knuckle.

Active Regeneration: A form of DPF regeneration that is only enabled by a technician using a scan tool to command this process. This regeneration will burn the soot out of the DPF to allow it to keep collecting more particulate matter. An active regeneration becomes necessary when the vehicle is not driven in a manner that allows for passive regeneration. Passive regeneration is what should normally happen to regenerate the DPF.

Active Suspension: A suspension system that is capable of changing its own dynamics automatically to adapt to changing driving or road conditions.

Actuator: A type of motor that converts an electrical signal into mechanical movement in order to perform some kind of function.

Adaptive Memory: The writable memory in an ECU that stores custom programming that results from adaptive strategies used by the ECU.

Adaptive Strategy: Programming in an ECU that allows the computer to adapt it’s control of the system to maintain efficiency despite things like mechanical wear and inefficient users of the vehicle.

Adjustable Wrench: A wrench that has an adjustable opening to allow it to fit on many sizes of fasteners. Usually not as useful as it sounds, and if the bolt is very tight this wrench will only ruin the head so that no wrench will ever fit well enough to loosen the bolt.

Adsorb: To collect or store on the exterior surface and not internally or through capillary action.

Aerobic Sealant: A sealant that requires the presence of oxygen in order to cure.

A/F: air/fuel, as in air fuel ratio

AFR: see Air/Fuel Ratio

AFV: see Alternative Fuel Vehicle, not America’s Funniest Videos

Aftertreatment: Emissions control devices found in the exhaust system of an internal combustion engine which treat the exhaust gases after they have been produced. This term is usually used in reference to diesel powered vehicles. The diesel particulate filter found in the exhaust system is an aftertreatment device.

AGM: see Absorbed Glass Mat

AIR: see Air Injection Reaction

Air Dam: The air diverter built into the front of the car below the front bumper to direct passing air into the radiator, or into the front brake rotors, or over the front of the vehicle to aid in aerodynamic efficiency.

Air Filter: A filter that filters air for the engine. The air filter housing is at the beginning of the intake.

Air/Fuel Ratio: The ratio of air to fuel that is mixed in the cylinder and compressed for combustion. This ratio varies a bit depending on specific engine load. The norml stochiometric AFR is 14.7:1.

Air Injection Reaction: An emission control system that injects air into the exhaust system at each exhaust port, at the end of the exhaust manifold, on at the catalytic converter in order to allow the oxygen in the air to further oxidize HC’s and CO’s that were not fully used up in the combustion process.

Air Suspension: A suspension system that uses air springs instead of metal springs. Air suspension systems are usually capable of varying the ride height of the entire vehicle or just the rear axle for the purposes of load leveling.

Allen Wrench: A wrench used on fasteners with a hexagonal hole in the top. Quite often they are L shaped.

Alternative Fuel Vehicle: A vehicle that runs on a fuel other than gasoline. This may include diesel fuel in the U.S.

Alternator: A device used to generate electricity on-board the vehicle. The alternator is driven via a belt by the engine. The primary jobs of the alternator is to charge the battery and to power electrical accessories while the engine is running.

AMC: see American Motors

American Automobile Association: An organization that provides emergency roadside assistance to motorists who subscribe to their service. They also provide auto insurance and other services for automobile owners.

American Motors Corporation: An American car company that was formed by the merger of Packard and Nash in 1954. In 1970 AMC purchased Jeep from Kaiser. By 1980 AMC was having major financial difficulties and end up selling out to French auto maker Renault. When Renault began having problems a few years later they sold AMC’s remaining assets to Chrysler 1987. The Eagle and Jeep lines survived with Chrysler, but the rest of AMC went defunct in 1988.

American Petroleum Institute: A professional organization made up of petroleum engineers who set refining standards for motor oils.

American Society for Testing and Materials: A non-profit organization that sets standards for many different products. They are the group that sets refinement standards for motor fuels.

American Wire Gauge: A system for indicating the diameter of electrical wires. The smaller the wire gauge number, the larger the diameter.

Ammonia Slip Catalyst: The rear portion of the catalytic converter used in conjunction with SCR systems on modern clean diesel systems. This catalyst will break apart any ammonia that slips through SCR while reducing NOx. The ammonia gets converted to H2O and N2.

Amperage: Amp, Ampere. The unit of current in an electrical circuit. Named for Andre-Marie Ampere, A French physicist who is often considered the father of modern electrodynamics

Anaerobic Sealant: A sealant that requires a lack of oxygen in order to cure.

Analog: Anything infinitely variable within a given range, usually used to describe an electrical signal.

Antifreeze: A chemical mixed with water that comprises the fluid used in the engine cooling system, usually made from ethylene glycol. The fluid in the cooling system must be made to resist freezing in the winter, and resist boiling when the engine is hot. see also Coolant.

Anti-Roll Bar: A suspension component connected to the chassis or frame in the center, and to the axle or other major suspension components on the ends. The bar does not allow full articulation of the suspension when one wheel on the axle goes to the full jounce position, while the other wheel on the axle goes to the full rebound position. This helps the vehicle stay flat when cornering and helps prevent vehicle body roll, or total vehicle roll-over.

Anti-Skid Control: A computer controlled system that can sense when a vehicle is in a skid and can use steering inputs along with braking and throttle action to get the vehicle pointed straight down the road again. Every manufacturer has a different name for this system.

Apex: The point on a line moving through a corner where the line touches the inside of the corner. Used in auto racing to describe the inside of a turn.

API: See American Petroleum Institute

APP Sensor: see Accelerator Pedal Position Sensor

Aqueous Urea: Urea that is mixed with water for delivery as diesel exhaust fluid in the exhaust system of a diesel engine. This triggers a checmical reaction which see the urea become ammonia which will then break apart NOx gasses before they leave the exhaust pipe.

ASE: National Institute for Automotive Service Excellence. An organization that offers a voluntary certification program for automotive technicians. If a technician is ASE certified they have passed an exam administered by ASE to prove some level of competence in automotive service and repair.

Ash: Noncombustible trace minerals and other things found in engine oil that are produced after everything else burns in combustion. Ash deposits can render a catalytic converter ineffective, and will eventually plug a DPF found on modern diesels.

ASTM: see American Society for Testing and Materials

A/T: see Automatic Transmission

ATF: see Automatic Transmission Fluid, do not see Alcohol, Tobacco, and Firearms.

ATF-WS: The newest type of ATF required in Toyota automatic transmissions.

Atkinson Cycle: A four-stroke cycle used in an internal combustion engine that has a shorter compression stroke by way of a delay in the closing of the intake valves. This reduces pumping losses which makes the engine more efficient. The trade-off is a reduction in torque output. This type of engine is used on hybrid vehicles because electric motors easily make up for the reduction in power.

Auto-Ignition Temperature: The temperature at which a fuel or other flammable material will spontaneously combust. Should not be confused with flash point.

Automatic Transmission: A transmission which is capable of automatically selecting the best gear ratio for the operating conditions of the engine.

Automatic Transmission Fluid: A specialized hydraulic fluid used in automatic transmissions that not only lubricates mechanical parts, but also transmits force hydraulically to help the transmission shift gears.

AWD: All-Wheel Drive. A drivetrain configuration that allows all four wheels to help propel the vehicle.

AWG: see American Wire Gauge

Axle Tramp: A condition that affects a live rear axle where the axle twists in place because of applied torque and then springs back before twisting again. This affects many old muscle cars ones the engines get modified to increase output. 2. A great band name.



B+: An abbreviation for battery voltage, or a connection to the positive side of the battery.

B-Pillar: The car roof support at the back of the front doors. Not all cars have a B pillar.

Back Spacing: The distance between the back of the wheel rim and the mounting surface of the rim. Back spacing will determine how the wheel assembly will sit in the wheel arch of the body.

Backfire: Unburned air and fuel being ignited in the intake manifold or in the exhaust. Backfiring out the intake is usually but not exclusively caused by a lean condition, backfiring out the exhaust is usually but not exclusively caused by a rich condition.

Balancer Shaft: A shaft in the engine running parallel to the crank shaft that is weighted in a manner creates vibrations to cancel out vibrations from the crankshaft. This will make the engine operate with a greater degree of smoothness.

Ballast: An electrical transformer used to increase voltage required for some lighting systems to operate. HID headlights require a ballast.

Ball Bearing: An anti-friction device that is part of an assembly with an inner and outer race and hardened steel balls separating them.

Ball Joint: A ball and socket joint typically used in suspension system to allow for flexing between rigid parts. A ball joint allows the suspension to move up and down, and the wheels to turn while steering.

Barchetta: Italian for “small boat.” This term is used particularly by Ferrari to describe any car that is small, open top, with seating for two, and built for racing.

Baro Sensor: A sensor used by various ECUs to monitor barometric pressure. This is especially important for determining air/fuel mixture.

Battery: An electrochemical device used to store direct current for use in electrical and electronic systems.

Battery Council International: A trade organization made up of automotive battery manufacturers. The set standards for battery design.

Battery, Gel Cell: A type of battery that uses a gel electrolyte instead of a regular liquid electrolyte. Usually referred to as an Optima battery which is a brand name. The generic name is a recombination battery. They are heavier-duty than conventional batteries.

BCI: see Battery Council International

BDC: see Bottom Dead Center

Bead: The part of the tire that sits down inside the edge of the rim. This is a very hard and inflexible piece around the inside of the tire that fits into a channel around the edge of the rim.

Before Top Dead Center: A term used along with a specific number of degrees where ignition base timing should be set. 15° BTDC is a common base timing specification.

Bell Housing: The part of a transmission that allows the transmission to bolt to the engine and works as a housing for the torque converter or clutch assembly.

Bell Mouth: A condition affecting a brake drum where the friction surfaces are farther apart across the drum at the opening, versus the back of the drum.

Beltline: The line down the side of a car extending from where the hood meets the base of the windshield. This line a has a major effect on the way a car looks.

Belt, Serpentine: A multi-ribbed belt that wind continuously around all drive and idler pulleys to power vehicle system accessories. Serpentine belts are the type that is found on modern cars as opposed to V belts.

Belt, V: An old style belt that was used to power accessories and vehicle systems. V belts have a cross-section that is V shaped, and they never run more than two different accessories at a time. They also have a higher tendency to squeal when misadjusted.

Bentley: A British auto manufacturer specializing in luxury and performance cars. Based in Crewe, England the company was founded in 1919 by W.O. Bentley. For most of its existence Bentley has been owned by Rolls-Royce, today Bentley is owned by Volkswagen.

Berlinetta: Italian for “little saloon.” A term used by many European auto manufacturers to describe a small sporty two door car. Chevrolet also used the term in association with some Camaro models back in the 70’s and 80’s Berlinetta Camaros had fancier “European” style trim including spoke wheel hubcaps. These type of wheels were known to clash with mullets everywhere so this trim package was dropped in 1985.

Bi-Fuel: A vehicle that can run on two different fuels but not at the same time. An NGV that can run on natural gas or gasoline is called bi-fueled.

Big Block: An engine block, typically a V8, that is built using a larger block than similar engines from the manufacturer that are built using a small block. The difference between these two has nothing to do with displacement, only the overall dimensions of the engine block. Head designs can vary substantially.

Biodiesel: Diesel fuel that is derived from vegetable oils and animal fats. Produced through transesterification of triglycerides found in biological feedstocks using methanol.

Bleeder: A port or opening in a fluid system that allows for the purging of air form the system. Bleeders are used to get all the air out of a hydraulic braking system.

Block, Engine: The main body or housing of the engine. The block contains all the cylinders and the journals for mounting the crankshaft.

Blow-by: Combustion gasses that leak past the piston rings during combustion. Some blow-by is normal, excessive blow-by indicates worn out piston rings, and/or cylinder walls.

Blower: The fan used to move air thought the cabin HVAC system. 2. A slang term for supercharger.

Bluetec: A name used by Mercedes for their clean diesel technology. This term was also used by Dodge on their early clean diesel trucks because Chrysler was owned by Mercedes at the time.

BMW: Bayerische Motor Werken, or Bavarian Motor Works. A German auto and motorcycle manufacturer founded in 1916. They started out building airplanes for WWI but then switched to motorcycles after the war and didn’t build a car until 1928. BMW also owns Mini, and Rolls-Royce.

Body-on-Frame: A chassis design where the body is separate from the frame. All drivetrain, steering, and suspension systems are bolted to the frame and the body is bolted on top of it all.

Bonded Lining: A brake pad or show lining that is glued to the shoe or pad.

Boot: A generic term for any rubber covering that protects mechanical parts. 2. the word used for the car trunk if you drive on the wrong side of the street.

Bottom Dead Center: A term used to describe piston position in the cylinder when it is at the exact bottom of its travel.

Bounce Test: The act of physically bouncing on one end of the vehicle or the other to quickly check the reaction of shocks and struts. If the vehicle continues to bounce when pressure is released the dampeners are bad.

BPP: see Brake Pedal Position sensor

Brake Balance: The level at which each individual brake applies compared to the other brakes. Each brake must apply at the right time and with the right amount of force.

Brake Booster: A device used to provide power assist for application of the brake pedal. Most cars and trucks use a vacuum booster or a hydraulic booster.

Brake Drum: The rotating assembly with the swept friction surface that is acted upon by the brake shoes.

Brake Fade: the point at which the brakes on a vehicle can no longer convert kinetic energy of vehicle movement into heat energy to bring the vehicle to a stop. This is the way that brakes most commonly “go out.”

Brake Fluid: A non-petroleum based hydraulic fluid used to transmit force in the braking system from the driver’s foot the the actuators at each wheel. Brake fluid must be hygroscopic and is thus typically glycol based.

Brake Hardware: The springs and clips and boots associated with brake pad or shoe installation. These parts don’t always need to be replaced when serving brake linings but they must be inspected.

Brake Light: Red lights that illuminate brightly when the brakes are applied t notify other vehicle that the driver intends to slow or stop the vehicle.

Brake Light Switch: A switch attached to the brake pedal that will close when the brakes are applied.

Brake Line: A rubber or metal tube that carries fluid pressure through the brake system hydraulics.

Brake Pads: The serviceable brake lining assembly used on disc brakes.

Brake Pedal Position Sensor: A sensor used to tell the computer the position of the brake pedal. Found in regenerative braking systems and some ABS systems.

Brake Rotor: The rotating assembly with the swept friction surface used on disc brake systems. This is the the part that spins and get squeezed in the caliper by the brake pads.

Brake Shoes: The serviceable brake lining assembly used on drum brakes.

Breaker Bar: A handle for driving sockets that does not contain a ratchet mechanism. Usually used when leverage is needed to break a fastener loose.

Breakout Box: A piece of electronic test equipment that allows access to electrical signals at a connector while keeping the connector hooked up so the system can function normally.

Breather: A passageway or tube or port that allows an expansion or some kind of movement of air.

British Thermal Unit: A measure of energy, typically heat energy. 1 BTU is the amount of energy required to heat 1 pound of water, 1 degree Fahrenheit.

BTDC: see Before Top Dead Center

BTU: see British Thermal Unit

Buick: An American auto manufacturer that specializes in building cars that are a step above the regular working man’s car. Buick is a subsidiary of General Motors that is actually still around. Originally founded in 1899, it is the oldest American auto brand and was the foundation of General Motors.

Bump Steer: A condition that causes the vehicle to steer to the right of the left when traveling over bumps. Usually caused by some defect in the steering or suspension systems.

Bump Stop: A rubber or poly-urethane bumper that keeps suspension components from touching abnormally when the suspension bottoms out. see Strike Out Bumper.



CAC: see Charge Air Cooler

C-Pillar: The roof support on each side of the rear window.

Calibration: A precise adjustment that allows a component to do its job with precision

California Air Resource Board: A California state regulatory agency that is charged with protecting air quality all over the Golden State. Like so many California agencies CARB is a redundant organization similar to the US EPA. To be fair CARB has been around longer than the EPA.

Camber: Wheel alignment angle. The inward or outward tilt of the tire when viewed from the front or rear. inward tilt is negative camber, outward tilt is positive camber. Improper camber will cause irregular tire wear and may cause a pull if cross-camber is too far out.

CAN: see Controller Area Network

Canyonero: A large SUV endorsed by Krusty the Clown. “12 yards long, 2 lanes wide, 65 tons of American pride! Canyonero! Canyonero! Top of the line in utility sports, Unexplained fires are a matter for the courts! Canyonero! Canyonero! She blinds everybody with her super high beams, She’s a squirrel-squashin’, deer-smackin’ drivin’ machine…”

CARB: see California Air Resource Board

Carbon Monoxide: A chemical composed of one carbon atom and one oxygen atom. CO is found in car exhaust and is one of the pollutants that is monitored for determining air quality. CO is a byproduct of combustion and can be harmful to breathe in large concentrations as it displaces oxygen in the blood stream.

Carburetor: A device used for metering fuel into the intake of the engine so as to keep the air/fuel mixture just right for efficient engine operation. It is very imprecise and was made obsolete by the advent of electronic fuel injection. See also gasoline toilet.

Carcus Ply: Layers of rubber extending from bead to bead that make up the underlying body of the tire.

Cardon Joint: A double universal joint found on some driveshafts.

Caster: A wheel alignment angle. The forward or rearward tilt of the steering axis. Negative caster is the forward tilt of the steering axis, positive caster is the rearward tilt of the steering axis. Caster also helps return the wheels to center after a turn. Caster angle does not cause irregular tire wear and will only cause a pull if cross-caster is off too far.

Catalyst: An element used to start a chemical reaction that does not get consumed in the reaction.

Catalytic Converter: An emissions control device found in the exhaust that contains a catalyst to help reduce NOx and oxidize CO and HC’s that result from the combustion process. Often thought to have a negative impact on engine power but this is pure myth.

CDPF: Catalyzed Diesel Particulate Filter see Diesel Particulate Filter

Center Link: The center connecting rod to which the tie rods, idler arm, and pitman arm all attach on a parallelogram steering linkage.

Cetane Rating: A rating for diesel fuel that indicates the ability of the fuel to ignite under heat and pressure. Diesel fuel must have a cetane rating of at least 40. This is essentially the opposite of the octane rating used to describe gasoline’s ability to resist ignition under heat and pressure.

CFPP: see Cold Filter Plugging Point

Charge Air Cooler: A device mounted in front of the radiator that resembles a radiator but is used to cool the intake air after it is compressed by a turbocharger or supercharger. Cooling the intake air charge makes it more dense which will make it more oxygen rich.

Chassis: The structural framework of the car. Any system that attached directly to the chassis or affects chassis function is a chassis system e.g. brakes, suspension.

Chevrolet: An American auto manufacturer founded in 1911 by William C. Durant and Louis Chevrolet. Durant used the company to retake control of General Motors in 1918 after losing control of the company back in 1910. Chevrolet became the volume sales leader for General Motors back in the 1920’s and has held that position ever since.

Choke: A butterfly valve found on top of most carburetors designed to block airflow and enrichen the mixture when the engine is cold. It’s also something you commonly want to do to your car if your daily driver is old enough to be carbureted.

Chrysler: An American auto manufacturer founded in 1925 by Walter Chrysler, and headquartered in Auburn Hills, MI. Chrysler was owned by Mercedes from 1998 until 2007. Chrysler would have gone out of business and had its assets liquidated had it not been purchased by Italian auto maker Fiat in 2010.

CI: Compression Ignition. A method used for igniting fuel in the combustion chamber. Diesel vehicles use this method.

Circuit Breaker: A circuit protection device that contains a bimetallic strip which will deflect when heated during moments of excess current flow. When the breaker cools the device resets itself. These are used in circuits which might be prone to moments of excess current such as power windows and windshield wipers.

CKP: Crankshaft Position Sensor.  A sensor used by various computers to determine the position and rotational speed of the crankshaft.

Cloud Point: The temperature at which paraffin crystals first begin to form in diesel fuel that has been cooled. This is typically around -10° F, and makes running a diesel engine very difficult.

Closed Loop: The programming used by the PCM to control air/fuel ratio once the O2 sensors are warmed up and reading correctly. When the engine is first started it takes anywhere from a few seconds to a few minutes for the PCM to go into closed loop operation. see Open Loop

Clutch: A mechanism that is typically uses interlocking mechanisms to join one rotating assembly to another. 2. The mechanism that engages and disengages a manual transmission from the drive of the engine. 3. The pedal used to operate the clutch on a vehicle equipped with a manual transmission.

CMP: Camshaft Position Sensor. A sensor used by various computers to determine the position and rotational speed of the camshaft.

CNG: Compressed Natural Gas. A form of on-board storage for natural gas as a motor vehicle fuel, typically 3600 psi, with some older systems running 3000 psi. Storing the gas in a compressed state allows the vehicle to have a larger range. When the gas is actually burned in the engine it is not under high pressure.

CO: see Carbon Monoxide

Cold Filter Plugging Point: The temperature at which a diesel fuel filter will get plugged up with paraffin crystals. This is one of the reasons that diesel engines have a hard time running in cold temperatures.

Combustion Chamber: the space between the top of the piston at TDC and the cylinder head where the combustion event takes place.

Combustion Slobber: A condition affecting direct injection diesel engines that is caused by excessive idle time. When the engine idles, temperatures drop so much that water and fuel condense in the exhaust stream and leave a sticky abrasive residue in the exhaust system. This is why idling a diesel is not good. Also known as Wet Stacking, or Turbo Slobber.

Common Rail Injection: A type of diesel fuel injection system where a high pressure fuel pump adjusts fuel pressure in a fuel rail that is common to all injectors. Each injector can be controlled independently by the PCM to control the way the engine functions.

Composite: A material or even a specific part that is made up of multiple materials.

Compression Ratio: The difference between the volume of the cylinder and combustion chamber with the piston at TDC and BDC. The higher the compression ratio, the more power an engine can produce up to a point.

Compression Test: A method of testing engine cylinder integrity by installing a pressure gauge into the spark plug hole and cranking the engine to see how much pressure will build in the cylinder. Normal compression can be anywhere between 100 to 200 psi on a gasoline engine.

Compression Test, Wet: A compression test that is performed with a few drops of oil squirted into the cylinder. This is done after a standard compression test. If the wet compression test numbers are higher than the standard test, it means the piston rings are worn because the oil will help to hold compression.

Control Arm: A suspension link that attached to a pivot at the vehicle frame or chassis, and to the top or bottom of the knuckle with a ball joint. This is one of the main support members for many independent suspension systems

Controller Area Network: A standardized communication protocol used on all in car networks since the 2008 model year.

Coolant: The fluid used in the engine cooling system. This formulation is ideally made from equal parts water and ethylene glycol. Engine coolant must resist boiling when the engine is very hot but it must also resist freezing when parked outside in the winter.

Coupe: A two door car with a closed roof an a rear deck/trunk.

Cowl: The area at the base of the windshield. This area usually contains the air inlets where air is drwan into the vehicle by the HVAC system.

Cowl Shake: A negative side effect of a chassis that is not very stiff. The center section of the car shakes and vibrates from the area of the firewall between the passenger area and the engine compartment. Sometime more pronounced on convertibles but can be experienced on other kinds of cars.

CP: see Cloud Point

CR: see Common Rail Injection

Crankshaft: The primary rotating assembly within the engine

Cross-Caster: Wheel alignment angle. The difference in degrees between the left-side caster angle and the right-side caster angle.

Cross-Camber: Wheel alignment angle. The difference in degrees between the left-side camber angle and the right-side camber angle.

Cross-Steer Steering Linkage: A very simple a flexible linkage that uses a drag link attached to the pitman arm and the steering knuckle on one side of the vehicle. The opposite wheel is attached through a single tie rod that goes between both knuckles. This linkage is usually found on 4WD vehicles with a solid front axle.

Cup Seal: A seal in hydraulic braking systems that hold brake fluid pressure in the system as force is exerted on mechanical pistons. The higher the pressure against the cup seal the tighter it holds the pressure. Typically found in master cylinders and wheel cylinders.

Curb Weight: The weight of the vehicle when it is empty. This is not the same as the GVWR listed on the information label in the driver’s door jamb.

CV Joint: Constant Velocity Joint. A joint in a drive shaft that allows the shaft to bend in any direction while still rotating. Typically found in the front axle of front-wheel drive cars.

CVCC: Compound Vortex Controlled Combustion. A term used by Honda to describe the combustion process used in some of their engines back in the 70’s and 80’s The engines used a prechamber in the combustion chamber with a small third barrel in the carburetor. This small air/fuel charge was used to ignite the main charge.

Cylinder: The part of the engine block where the piston moves up and down as the engine produces power. The more cylinders an engine has the smoother and more responsive the performance. The number of cylinders is only tied to engine output when considered along with total cylinder displacement.



Dash Board: The panel in front of the driver and passenger where all the instruments and controls are mounted. This name comes from the old carriages which had a dash board in front of the driver to dash away dirt and debris kicked up by the horses.

Data Link Connector: The diagnostic connector where a scan tool can be attached in order to interface with an ECU. On OBD I vehicle the DLC can be any shape or size and located anywhere on the vehicle. Under OBD II these things were standardized across all makes and models.

Data Bus: The wires that carry shared network data from one ECU to another. Data buses usually consist of the twisted pair of wires.

Datastream: The stream of serial data available from an ECU on on-vehicle network that pertains to the electronic functions of the vehicle. This data can give a technician clues to help them diagnose a problem.

Datsun: In modern parlance, a vehicle brand manufactured by Nissan intended for sale in emerging markets only. see Nissan

DC-to-DC Converter: the components found in hybrid and electric vehicles that takes voltage from the HV battery and steps it down to about 14 volts to charge the auxiliary battery and to run vehicle accessories.

DC Motor: An electric motor that use DC current to operate. A starter motor is a DC motor.

DDI: see Diesel Direct Injection

Dead Cat Hole: The space between the tire and the fender around the wheel well. Trucks and four-wheel drive vehicles have larger dead cat holes than sedans.

Dead Pedal: A footrest for the driver on the floor to the left of the pedals. Sometimes it might have a resemblance to a pedal.

Deceleration Fuel Cutoff: A mode of operation by the PCM where it will shut down injector during deceleration to save fuel.

Deck: The area on top of the trunk lid. 2. The top of the engine block where the cylinder head is mounted.

Deep Cycling: Running a battery nearly dead before recharging. Most car batteries do not tolerate deep cycling and will have a shortened life when exposed to such use.

DEF: Diesel Exhaust Fluid. Fluid that is used on modern clean diesel after treatment systems to reduce NOx emissions. see Urea

DFCO: see Deceleration Fuel Cutoff

Dependability: Something that completely escapes the British auto manufacturers.

Detonation: A combustion problem where fuel explodes violently in the cylinder, usually prematurely.

Dex-Cool: A proprietary long-life engine coolant used by GM. This was the first of the extended-life coolant formulations found on the market, and it is usually orange in color instead of the traditional green. Many people think that if you put normal green coolant in a GM vehicle that requires Dex-Cool you will ruin the cooling system. this is completely false.

Dielectric: Something nonconductive used in an electrical circuit. The plate between the two conductors in a capacitor is a dielectric.

Dielectric Grease: A nonconductive lube used in electrical connections to block oxygen from corroding connectors and terminals. This can be used on battery cable ends to prevent corrosion of terminals.

Diesel Direct Injection: A diesel injection system that injects fuel directly into the cylinder as opposed to the indirect injection systems used by some diesel engines. Direct injection systems are the current standard in diesel injection setups.

Diesel Engine: An internal combustion engine that uses high pressure and concentration of heat to ignite the fuel in the combustion chamber.

Diesel Fuel: A hydrocarbon mixture made up of longer hydrocarbon chains used as fuel for diesel engines. Diesel fuel is more like motor oil in consistency and volatility than gasoline.

Diesel Oxidation Catalyst: A diesel exhaust after-treatment system responsible for oxidizing hydrocarbons and carbon monoxide found in diesel exhaust emissions. This is similar the catalytic convert used on gasoline powered vehicles. The DOC is the first step in the after-treatment system.

Diesel Particulate Filter: An emissions control device found on diesel-powered vehicles built from 2007 onward. This device is meant to capture soot particles from the exhaust and store them until they can be burned where they are trapped to prevent them from ever making it out into the air intact.

Diesel, Rudolph. A German engineer who invented the diesel engine in 1897.

Dieseling: Also known as engine run-on, a condition where an engine will continue to run after the ignition is switched off. This usually occurs when fuel is available and cylinders are hot enough to ignite the fuel uncontrollably without a spark.

Differential: A gear set-up in the drivetrain at the axles that allows torque transmission to both drive wheels while also allowing them to rotate at different speeds when the vehicle turns.

Digital: An electronic signal that is either on or off, high or low, with no variation in between.

Digital Multimeter: A digital tool for testing electrical systems that is capable of reading volts, amps, and ohms, as well as other things.

Distributor: A component in old style ignition system that contains a rotor driven by a shift from the engine. The rotor transfers the ignition spark to the appropriate spark plug wire as it spins around under the distributor cap.

DLC: see Data Link Connector

DMM: see Digital Multimeter

DOC: Diesel Oxidation Catalyst

Dog Leg Manual: A manual transmission that engages first gear by pulling the stick to the left and down, instead of up. This is considered better for racing because it makes for a faster 2, 3 shift.

Dog Tracking: A condition experienced by a car with an excessive thrust angle that causes the  rear wheels to travel in a line that is not inline with the front wheels. Almost as if the rear axle is sideset from the front axle.

Dodge: 1. An American auto manufacturer founded in 1915 by Horace and John Dodge. Prior to building their own cars the Dodge Brothers built engines for other car makers of the day. Dodge was purchased by Chrysler in 1928, they have been together ever since. 2. To avoid.

DOHC: Duel Overhead Cam. A valve train design that uses two camshafts per cylinder head. One camshaft to operate the intake valves, one camshaft to operate the exhaust valves. This is the valve train configuration that allows for the greatest volumetric efficiency because it can operate the most and the biggest intake and exhaust valves.

DPF: see Diesel Particulate Filter

Drag Link: The link that connects the pitman arm the the knuckle or tie rod on a cross-steer steering linkage. Sometimes the center link of a parallelogram steering linkage is referred to as the drag link.

Drive-by-Wire: Another name for electronic throttle control systems that do not use an old style throttle cable.

Driveshaft: A shaft used to send power from the transmission or transfer case to a differential in the center of an axle. Usually used to describe such shafts on RWD and 4WD vehicles.

Droptop: Another name for a convertible.

Dry Sump: A lubrication system where the oil that in normally stored in the oil pan or sump below the crankshaft is actually stored on a separate tank off to the side of the engine. This allows the engine to sit lower in the car to lower the center of gravity of the entire vehicle. see Wet Sump

DTC: Diagnostic Trouble Code. A numeric or alphanumeric sequence stored in the memory of an ECU when a fault is detected within the system the ECU controls. This must usually be extracted using a scan tool.

Dual-Fuel: A vehicle that runs on two fuels at the same time. This term is most commonly used to describe a vehicle that runs on diesel fuel and natural gas at the same time. A tiny bit of diesel fuel is used to ignite a larger charge of natural gas in the engine cylinders.

Dual Ignition: An ignition system that uses two spark plugs per cylinder located on opposite sides of the combustion chamber from each other. This is done specifically to help the engine meet federal emissions standards. The modern Chrysler HEMI engines have such a system for this purpose. It is not intended to help produce more power.

Dust Shield: A metal plate or rubber boot used to cover a component to protect it from the elements and other intrusions.

Duty Cycle: An electrical control function used to characterize the cycle of an electrical device turning on and off. Duty Cycle is on-time expressed as a percentage of total cycle time.

Dwell: The on-time of the primary ignition coil winding expressed in degrees of crankshaft rotation.

Dynamometer: A piece of test equipment used to test the output of a mechanical device



E10: A term used to describe gasoline that is made up of 10% ethanol for the purpose of oxygenation of the fuel. The ethanol molecule contains an oxygen atom which helps clean up the combustion process and raise the octane rating of the fuel.

E85: A motor fuel made up of 85% ethanol and 15% gasoline. This fuel can be used in any vehicle labeled “FlexFuel.”

EBCM: see Electronic Brake Control Module

ECM: Electronic Control Module. This is a generic term applied to any computerized control unit. Also see ECU

ECM: Engine Control Module. The computer responsible for controlling the functions of the engine. Also see PCM

ECT: Engine Coolant Temperature. Also used to describe the sensor that measure coolant temperature.

ECU: Electronic Control Unit. This is a generic term applied to any computerized control unit. Also see ECM

EFI: see Electronic Fuel Injection

EGR: Exhaust Gas Recirculation. An emissions control system used to reduce the formation of oxides of nitrogen by recirculating inert exhaust gasses back through the intake to displace oxygen in the combustion chamber.

EGT: see Exhaust Gas Temperature

EGT Sensor: A sensor for monitoring exhaust gas temperatures, typically used on diesel engines to monitor the after treatment systems, or in performance applications to make sure pistons and valves are not getting too hot.

Electro-Motive Force: The force behind the flow of electrons that results from the amount of potential difference between the positive and negative sides of the circuit. The same thing as voltage but it sounds cooler.

EMF: see Electro-Motive Force

Elastomer: A word used to describe rubber when you want to sound really smart.

Electric Fuel Pump: A fuel pump that is motivated by an electric motor. This is the standard on all vehicles with electronic fuel injection. The electric fuel pump is usually mounted in the fuel tank.

Electric Motor: A device that uses electromagnetism to produce torque.

Electricity: The free movement of electrons from one atom to another. These electrons can be made to perform work as they follow a specific pathway.

Electrolysis: A method of using electricity to drive a chemical reaction usually used to separate elements in a compound.

Electrolyte: The mixture of water and sulfuric acid found in a battery. This allows a release of electrons from the battery. When a battery is charged the concentration of acid goes up.

Electromagnet: A magnet made by wrapping an iron core with a thin wire strand and then applying electricity to the strand of wire. Most magnets used in the function of the automobile are electromagnets.

Electromagnetic Interference: Electrical noise that is produced when wires carrying strong electrical signals induce current into other wires that run nearby.

Electromagnetism: Principles that deal with the relationship between electricity and magnetism. One can always be used to produce the other.

Electron: A negatively charged particle found in an atom that can be released from or drawn to an atom freely. This is the basis of electricity.

Electronic Brake Control Module: A term used by GM to describe the ABS control unit.

Electronic Fuel Injection: A fuel injection system that is electronically controlled. Electronic controls make fro greater accuracy in fuel control and the ability to have on-board diagnostics.

Electronic Ignition: A system that uses a heavy-duty transistor to switch the ground side of the primary coil winding off and on to create a spark in the secondary winding of the coil. This was common on all vehicle models by the mid 70’s and represented a major step forward in making cars more reliable.

Electronic Power Steering: A way of providing power assist for steering that uses an electronically controlled assist motor instead of the older style hydraulic systems.

Electronic Spark Advance: An ignition system that will advance spark timing with computer controls and sensors.

Electronic Variable Orifice Power Steering: A hydraulic power steering system that uses an electronically controlled variable orifice to determine how much assist is provided.

Emergency Brake:  A misnomer usually used in reference to the park brake, no cars or trucks are equipped with emergency brakes.

EMI: see Electromagnetic Interference

Enable Criteria: Certain operating parameters that must be met for a system monitor to run under OBDII regulations.

End Play: The amount of freeplay or movement in-line with an assembly of parts.

Engine Analyzer: A computerized piece of equipment that can be attached to the ignition system and other systems of the engine to check their performance. This kind of machine is obsolete by modern standards because it is not longer practical to have a machine of this nature that can generically hook up to any car.

EPS: see Electronic Power Steering

ESC: Electronic Stability Control, see Anti-Skid Control

ESP: Electronic Stability Program, see Anti-Skid Control

Ether: see Ethyl Ether

Ethanol: Ethyl Alcohol. Chemical formula, C2H6O. Used as a fuel for the internal combustion engine, or as an oxygenating additive for regular gasoline. Most ethanol used in the U.S. comes from corn. 2. Used as the active ingredient in adult beverages to make you forget your troubles. It’s also a form of liquid courage.

Ethylene Glycol: The base chemical used in most types of engine coolant and antifreeze.

Ethyl Ether: Common starting fluid. A fluid sprayed form a aerosol can into the intake of an internal combustion engine to help it start. Primarily used on diesel engines because it has a very low autoignition temperature and can put enough heat into the combustion chamber of a diesel engine to help it start even when the engine or fuel system is compromised by some kind of failure.

EV: Electric Vehicle. A vehicle that runs on electricity from a battery powering an electric motor. No internal combustion engine is present.

EVO: see Electronic Variable Orifice Power Steering

EVAP: see Evaporative Emissions Control System

Evaporative Emissions: hydrocarbon emissions from a vehicle that come from the evaporation of raw fuel that can escape from the fuel system. These emissions most commonly escape when refueling a vehicle.

Evaporative Emissions Control System: An emissions control system used to contain raw fuel vapors that can escape from different areas of the fuel system. These vapors are diverted from above the fuel in the gas tank into a canister where they are contained in activated charcoal until being released into the intake manifold during engine operation, where they are drawn into the cylinders and burned.

Exhaust Gas Temperature: The temperature of the exhaust as it leaves the engine. Important to monitor as an indication of combustion temperatures. High-performance diesels need to watch this very closely.

Exhaust Manifold: The pipe or tube assembly attached to the cylinder head that channels exhaust from the exhaust ports to the exhaust pipe.

Exhaust Stroke: The last stroke in the Otto Cycle wherein exhaust gasses are expelled from the cylinder by the upward movement of the piston with the exhaust valve(s) open.

Exhaust Valve: The valve located in the cylinder head that opens to let the piston push exhaust gasses out during the exhaust stroke. Most engines have 1 or 2 exhaust valves per cylinder.

Expansion Valve: A metering valve used in and air conditioning system to regulate the flow of refrigerant into the evaporator core. This marks the end of the high pressure side and the beginning of the low pressure side.



FAME: see Fatty Acid Methyl Ester

Fatty Acid Methyl Ester: The basis of biodiesel that results from the process of transesterification of fats such as vegetable oil.

FCA: Fiat Chrysler Automobiles. A large multinational auto manufacturer based in Turin, Italy. Chrysler has been purchased by Fiat since Chyrsler went through bankruptcy starting in 2009. Brands that currently fall under the FCA umbrella include: Fiat, Chrysler, Alfa Romeo, Dodge, Lancia, Ram, Jeep, Maserati, and Ferrari.

Ferrari: An Italian auto manufacturer that specializes in building exotic super cars. Founded in 1929 as an auto racing company they didn’t start building cars themselves until 1947. Scuderia Ferrari is the racing company that is still a world leader in motorsport.

FFV: see Flex-Fuel Vehicle

FIA: Federation Internationale De L’Automobile. An international motorsport governing body located in Paris, France. These are the guys in charge of Formula 1.

Field Winding: An insulated conductor wound around a pole piece to form an electromagnet. Found in a stationary position in starter motors in order to oppose the magnetic field created in the armature windings.

Firing Order: The order in which cylinders of the engine fire. This is usually determines by crankshaft design and cylinder ordering.

Flash Point: The temperature at which a fuel will produce ignitable vapors. Gasoline -45° F, Diesel 126° F. This is not the point at which spontaneous combustion occurs.

Flash Programming: The programming that must be performed when an ECU is replaced, or the programming requires an update.

Flat Rate: A term used in auto repair estimating whereby the cost of a repair is determined by the hours required to make the repair multiplied by the hourly shop labor rate.

Flex-Fuel Vehicle: A vehicle with a fuel system that is capable of using E85, gasoline, or a combination of the two.

Float Bowl: A small fuel containment area found inside a carburetor where fuel level must be maintained within a specific range in order to maintain proper engine function.

Float, Carburetor: The float in the float bowl that attaches to the needle and seat. As the float drops the needle and seat opens to let more fuel into the float bowl.

Ford: Ford Motor Company. An American auto manufacturer founded by Henry Ford in 1903.

Formula 1: The highest class of racing administered by FIA. Formula 1 refers to the rules and requirements for this class of racing. The cars are single seat open wheel race cars using the latest technology and racing on tracks of all shapes and sizes. Formula one is considered the fastest and most advanced racing to take place on road-like courses.

Fossil Fuel: Any organic fuel that is formed in the Earth’s crust such as petroleum or natural gas.

Four-Wheel Steering: A vehicle steering system that turns the back wheels in addition to the front wheels to steer the vehicle. At slow speeds wheels turn in the opposite direction. At high speeds the wheels turn in the same direction.

Frequency: In electrical terms, defined as cycles per second.

Front Main Seal: The oil seal at the front of the engine that seals the end of the crankshaft. On some engines it actually seals pressurized oil in the front main bearing assembly, on other engines it just seals oil in the front cover.

Front-Wheel Drive: A drivetrain configuration whereby the vehicle is driven using the front wheels. FWD vehicles usually have the engine mounted in a transverse manner. They are better on snow and ice than RWD cars because as the car is being steered, the wheel pull in the direction the driver wants to go.

FRP: see Fuel Rail Pressure

FTP: see Fuel Tank Pressure Sensor

Fuel Injector: A fuel control mechanism used to spray pressurized fuel into an intake manifold or engine cylinder. All modern fuel injectors are electronically controlled.

Fuel Pressure: The pressure in the fuel system produced by the fuel pump. This pressure must be correct in order to maintain good driveability.

Fuel Pressure Regulator: A device that controls the amount of pressure in the fuel system. Typically mechanical in nature and located at the outlet of the fuel rail, or with the fuel pump in the tank.

Fuel Pump: An electrical or mechanical device responsible for moving fuel from the tank, to the metering mechanisms at the intake manifold.

Fuel Pump Relay: The electronic relay that controls the flow of current to the fuel pump. This relay is controlled by the PCM.

Fuel Rail: The pipe of tube that acts as an accumulator of fuel pressure to be distributed to fuel injectors in all multiport or direct injection electronic fuel injection systems.

Fuel Rail Pressure: Fuel pressure in the fuel rail of a common rail diesel injection system. This is a critical part of insuring proper fuel system function.

Fuel System: the fuel distribution system that stores fuel and brings it to the engine. Tank, lines, pump, etc.

Fuel System Monitor: The OBDII monitor that tracks short term and long term fuel trim for excessive correction. This monitor makes sure that the engine is not running too rich or too lean.

Fuel Tank: The fuel storage vessel found on any car or truck. If you want to be fancy about it you can call it a fuel cell.

Fuel Tank Pressure Sensor: A pressure sensor responsible for monitoring fuel vapor pressure in the tank. this is used to monitor for leaks in the evaporative emissions system.

Fumigation: The process of flooding an intake manifold with a gaseous fuel.

Fuse: A circuit protection device installed in series with a circuit. If the circuit is allowed to draw too much current because of a short to ground the fuse will melt internally and open the circuit so o current can flow.

Fusible Link: A circuit protection device similar to a fuse except the fusible material usually appears the same as an ordinary wire, and is not mounted in a fuse block. Fusible links are not used much anymore in modern cars and trucks.

FWD: see Front-Wheel Drive



G Force: The amount of force applied to an object by gravity.

G Lader Supercharger: A type of supercharger that uses a rotating eccentric within the compressor housing to create boost. This type of supercharger tends to be quieter than others.

Gallery: A passage or conduit thorough a casting. In an engine block the oil passageways are referred to as oil galleries.

Galvanic Corrosion: A reaction where one metal breaks down in the presence of another dissimilar metal, when both are involved in a transfer of electrons or electrical flow, in the presence of a chemical electrolyte. When this process occurs at a place where it is not wanted we call it corrosion. When it happens where intended we call it a battery.

Galvanize: The chemical process of coating ferrous metals with a zinc coating to prevent corrosion.

Gas To Liquid: The process of refining natural gas into liquid fuel.

Gasket: A flat seal installed between stationary parts to seal fluids in and other things out. Usually made from paper, rubber, cork, or steel.

Gasoline: A refined hydrocarbon of high flammability, and high volatility that is the most common type of automotive fuel.

Gasoline Direct Injection: A fuel injection system where gasoline is injected at very high pressure directly into the combustion chamber. These systems tend to increase thermal efficiency of the engine.

Gassing: The formation of hydrogen and oxygen during charging of a lead acid battery. These gasses will escape through vents when pressure in the case gets too high. It’s chemistry, not potty humor.

GDI: see Gasoline Direct Injection

Gear: A toothed wheel used in mesh with other such gears to transmit typically rotational force. 2. An abbreviation for gear ratio used to describe a selected gear ratio in the transmission.

Gear Pump: A pump that contains two gears in mesh that move fluid through a system. Commonly used as oil pumps for lubricating engines.

Gear Ratio: The number of turns of an input shaft compared to the number of turns from the output shaft. Used in relation to transmissions and drive axles or differentials.

Gear Reduction: A gear ratio that results in a reduction of speed with a multiplication of torque. Small gear driving a larger gear.

General Motors: An American auto manufacturer founded in 1908 by William C. Durant. Some of the brands that fall under the GM umbrella presently, or in the past are: Chevrolet, Buick, Cadillac, Hummer, GMC, Oldsmobile, Opel, Holden, Vauxhall, Pontiac, Saturn.

Gel Cell Battery: A battery that uses a gel based electrolyte between the plates. Quite often the plates in this kind of battery are spiral in shape. Sometimes they are referred to as Optima batteries bu this is just a brand name.

Gelling: The crystallization of wax molecules in diesel fuel that occurs at low temperatures.

GHG: see Greenhouse Gas

Glass Pack: A type of old muffler design where the exhaust gasses pass straight through the center of the device. Around this center tube are holes drilled opening into a chamber that is filled with fiberglass. This provides some sound dampening but not very much. That’s the whole idea, in addition to less restriction for exiting exhaust gasses. The term glass pack is antiquated because anytime a car with a loud exhaust drives by he mentions something about glass packs.

Glitch: A brief electrical or electronic abnormality. this will usually cause erratic operation of an electronic system.

Glow Plug: A small heating element found in the cylinders of some diesel engines. This heater provides the initial heat necessary to ignite the fuel for the first time at start-up.

GM: see General Motors

Grand Tourer: A sports car that is made for driving long distances. Sometime the term Gran Turismo is used this is the same thing but in Italian.

Gran Turismo Omolagato: An Italian term used to describe a model that has been improved or modified for the track while still being street legal. Many auto manufacturers use this term, not just Ferrari, although the Pontiac GTO is named after the Ferrari.

Gray Cast Iron: An common material used to cast engine parts, mostly engine blocks. It has many good properties but like any cast iron it is very heavy so manufacturers have been moving away from it for many years.

Greenhouse: The glass or windows surrounding the passenger area.

Greenhouse Gas: Any gas that tends to increase heat retention in the air. e.g. every breath you exhale, bovine flatulence.

Gross Vehicle Weight Rating: The maximum legal weight of the vehicle when fully loaded. This is found on the door label on most vehicles and is not the same as the curb weight.

Ground: The most negative point in an electrical circuit. The side of the circuit after the load. No voltage should exist on the ground side of a circuit. In the automobile the negative battery cable and the ground off all electrical circuits attached to the frame or chassis of the vehicle.

GT: see Grand Tourer

GTL: see Gas To Liquid

GTO: see Gran Turismo Omolagato

GVWR: see Gross Vehicle Weight Rating



Half Shaft: The drive axle used on a front-wheel drive vehicle between the engine and transmission, or any drive shaft on a rear-wheel drive vehicle used between a stationary differential and wheel hub assembly. Sometimes called a CV axle.

Hardtop: A convertible with a removable top that is not made from cloth. Sometimes the top folds into the area in front of the trunk and sometimes it must be stored elsewhere when removed.

Harmonic Vibration: The wavelike movement of vibrations along a shaft. Vibrations through a crankshaft. 

HC: see Hydrocarbon

HCCI: see Homogeneous Charge Compression Ignition

Helmholtz Resonance: A phenomenon that occurs inside intake manifolds used to increase volumetric efficiency. This resonant frequency is related to the back and forth movements of pressure waves of air in the manifold. Tuned ports use this frequency to get more air into the combustion chamber on the intake stroke.

Heptane: The seventh hydrocarbon chain. Used in the formulation of gasoline.

Head, Cylinder: The part of the engine that bolts above the cylinders, contains intake and exhaust valves, and holds compression in the cylinder.

Head Gasket: The gasket that seals the cylinder head to the engine block deck. This is typically the biggest gasket in the engine and the most important as it must seal coolant passages, oil passages, and engine combustion chambers from each other and from the outside world.

Heat Checking: Small shallow surface cracks found on the friction surface of a brake rotor or drum caused by getting the breaks too hot.

Heated Oxygen Sensor: An O2 sensor that contains a heater circuit. The heater allows the oxygen sensor to begin functioning more quickly after engine start so the fuel system can get into closed loop operation sooner.

Heater Core: a small radiator like device usually located under the dash that allows the passenger heating system to remove heat from the engine cooling system in order to heat the passenger area.

Hemi: A term primarily used by Chrysler to describe its line of V8 engines which used a hemispherical or pent-roof combustion chamber design. This term is applied as if a hemi engine is unique to them but most engines have been using that design for decades now. In fairness, Chrysler pioneered this kind of efficient combustion chamber design back in the late 50’s. Why they ever quit building them back in the old days is a mystery.

Hemispherical Combustion Chamber: A very efficient combustion chamber design using overhead valves which are placed at angles allowing the intake valve(s) to face towards the exhaust valve(s). This allows for better flow through the chamber. This design has been modified over the years into what is now called a pent-roof hemi. This keeps the efficiency of the hemis but also allows for cleaner emissions.

Hertz: A unit of measurement that counting the number of times an electronic cycle repeats itself. 1 hertz is one cycle per second. 1 kilohertz is 1000 cycles per second. 1 megahertz is 1,000,000 cycles per second.

HEUI: see Hydraulically activated Electronic Unit Injector

HEV: Hybrid Electric Vehicle. Any car that uses a gasoline engine and an electric motor to provide power for the wheels.

HID: see High Intensity Discharge Headlights

High Intensity Discharge Headlights: Headlights that use a special bulb that produces light using an electric arc to produce light instead of using a filament like regular bulbs. A ballast is used to step the voltage up to the required level. HID headlights are brighter than standard halogen lights and appear blue, especially from a distance.

High Occupancy Vehicle: A designation given to vehicles that contain more than one occupant, thus qualifying them to travel in the HOV lane on the freeway.

High Side Driver: A driver within an ECU that controls an output by connecting the circuit to voltage.

Homogeneous-Charge Compression Ignition: A combustion process that allows a very lean mixture of gasoline to ignite without the use of a spark plug or ignition system. this further increases thermal efficiency over the normal GDI systems that are common today. Currently in the experimental stage.

Homologation: The approval process for a race car. In some racing leagues, the cars that are used must also have a street legal variant that must sell in high enough numbers to meet racing criteria. These cars often amount to just a street legal race car. This makes them rare, fast, and very desirable. The term GTO is used by some manufacturers to denote their homologation models.

Honda: A Japanese auto and motorcycle manufacturer founded in 1946 by Soichiro Honda. Honda builds more internal combustion engines than any other company in the world as well as building more motorcycles than anyone else.

Horse Power: A measure of the rate at which force is applied. 1 HP equals the power needed to raise 550 lbs. 1 vertical foot. First defined by James Watt.

HOV: see High Occupancy Vehicle

HP: Horse Power.

Hub Cap: A cover that attaches to the wheel and usually covers the lug nuts and hub. Usually meant to be decorative.

Hub, Wheel: The foundation of the wheel assembly usually pressed into the center of the wheel bearing assembly. The hub contains the mounting flange for the tire assembly and the lug studs to which the tire and rim attach.

HVAC: Heating Ventilation and Air Conditioning, the system of the vehicle responsible for passenger comfort

Hybrid: A vehicle that uses two power sources such as gasoline and electricity.

Hybrid, Micro: A parallel hybrid drivetrain that uses a motor generator primarily for the purposes of idle stop and regenerative breaking. This system provides the smallest amount of fuel economy increases but is also generally much cheaper than more complex hybrid systems. Many vehicle equipped with such systems are not even referred to as being hybrid.

Hybrid, Parallel: A hybrid vehicle where the two power sources are arranged to work at the same time to assist each other in applying torque to the wheels. Many of these types of hybrids are also referred to as mild hybrids because the electric motor is not very capable without the assist of the gasoline engine. Most Honda hybrids are parallel.

Hybrid, Series: A hybrid drivetrain where the gasoline engine works to provide power for the electric motor. The gasoline engine has no mechanical connection to the wheels, it only serves to drive a generator. Diesel electric locomotives are series hybrids.

Hybrid, Series Parallel: A hybrid drivetrain that is capable of acting like a parallel system or a series system. This type of set up is usually characterized by an electric drive motor that is capable of driving the wheels alone, or with the help of a gasoline engine. Toyota hybrids use this configuration.

Hydraulic: The action of using pressurized liquid in an enclosed system to transmit force. Hydraulics can also be used to multiply force as it is transmitted.

Hydraulically activated Electronic Unit Injector: A fuel injection system used on some diesel engines that uses high-pressure engine oil controlled by an electronic solenoid to build even higher-pressure in the fuel and inject it. Similar to the old mechanical UI systems but with much more variability. The 7.3 and the 6.0 Powerstroke engine use this system.

Hydrocarbon: 1. A molecule made up of hydrogen and carbon that can take various shapes based on the way the atoms are arranged. Gasoline is a hydrocarbon that is straight, refereed to as a chain. Benzene is a hydrocarbon in the shape of a ring. 2. A harmful chemical component of car exhaust that reacts with sunlight to form photochemical smog. The HC’s in-car exhaust are essentially unburned gasoline.

Hygroscopic: A term used to describe something that repels water.

Hyundai: A Korean auto manufacturer founded in 1967. Hyundai didn’t start selling cars in the U.S. until 1986. They are currently the 4th largest auto manufacturer in the world.



I-4: An abbreviation for an inline 4 cylinder engine, a very common configuration today.

I-5: An abbreviation for an inline 5 cylinder engine, not a very common configuration but it is found on some engines today.

I-6: An abbreviation for an inline 6 cylinder engine, This has been a fairly common configuration over the years.

I-8: An abbreviation for an inline 8 cylinder engine, This was somewhat common long ago but has not been used in many decades because ti is difficult to package under the hood and it’s so long the torque of the engine in operation tends to slowly pull it apart at the seams.

IAC: Idle Air Control. The system that controls idle speed on computer controlled engines using and IAC solenoid or valve to regulate airflow past the throttle plate.

IAT: see Intake Air Temperature

IAT Sensor: The sensor used to determine the density of the intake air charge. Air density is tied to temperature and oxygen density which will affect air/fuel ratios.

ICE: Internal Combustion Engine. This abbreviation is usually used to describe the engine used in hybrid electric drivetrains.

I.D.: Inside Diameter. A measurement of a tube or pipe.

IDI: see Indirect Injection

Idle Stop: the function of a hybrid vehicle that allows the ICE to shutdown when the vehicle is at idle to save fuel.

Idler Arm: The piece of steering linkage found in a parallelogram steering set up that supports the center link on the opposite side of the vehicle from the pitman arm.

IDK: I don’t know. A bit of texting jargon used by the kids.

IDM: see Injector Driver Module

iForce: A nonsensical term used to describe engines used in the Toyota Tundra. Apparently the Tacoma engine don’t get cool names, and in case you were wondering, this engine is not related to the iPhone and is not manufactured by Apple. see also Triton, Magnum, Vortec

IGBT: see Insulated Gate Bipolar Transistor

Ignition: The point at which the air/fuel mixture begins to burn

Ignition Control Module: The electronic device that contains the transistors that control current flow through the primary ignition coil wingdings. This module is controlled by the PCM.

Ignition Delay: The delay between injection of diesel fuel into the combustion chamber and the point a which the fuel actually ignites. Controlling ignition delay leads to much more efficient operation of a diesel engine.

Ignition System: The system found on gasoline engines that is responsible for the spark production, and spark distribution necessary to burn the air/fuel mixture.

Ignition Timing: The timing between the spark arriving at the spark plug electrodes and the position of the piston in the cylinder. Proper ignition timing is critical for good driveability.

IHC: International Harvester Company. An American manufacturer of farming equipment, heavy-duty trucks, and 4WD SUVs. Founded in 1902, the company now goes by the name Navistar International.

I/M: Inspection Maintenance. Another name for an emissions test.

I/M 240: An emissions test where the vehicle is driven on a dynamometer for 240 seconds under various load conditions and at various speeds.

IMA: see Integrated Motor Assist

Impellar: The rotational piece in a water pump that creates positive pressure.

In-Car Temperature Sensor: A thermistor located in the passenger area to measure the temperature as an input for the climate control system.

Included Angle: A front axle alignment angle. SAI plus camber on the same wheel, when camber is negative.

Indirect Injection: An engine design usually used on diesel engines that has a prechamber where fuel is injected and ignited before moving out into the regular combustion chamber.

Induction Motor: A motor in which induction is used to create a magnetic field in the rotor without the need for brushes or a commutator. Often used in electric vehicles.

Inertia: A natural resistance found in an object that makes a change of direction or motion difficult.

Inertia Switch: An electrical switch typically used in the fuel pump circuit that will open if there is a sudden change in dynamic inertia, I.E. the car smacks into a wall. This shuts off power to the fuel pump to prevent fuel from leaking.

Infiniti: A Japanese luxury car brand owned by Nissan, founded for the North American market in 1989.

Injector Driver Module: The ECU separate form the PCM that is responsible for handling the power to the injectors and controlling the ground side. This unit is found on diesel engines in particular because the injectors they use handle a high amount of voltage and current.

In-line Injection Pump: An injection pump that uses a separate piston and cylinder to inject fuel into each cylinder. Each injection piston is driven by the camshaft. Electronically controlled system integrate an electronic solenoid to precisely control injection.

Input Speed Sensor: A speed sensor used to measure the speed of an automatic transmission input shaft rotation. This is needed in order to help the transmission shift properly.

Instrument Panel: The panel in the dash in front of the driver where all the gauges are located.

Insulated Gate Bipolar Transistors: A type of heavy-duty transistor used to control current flow to the motor/generators in a hybrid vehicle.

Insulator: Any element or other material that will not conduct electricity. An insulator has five or more electrons in the valence ring.

Intake Air Temperature: The temperature of the air charge going into an engine. used to calculate air/fuel ratios in the PCM.

Intake Manifold: The part of the engine that contains passageways to direct fresh air into the engine. Fuel metering devices are often located in or on the intake manifold as well.

Intake Valve: The poppet type vale that opens to let air into the combustion chamber. An engine may contain 1 to 3 of these valves per cylinder, but two is the most common.

Integrated Motor Assist: A name used by Honda to describe their parallel hybrid drivetrain.

Intelligent Power Unit: The assortment of ECUs that control the motor/generator in the Honda IMA system.

Internal Combustion Engine: An engine that uses combustion to produce power where the combustion happens inside the engine.

Internal Permanent Magnet: The permanent magnet found a brushless A/C synchronous motor

Intrusion Beam: The horizontal beam found inside a car door that protects from intrusion of another car or anything else that might strike the door in a collision.

Inverter: An electronic device that converts A/C current into D/C current. 2. The device on a hybrid vehicle that converts and controls electricity in and out of the motor/generators.

IP: see Instrument Panel

IPM: see Internal Permanent Magnet

IPU: see Intelligent Power Unit

iVTEC: Intelligent Valve Timing Electronic Control. A system developed by Honda similar to VTEC but it also is capable of manipulating cam phasing. This will change the timing of intake and exhaust valve opening. Also see VTEC



Jack: A mechanic device used to lift a portion of a vehicle off the ground in order to make that part of the vehicle more serviceable.

Jack Stand: A stand used to support a vehicle after it has been lifted using a jack. A jack stand will securely lock in position as it supports the vehicle, a jack will not.

Jaguar: A British luxury and performance auto manufacturer founded in 1922. At one time it was owned by Ford, today it is owned by the Indian auto manufacturer Tata Motors.

JDM: Japanese Domestic Market. This applies to cars from Japanese manufacturers that are designed and intended for sale in Japan.

Jeep: An American automotive marque that evolved from the 4WD utility vehicles built for American troops during WWII. The exact origins of the name Jeep is a bit of a mystery. The military refered to the Jeep as a General Purpose or (GP).  Jeep has never been an independent manufacturer and have been built by many different companies over the years.

Jet: An interchangeable fuel metering orifice found in a carburetor. The size of the jet ultimately determines how much fuel is wasted, dumped, flushed…er, dispensed into the intake manifold through the venturi.

Jetronic: D, K, and L Jetronic systems were fuel injection system developed by Bosch in the 1960’s and 70’s. They are the grand daddies of the modern fuel injection systems used in all cars today.

Jounce: The upward movement of the wheels and suspension, or the downward movement of the chassis and body of the car.

Jump Start: A procedure used to provide power to a starter motor when the battery is dead and unable to provide enough power to crank the starter.

Junction Block: An electrical block where circuits connect to each other as well as connecting to fuses and relays.



K Car: A small front-wheel drive platform developed by Chrysler in 1981. While this platform proved to be unreliable and rather plain, it was inexpensive and fairly versatile. The K platform is credited with allowing Chrysler to come back from the brink of extinction after accepting government assistance in the early 80’s. The majority of Chrysler products in the 80’s were built on the K platform.

KAM: see Keep Alive Memory

Kamm Back: A type of automotive body design where the back of the car is long and tapered to increase aerodynamic efficiency. More often than not this design is just for looks and doesn’t offer much advantage for performance. The design was developed by an engineer by the name of Kamm.

Keep Alive Memory: Computer memory similar to RAM except it is nonvolatile. When power from the ignition switch is turned off the data in the memory is retained.

Keeper: A small steel wedge used in pairs to hold the valve spring on the engine valves in a cylinder head.

KERS: see Kinetic Energy Recover System

Keyway: A groove machined into a shaft where a woodruff key or some other key to lock a pulley in place on a shaft can be inserted.

Kia Motors: A Korean auto manufacturer founded in 1957. They are currently owned by Hyundai.

Kickdown: A transmission downshift that occurs when the accelerator is pressed to increase vehicle speed. The kickdown to a lower gear allow for more torque multiplication to help the vehicle accelerate.

Kilopascal: A unit of pressure used in the metric system and commonly used in the automotive world. 14.7 psi is equal to 100 kilopascals, or 1 atmosphere.

Kinetic Energy: The energy of an object in motion as determined by the mass and velocity of that object.

Kinetic Energy Recovery System: An electric motor generator system in parallel with the drivetrain that can recover energy through the use of regenerative braking. This is a term originating in auto racing seemingly because using the word “hybrid” would not inspire confidence in speed.

Kinetic Friction: Friction between two surfaces that move against each other.

Kingpin: A pivot point for steering used on a solid I-beam type front axle. The kingpin holds the knuckle to the axle and allows the knuckle to turn.

Knock Sensor: A sensor that can sense engine knock or detonation by picking up the vibration frequency that results from engine knock. the PCM uses this input to adjust timing advance.

Knuckle: The the cast or stamped metal piece behind the wheel assembly that holds the wheel bearing, brake system components, and allows for the attachment of the suspension and steering components.

KOEO: Key On Engine Off. A term used mostly by Ford to signify a self test performed with a scan tool with the key on and the engine off. Test failures will set a trouble code.

KOER: Key On Engine Running. A term used mostly by Ford to signify a self test performed with a scan tool with the key on and the engine running. Test failures will set a trouble code.

KS: see Knock Sensor



L4: An abreviation for a 4 cylinder engine.

Ladder Frame: A chassis design that uses a rigid frame made from two parallel beams with 5 or 6 cross members holding the beams together. Usually used in the build of pick up trucks and other heavy-duty vehicles.

Lambda: The difference between stochiometry and the actual air/fuel ratio. A lambda reading of 1 equals and air/fuel ratio of 14.7:1.

LamborghiniAn Italian manufacturer of super cars founded in 1964 based in Sant’Agata Bolognese. They are currently owned by Volkswagen and controlled by Audi. Manufacturing magnate Ferruccio Lamborghini started manufacturing cars after getting fed up with lack of good GT cars from Ferrari. Enzo Ferrari was more interested in racing, and Lamborghini thought racing was a waste. Lamborghini corporate offices are only about 22 miles from Ferrari.

Laminated Spring: A spring made up of several layers stacked on top of each other, leaf spring.

Lancia: An Italian auto manufacturer founded in 1906 and today owned by Fiat. Some Lancia models are just rebadged Chryslers sent to Italy.

Landau: A early model limousine kind of car with an open driver’s seat and an enclosed passenger area. That name originated int he days of the horse drawn carriage with a similar design. In the 1970s the term referred to any sedan or coupe that had a vinyl or simulated cloth roof.

Land Rover: A British manufacturer of four-wheel drive vehicles founded in 1948 with only one model simply called the “Land Rover.” Today they are combined with Jaguar and are owned by Tata motors of India.

Latent Heat: Heat that is exchanged during a change in state of some substance. It cannot be felt nor measured which makes it hidden. This term is used when describing the refrigeration action used in A/C systems.

Lateral Acceleration: The force that tends to push the vehicle sideways in a turn due to centrifugal force. Lateral acceleration can be overcome by application of the throttle halfway through the turn.

Lateral Grip: The cohesion of the tire when lateral forces want to push the tire sideways across the rolling surface.

Lateral Runout: The amount of side to side movement, or wobble in a wheel and tire assembly, or in a brake rotor. When found in brake rotors, a pulsation of the pedal may be felt when brakes are applied. A brake rotor can be machined to be returned to true. A tire assembly may need a new rim in order to be true.

Lateral Stability: The ability of a car to remain firmly pointed in a straight ahead direction. A vehicle that tends to wander back and forth lacks lateral stability.

Laws of Thermodynamics: 1. Energy can neither be created nor destroyed, it can only be made to change form. 2. Heat will only flow from something hot to something cold.

Lead: A connecting wire between multiple terminals

Lead: A soft, dense, semiconductive metal used in many electrical components and as a primary component in car battery construction.

Lead-Acid Battery: The common car battery comprised of 6 cells with a set of positive plates and a set of dissimilar negative plates, with a sulfuric acid electrolyte between the plates. These batteries have changed very little since they were invented in 1859.

Leaded Gasoline: Gasoline containing tetra-ethyl lead (TEL) as an octane booster. this gasoline was phased out in the 80’s as most cars started using catalytic converters which were ruined by lead fuel.

Leading Shoe: the front brake shoe in a servo action drum brake design.

Lead Sled: A style of custom hot rod from the 50’s characterized by the use of lead in the body work to smooth out many of the lines and other design features

Leaf Spring: A suspension spring made from 1 or more long flat springs stacked together. Typically mounted inline with the vehicle but sometimes mounted transverse to the vehicle.

Leak-Down Test: A test of engine cylinder integrity where compressed air is added to a cylinder at a regulated pressure, and the amount of air leaking form the cylinder is measured to determine if the cylinder is air tight enough to function properly with combustion pressures. More than 20% leakage is usually too much.

Lean Mixture: A air/fuel mixture that has more air than it should. Something greater than 14.7:1.

Lean-Burn: Combustion that takes place in an engine that is designed to run lean in order to save fuel and reduce emissions.

Lean NOx Catalyst: A special reduction catalyst used to reduce oxides of nitrogen in an oxygen rich environment such as that found in the exhaust stream of a diesel engine.

LED: see Light Emitting Diode

Left-Hand Drive: A configuration where the steering wheel is on the left side of the car designed for driving on the right side of the road, as opposed to the wrong side of the road like they do in Britain, and Japan, and other places that are islands. As if that has something to do with it.

Left-Hand Thread: a fastener with thread alignment that requires it be turned to the left to tighten. This is the opposite of how most nuts and bolts are built.

Lemon: A car that breaks down all the time. see British Cars.

LEV: Low Emissions Vehicle. A tier I emission standard given to qualifying vehicles in the 1990’s by the EPA.

Lexus: A Japanese luxury car manufacturer founded in 1989 for the U.S. market. Lexus is the largest selling luxury mark in the U.S. and Japan.

Light Emitting Diode: A solid state component that emits light as current passes though it. LEDs are quickly becoming the most common lights found on cars and trucks.

Li-Ion: See Lithium-Ion Battery

Li-Poly: see Lithium-Polymer Battery

Linesman’s Gloves: Nonconductive safety gloves worn by people working on high-voltage electrical systems. Gloves rated to 1000 volts must be worn by technicians working on hybrid and electrical vehicle systems. The inner glove is rubber to protect form the high voltage, and the outer glove is leather to protect the inner glove.

Liquefied Natural Gas: A form of natural gas used as a motor fuel. Natural gas is cooled to about -260° F to keep it in a liquid state. Being a liquid means that more fuel can be stored in a smaller tank than what would possible if the natural gas was in vapor form.

Liquid Petroleum Gas: Propane that is used to power an internal combustion engine in a motor vehicle.

Lithium-Ion Battery: A type of rechargeable battery that uses the transfer of lithium ions between the positive and nagtive plates to produce current. This is the kind of battery used in electric vehicles.

Lithium-Polymer Battery: A type of Li-Ion battery that uses a polymer electrolyte and is packaged in a thin plastic pouch to save weight. This battery is used in electric vehicles.

LNC: see Lean NOx Catalyst

LNG: see Liquefied Natural Gas

LNT: Lean NOx Trap, see NOx Adsorbing Catalyst

LPG: see Liquid Petroleum Gas

Load Tester: A piece of test equipment used to apply a heavy load to an electrical system to see if it is capable of supplying high current when needed. Load testers are used to test batteries and charging systems.

Lobe: An eccentric that rises or protrudes from a circular base. Used to affect some kind of mechanical movement such as that which a camshaft uses to open valves.

Longitudinal Mounted Engine: An engine that is mounted in the vehicle in line with the vehicle center line front to back. This is the way engines are mounted in rear-wheel drive vehicles, but it can be used for just about any type of drivetrain setup.

Low Side Driver: A driver within an ECU that controls an output by connecting the circuit to ground.

LSx: An abbreviation for any engine in the LS line of small block V8 engines built by General Motors.

Lubricity: The lubricating properties of a fluid, usually used when referring to fuel.

Lug, Wheel: The fasteners that hold the rim and tire assembly to the wheel hub. Most vehicles use a threaded stud pressed into the hub with a nut to retain the rim. Some cars use a bolt with a threaded hole in the hub.



M-85: Motor fuel that is 85% methanol and 15% gasoline.

Magnetism: A form of energy that exerts force on ferrous materials.

MAF: Mass Airflow Sensor. A sensor used by various computes to measure the amount of airflow into the engine. This is an indication of engine load as well as an indicator of how much fuel is to be blended with the air stream to maintain stoichiometry.

Mag Wheel: An old slang term used to describe custom wheel rims that were typically made from a magnesium alloy. this was before aluminum alloys became more popular.

Magna Flux: A test used to find cracks and steel and cast iron engine parts such as cylinder heads and engine blocks. This test is usually performed in a machine shop.

Magnum: A nonsensical term used to name engines found in Dodge trucks in the 90’s. Not sure if this is an engine or an ice cream bar but the marketing people said it was a good idea. see also, Triton, Vortec, iForce…and station wagon

Manettino: Italian word for “little lever.” The name for the small dial found on the steering wheel of F1 cars and modern Ferraris. The dial is used to change computer control settings for chassis and drivetrain systems.

Manufacturer’s Suggested Retail Price: The price on the Monroney label listing the price where you begin the wheeling and dealing with the car salesman with the bad comb-over.

Manual Transmission: A transmission that does not select gears automatically requiring the driver to select the proper ratio for the situation.

MAP: Manifold Absolute Pressure Sensor: A sensor used by various computers to measure positive and negative pressure in the intake manifold. This is an indicator of engine load or boost pressure.

Master Cylinder: The hydraulic actuator used in the transmission and multiplication of force to the hydraulic units at the wheels.

Master Cylinder, Quick Take-Up: A master cylinder that uses large and small diameter bores to move more fluid through a circuit that uses low drag calipers.

Mazda: A Japanese auto manufacturer founded in 1920. For a time Ford owned a controlling stake in the company until they sold out in 2010.

McPherson Strut: A suspension component that combines the spring with the dampener in one assembly. The combined unit makes for a very light-weight and compact design.

Mechanical Efficiency: The amount of forced produced at the crankshaft compared to the amount of force produced in the cylinders. Some energy produced by the engine is lost because that energy must towards driving the various components of the engine itself.

Mercedes-Benz: A German auto manufacturer owned by Daimler AG that traces its roots to the original motorwagen invented by Karl Benz in 1886. This car is thought to be the first automobile in the world. The Mercedes-Benz name did not appear until 1926. Mercedes is one of the leading auto manufacturers in the world, and one of the greatest luxury cars anywhere.

Mercury: An American car company founded by Ford in 1938 as an entry level luxury brand between Ford and Lincoln. Mercury was shutdown in 2011 due to financial difficulties which led the brand to offer nothing original in many years.

Metal-Oxide-Semicondictor Field-Effect Transistor: A more complex transistor design found in many electronic devices but specifically found in hybrid vehicle power inverter used to control the current to the motor/generators.

Metering Valve: A hydraulic control valve found on the front brake circuits of a vehicle equipped with disc brakes int eh front and drum brakes int eh rear. This valve delays front brake application slightly to allow rear drum brakes to apply at the same time as the front disc brakes.

Methanol: A wood alcohol often blended with gasoline to produce a motor fuel. Often used as fuel in race cars, methanol is very toxic to living things and very corrosive to fuel systems not designed for its use.

MG: see Motor/Generator

MIL: Malfunction Indicator Lamp. A generic term used to describe any lamp in the instrument cluster that illuminates in the event of a fault as found by any number of ECUs on the vehicle. check engine light, ABS light, airbag light etc.

Miller Cycle: A four-stroke cycle used in an internal combustion engine that has a shorter compression stroke by way of a delay in the closing of the intake valves. This is similar to the Atkinson cycle but a supercharger is used to keep volumetric efficiency high. This makes up for the loss of torque.

Misfire: The result of combustion when the fuel, spark, and compression are not happening as they should. This usually causes a shudder or stumble from the engine.

Mitsubishi: A massive Japanese industrial conglomerate who happens to manufacture cars on the side. After building ships for many years Mitsubishi decided in 1917 to start building cars. During WWII Mitsubishi was the company that built the “Zero” for the Japanese Air Force.

MLS: see Multilayer Steel gasket

Monitor: A system test run by the PCM to examine it’s own operation. On vehicles equipped with OBDII the monitors are very specific and defined by EPA regulations. A monitor will not run until “enable criteria” are met.

Monocoque: A car body structure that does not require a frame because rigidity is built into the way the various pieces of steel are bent and joined together. This is the most common body design today, found on a cars and many light trucks. Sometimes referred to as unibody or unitized chassis.

Monroney Label: The window sticker found in a new car that details the vehicle specifications and all the legal mumbo jumbo. Named after Senator Mike Monroney from Oklahoma who was a sponsor of the federal legislation that mandated disclosure of new car information in this format.

Moonroof: Any car roof that has a sliding panel that can move back over or into the rest of the roof panel to open up the cabin to the outside. see Sunroof.

MOSFET: see Metal Oxide Semiconductor Field Effect Transistors

Motor/Generator: The electric drive unit found in an HEV that is capable of being either a motor or a generator depending on what is needed. This is a term that originated on Toyota hybrid systems.

MSRP: see Manufacturer’s Suggested Retail Price

MT: see Manual Transmission

Muffler: A sound dampening device in the exhaust system that blocks engine noises from leaving the tailpipe without blocking exhaust gases.

MultiAir: A proprietary term used by Fiat to describe the air induction system on their new line of engines used in the Fiat 500 here in the U.S.. The MultiAir system does not require a throttle plate nor does it use a camshaft to operate the intake valves per se. Intake valve modulation is performed via hydraulic actuators driven by the cam on the exhaust valve side of the head. These actuators use engine oil to produce the pressure that will operate the intake valves. The oil pressure is then controlled by electronic solenoids to determine when the valves open and for how long. This eliminates the need for a throttle because the intake valves can be opened for a very short time to keep the engine at idle, and for a very long time to let the engine rev.

Multilayer Steel Gasket: A gasket made from several thin layers of steel gasket stacked on top of each other or laminated together. Commonly used for modern head gaskets.

Multiorifice Nozzle: A term used to describe an injector nozzle for a diesel injector that used multiple orifices to spray fuel. Usually used on direct injection fuel systems.

Multi-Port Injection: The type of fuel injection found on most cars on the road today characterized by the use of a separate injector at each intake port, praying fuel onto the back of the intake valves.



N2O: see Nitrous Oxide

NAC: see NOx Adsorbing Catalyst

NADA: see National Auto Dealers Association

NASCAR: see National Association for Stock Car Auto Racing

NATEF: National Automotive Technicians Education Foundation. An accrediting organization for automotive training programs. Community colleges and other automotive training schools must prove they educate automotive technicians to high standards to gain accreditation through NATEF.

National Automobile Dealers Association: An advocacy organization for auto dealers. They are probably most well known generally for their used car pricing guides.

National Highway Traffic Safety Administration: A redundant government agency that is responsible for making sure you don’t hurt your precious little self driving your 6000 lb. land missile of death.

Natural Aspiration: A term used to describe engine induction systems that do not use any kind of system to boost air pressure entering the engine. I.E. they do not have a turbocharger or supercharger.

National Association of Stock Car Auto Racing: The largest sanctioning body in North America for stock car racing. NASCAR is the also the largest spectator sport in the world. It is the largest venue for mullets in the world.

Navi: A slang term for satellite navigation system.

Needle and Seat: A fuel control mechanism found above the float bowl in a carburetor to control the flow of fuel into the float bowl. As the fuel level rises the float closes off the needle and seat.

Negative Charge: An electrical charge that carries excess electrons. This is found in the ground side of a circuit.

Negative Terminal: The battery terminal with the negative charge. This is the terminal where no voltage potential can be measured. This is the most negative point in all of the vehicle electrical systems.

Neutral Safety Switch: A switch in the starter activation circuit that only allows the starter to crank when the transmission is in park or neutral.

Neutron: A subatomic particle found in the nucleus of an atom that has a neutral charge.

NG: Natural gas. Used as an alternative fuel to gasoline.

NGV: Natural Gas Vehicle. A car or truck with an engine capable of using natural gas as fuel.

NHTSA: see National Highway Traffic Safety Administration

Nissan: A Japanese auto manufacturer founded in 1933 and based in Yokohama, Japan. Nissan came from the Datsun company which evolved over the years starting in 1911. When Nissan came to the U.S. they sold cars under the Datsun name beginning in 1959. Eventually they got rid of the Datsun name in the mid-80’s, but have recently brought it back for cars sold in emerging markets. Nissan is currently owned by Renault.

Nitrous Oxide: A chemical used to increase oxygen intake to the combustion chamber. N2O breaks down into oxygen and nitrogen. This adds a tremendous amount of oxygen to the combustion chamber which means the engine can then burn more fuel and make more power.

Noid Light: A small lamp that can be plugged into a fuel injector harness to check whether or not the PCM is grounding the injector. Noid is short for solenoid which is essentially what a fuel injector is.

Noisy Pedal: A slang term for gas pedal.

Nonattainment Area: A region where air pollution exceeds standards set by the EPA for a given pollutant. Local authorities in these areas must implement measures to bring air quality back into compliance. This is when vehicle emissions testing usually begins.

Nonindependent Suspension: Any suspension design where both wheel on one axle are attached to the same solid inflexible axle member.

Normally Aspirated: An engine that does not use any forced induction system such as a turbocharger or supercharger.

NOx: See Oxides of Nitrogen

NOx Adsorbing Catalyst: A diesel exhaust after-treatment catalyst used to break down NOx in the exhaust emissions. The NAC was mostly used as a precursor to diesel exhaust fluid systems and was found to not be very effective compared to DEF. The NAC required injection timing that was retarded so much the engine ultimately saw a decrease in power output and diminished fuel economy.

NOx Sensor: Used to detect NOx levels in diesel after-treatment systems in order to monitor various systems that are there to reduce it.



O2 Sensor: see Oxygen Sensor

OAT: see Organic Acid Technology

OBDI: On-Board Diagnostics I. The default name for the original OBD systems found on vehicles with electronic controls between the early 80’s and 1995.

OBDII: On-Board Diagnostics II. The federally mandated standard for OBD system found on all vehicles from 1996 to the current year. This standardized OBD across all makes and models.

OCS: Occupant Classification System. Part of more advanced airbag restraint systems, OCS is capable of detecting how large a person might be and commanding airbag deployment accordingly.

Octane: The eighth longest hydrocarbon chain, commonly used in gasoline formulations. High octane fuel contains more octane which gives it more desirable anti-knock qualities.

Octane Rating: Gasoline. The measure of the fuel’s ability to resist combustion under heat and pressure alone.

Ohm: The unit of measured resistance in an electrical circuit or component. Named for German physicist Georg Simon Ohm.

Ohmmeter: A tool used to measure resistance or measure the ohms of an electrical circuit.

OHC: see Overhead Cam

OHV: Overhead Valve. A valvetrain design that uses intake and exhaust valves mounted above the piston in the cylinder head, but uses a single camshaft mounted in the block to operate the valves via push rods.

Oil Breakdown: The gradual degradation of engine oil that results from heat and pressure in the engine. Oxidation is the leading form of oil breakdown.

Oil Burner: A slang term used to describe a diesel engine or vehicle.

Oil Control Ring: The bottom set of rings found on the piston. These rings sweep the cylinder walls to keep engine oil from getting up past the compression rings. If oil get past those rings it will burn in the combustion chamber.

Oil Cooler: A heat exchange device used to keep engine oil cool. Some are located inside the radiator and some are like a small separate stand-alone radiator. Not all vehicles are equipped with oil coolers.

Oil Filter: The filter that removes debris and contaminants from the engine oil. This should be replaced whenever the engine oil is replaced.

Oil Gallery: The main oil supply lines through the engine block.

Oil Pan: The pan that encloses the oil sump below the crankcase. The pan contains a drain plug where oil is drained during an oil change service.

Oil Pump: The pump within the engine that is responsible for moving the oil through the engine. The pump is usually driven y the crankshaft directly but it may also be driven by the camshaft.

OL: see Open Loop

Oldsmobile: An American auto manufacturer founded by Ransom E. Olds in 1897. It was one of the oldest car companies in the world until it was shut down by GM in 2004. GM had acquired Oldsmobile in 1908 and positioned them as a near luxury brand for most of its existence.

Open Loop: Control programming in the PCM that used to control air/fuel ratio before the O2 sensors get warmed up and start functioning. O2 sensor output is ignored during open loop. see Closed Loop

Organic Acid Technology: A chemical additive found in GM Dex-Cool that uses a carbon based based molecule to give the coolant longer life.

Oscilloscope: A piece of test equipment used to graph voltage and amperage over time. This allows a technician to examine fluctuations in electricity in a circuit to determine if things are functioning properly.

Otto Cycle: The common four-stroke cycle used by most internal combustion engines consisting of the following strokes, intake compression, power, exhaust. Invented by a Frenchman named Nikolaus Otto in 1864.

Overhang: The distance between the front of the front tire and the front of the car, or the distance between the back of the rear tire and the back of the car.

Overhead Cam: A valve train design that uses a camshaft mounted in the cylinder head to more directly operate the valves, as opposed to have a cam mounted down in the block.

Oxidation: A chemical reaction that allows oxygen to bond with something unintentionally. When this happens the properties of the substance being oxidized changes. Steel body panels turn to rust when the iron in them oxidizes.

Oxides of Nitrogen: Various forms or combinations of nitrogen and oxygen such as Nitric Oxide and Nitrogen dioxide. These gases are pollutants emitted from internal combustion engines. they form the basis for photochemical smog.

Oxygen Sensor: The primary feedback sensor for the PCM showing air/fuel ratio. The Oxygen sensor is mounted in the exhaust system where it detects oxygen content in the exhaust gases. Too much oxygen means the PCM is not providing enough fuel, too little oxygen means the PCM is providing too much fuel.

Oxygenated Fuel: A fuel that is blended with a oxygenate to aid in the oxidation of the fuel that occurs during combustion. Gasoline blended with 10% ethanol is considered oxygenated. The oxygen in the ethanol helps the gasoline to burn more cleanly.

Ozone: O3. An oxygen molecule with three atoms that exists naturally in the stratosphere to filter out UV radiation. Ozone can form at ground level from a reaction between NOx and sunlight. At ground level it is a powerful lung irritant.



PAG: see Polyalkylene Glycol

Pagani: Super car manufacturer based in San Cesario Sul Panaro, Italy. Founded in 1992 by Argentinian born Horacio Pagani, as a manufacturer of carbon fiber body panels. Pagani started out working for Lamborghini but when they showed no interest in the carbon fiber in which Pagani believed, he went out on his own. Pagani built their first car, the Zonda C12 in 1999. Pagani headquarters is located about 6 miles from Ferrari and 7 miles from Lamborghini.

Panhard Rod: A rigid bar that attached to the vehicle frame on one side of the vehicle, and the live axle assembly on the other side of the vehicle. The panhard rod keeps the axle assembly centered and prevents lateral movement of a live axle. First used by the Panhard Automobile Company of France.

Park Brake  The brakes that are used to hold the vehicle stationary when parked. The lever or mechanism the driver uses to apply the park brake.

Parallelogram Steering Linkage: A linkage used with a recirculating-ball steering gear that has a center link connected between a pitman arm and an idler arm, with tie rods on each end. The center link always stays parallel to the frame of the vehicle where the pitman and idler arms attach. When steering left or right the several links always form a parallelogram.

Parameter Identification: the term used to describe each separate piece of information found in a scan tool datastream. Each PID refers to some kind of operating condition.

Parking Pawl: A small finger-like wedge that gets lodged against the teeth of the parking gear in an automatic transmission in order to bind up the output shaft and provide the park feature of the transmission.

Particulate Matter: Small solid particles of waste found in the air resulting from vehicle use. Some PM comes from vehicle exhaust, some PM comes from tires and brakes. These particles can be harmful when found in the air we breathe.

Passive Regeneration: A regeneration process for the a DPF where the PCM can cause regeneration ot occur under normal driving conditions once enable criteria are met. This regeneration will burn the collected soot out of the DPF so that is may then keep collecting these particulates to prevent them from leaving the tailpipe.

Passive Restraints: A passenger restraint system that does not require any action on the part of vehicle occupants to function. This like airbag systems or automatic shoulder straps are passive restraints.

PCU: see Power Control Unit

PCV: Positive Crankcase Ventilation. An emissions control system that recirculates crankcase gasses into the intake rather than expelling them out into the air.

PDK: see Porsche Doppelkupplung

Pent-Roof Combustion Chamber: The most efficient combustion chamber designed currently used by all auto manufacturers. Evolved from the hemispherical combustion chamber, the pent-roof allows intake and exhaust valves to tilt away from each other which makes for better flow through the combustion chamber. This design also allows for more and bigger valves. Most pent-roof designs use 4 valves per cylinder.

PEFC: Proton Electrolyte Fuel Cell, another name for a Proton Exchange Membrane fuel cell.

PEM: see Proton Exchange Membrane

Petroleum: Another name for crude oil

Phaeton: An open top vehicle with four doors. This term originated in the days of the horse-drawn carriage, many uses today don’t really follow the original definition.

PHEV: Plug-in Hybrid Electric Vehicle. A hybrid vehicle that typically has 10 to 50 miles worth of electric only range with an option to plug-in to an electrical outlet to charge the batteries. This is the kind of hybrid the Chevy Volt is. They try to say it’s an electric car but it is a hybrid.

PHT: see Parallel Hybrid Truck

PID: see Parameter Identification

Pillar: A structural member that supports the roof of the car. Many times using letters to designate which pillar, e.g. A, B, C, D.

Piston: Engine part. The piston moves up in the cylinder to compress the air/fuel mixture before combustion. When combustion occurs the piston transmits that force downward against the connecting rod in order to turn the crankshaft.

Pitman Arm: A piece of steering linkage that connects the steering gear to the the rest of the steering linkage. Usually used in conjunction with a recirculating-ball steering gear.

Planet Carrier: The part of a planetary gearset that houses the planet pinions.

Planetary Gearset: The gears in most automatic transmissions that make the various gear ratios possible. The gearset contains a sun gear in the center, planets the rotate around the sun, and a ring gear that contains them all. One gear is held and another is driven, while the third becomes the output. One simple planetary gearset can provide up to 5 forward speeds and two reverse gears.

Plenum: The common chamber in an intake manifold behind the throttle plate. 2. the common air chambers within the air handling box of the HVAC system.

P-L-N: see Pump-Line-Nozzle

Plymouth: One of the now defunct former divisions of Chrysler. Plymouth was the entry-level brand from Chrysler ever since its founding in 1928. For the last several years of its existence Plymouth had nothing unique from other Chrysler brands with the exception of the Prowler (which was weird and underdeveloped). Plymouth shut down in 2001.

PM: see Particulate Matter

PM Generator: Permanent Magnet Generator. A type of sensor usually used to measure speed or position of a rotating shaft. A reluctor is passed near a permanent magnet with a coil around it. Reluctor teeth cause a fluctuation in the magnetic field which induced a small A/C current into the conductor. The current becomes a signal that is interpreted by the computer.

Polyalkylene Glycol: A synthetic lubricant compatible with R-134a refrigerant and used as compressor oil in A/C systems.

Polymer: A word used to describe plastic when you want to sound really smart.

Pontiac: An American car company founded by GM in 1926. Pontiac was marketed as a companion brand to Chevrolet for most of it’s existence, in the U.S. they were sold as a performance variant of similar Chevy models. Pontiac was shutdown in 2010 as part of GM’s bankruptcy restructuring.

Porsche: A German auto manufacturer founded in 1931 by Ferdinand Porsche, and based in Stuttgart, Germany. Ferdinand Porsche is one of the greatest automotive engineers of all time. He designed the original Volkswagen Beetle although he did not found the Volkswagen company. Porsche uses a “Springende Pferd” in their logo much like the “Cavallino Rampante” used by Ferrari.

Porsche Doppelkupplung: (PDK) The name used by Porsche for it’s dual-clutch transmission. Doppelkupplung literally means “double clutch.”

Post-Combustion: The period of time after the air/fuel mixture has burned. 2. An emissions control device that affects or reduces emissions after combustion has occurred and potential pollutant are formed. A catalytic convert is a post-combustion emission controller.

Potential Energy: Energy that is not in use but can be when the time is right. Gasoline in the fuel tank has potential energy that is unlocked during combustion.

Power Control Unit: Part of the inverter found in Honda hybrid vehicles, the PCU specifically controls current to the motor/generator.

Powertrain: Everything from the engine to the wheels that are responsible for making the car go. Sometimes used just to describe the engine and transmission together as one unit.

Power Valve: a valve found inside a carburetor that allows more fuel to flow into the throttle body when the engine is under heavy load.

Pour Point: The lowest temperature at which diesel fuel can still be poured like a liquid. This usually around -35° F.

Precombustion Chamber: Prechamber. A chamber found on an internal combustion engine where the combustion process begins before moving outward into the main combustion chamber. This system is used on indirect ignition diesel engines but it is also used on some gasoline engines in the past.

Preignition: A condition where something in the combustion chamber ignites the air/fuel mixture prematurely. This can be cause by overly advanced ignition timing or hot spots in the chamber.

Programmable Read Only Memory: A PCM memory chip which contains the base instructions for operation of the engine. Used on older vehicles with fuel injection back in the 80’s and 90’s. The PROM could be easily replaced in order to give the PCM a new set of instructions.

PROM: see programmable read only memory, not that silly dance you never went to in high school.

Proportioning Valve: A hydraulic control valve found in the rear brake circuit on a vehicle equipped with disc brakes int he front and drum brakes int he rear. This valve reduces hydraulic pressure to the rear brakes to prevent them form locking up. Drum brakes produce more stopping power initially than disc brakes so pressure must be reduced so all brakes apply more evenly.

Proton Exchange Membrane: A type of fuel cell used to move current through an electrical load using hydrogen. The fuel cell separates the proton in hydrogen from the electron and doesn’t let them rejoin until the electron flows through a circuit load.

P/S: Power Steering. A system that makes turning the steering wheel easier for the driver.

PTOX: Particulate Trap with Oxidation Catalyst, see Diesel Particulate Filter

Pulse Width: an electrical control method defined by the the total on time measured in milliseconds. Fuel injectors are pulse width modulated.

Pump-Line-Nozzle: A type of diesel fuel system that uses a central pump driven by a geartrain from the crankshaft that distributes fuel to each cylinder based on the speed and load of the engine. This was invented by the Bosch company in the 1930’s and it made the diesel engine a viable power source for motor vehicles.

Pumpkin: A slang term used to denote the differential on a live axle. The bulge of the differential in the middle of the axle housing resembles a pumpkin.

Purge Solenoid: Part of the EVAP system. The electronically controlled valve used to vent gasoline vapors captured in the fuel tank, into the intake manifold where they can be pushed into the combustion chambers and burned with the air/fuel mixture.

Pushrod: A rod found in cam in block engine designs that transmits the force form the camshaft and lifter mechanism up to the rocker arm to open open the valve. This is an old inefficient way of opening valves but a few manufacturers still use this method.



Quad 4: A 2.3 liter I4 engine developed by GM in the late 80’s and used in various models until 2002. The engine represented a breakthrough for GM as it had 4 valves per cylinder and DOHC. This was the first such engine mass produced by GM.

Quad Cab: Dodge terminology for a four-door pickup.

Quad-Cam: A DOHC engine that is a V or horizontally opposed.

Quad Driver: A module within an ECU containing 4 drivers that control 4 outputs.

Quadrasteer: A term used by GM to describe the 4WS system found on some of their trucks and SUVs.

Quadricycle: Henry Ford’s first car. Any early automobile that was like a four wheel bike with a motor.

Quarter Panel: the body panel around the wheel, sometimes called the fender.

Quarter Window: A small hinged window in the front door that open by rotating in place. Used to be very common on old cars.

Quattro: A term used by Audi to describe any of their vehicles equipped with all-wheel drive.

Quench Area: An area in the combustion chamber where the top of the piston at TDC is very close to the top of the cylinder head. The fuel and other gases in this area are kept away from the flame front that results from the combustion process, subsequently these gases don’t get burned and lead to inefficiency. More modern combustion chambers eliminate quench areas which improves fuel economy and lower emissions.

Quenching: The cooling of gases that results from compressing them into a narrow passage away from heat sources in a cylinder. This is to keep them from igniting prematurely.

Quick Connect: Fittings used to attached pressurized liquid and vapor lines. They typically snap together easily but require a special tool to disconnect.



R-12: Refrigerant 12. chemical name: dichlorofluoromethane. The type of refrigerant used in automotive A/C systems until the 1994 model year. R-12 is a chlorofluorocarbon which is thought to have caused a hole in the ozone layer so international treaties phased out the production and use of R-12 in the early 80’s.

R-1234yf: Refrigerant 1234yf. Chemical name: terafluoropropene. This refrigerent is used in cars in Europe and in a few new models in the U.S., but so far is not mandated in the U.S. It is a hydrofluoroolefin and has a small global warming potential compared to R-134a which is the reason it is being used. This new refrigerant is not without controversy because it has been shown to be flammable under the right conditions.

R-134a: Refrigerent 134a. chemical name: tetraflouroethane. The refrigerant used in automotive air conditioning systems since 1994, when R-12 was phased out. R-134a is a hydrofluorocarbon and is therefore not harmful to the ozone layer if leaked out of the system. However, it is said to be a greenhouse gas and has been replaced in Europe with R-1234yf

Rack-and-Pinion Steering: A steering gear that utilizes a pinion gear on the end of the steering shaft, that engages a rack gear within the long narrow housing. The tie rods are attached to the ends of the rack gears. This design is compact, light-weight and probably the most common configuration on cars and trucks today.

Radiator: The primary heat exchanger found in the engine cooling system, mounted at the front of the car behind the grill. The radiator is comprised of several narrow passageways and tubes surrounded by very thing fins for transferring heat to the surrounding air.

RAM: Random Access Memory. Used in computer processing within various control modules, can be read and written to freely by the processor. RAM is volatile and will be erased when the computer or vehicle is turned off.

Rate Shaping: The variable injection rate control that occurs during the injection event on a diesel engine. Rate shaping affects the way the fuel burns.

Rear Main Seal: An oil seal located at the back of an engine that seals pressurized oil in the rear main bearing assembly.

Rear-Wheel Drive: A drivetrain configuration that uses the rear wheels only to propel the vehicle. Often thought to be the best and purest way to drive a car for enthusiast driving.

Recall: A campaign by an auto manufacturer to repair a problem that has come to light after the release of a model. Safety recalls can be mandated by the NHTSA.

Receiver-Drier: A component in the air conditioning system found in the high pressure side designed to remove moisture from the refrigerant.

Recirculating-Ball Steering: A steering gear that uses a sliding piston that is moved back and forth in the gear housing by recirculating small steel ball-bearings around the outside. The piston engages the sector shaft which sticks out through the housing and has the pitman arm attached to it. The rest of the steering linkage is usually a parallelogram, or cross-steer style linkage.

Rectification: The process of converting A/C into D/C.

Rectifier Bridge: The component found in an alternator that uses diodes to change the A/C output of the stator into D/C that can be stored in the battery.

Redline: The maximum speed at which an engine can turn before mechanical limits are breached. An engine running at redline or above can suffer major and sudden failure.

Regenerative Braking: A technique used by all hybrid vehicles whereby kinetic energy that is normally wasted during braking is converted into electricity to be stored in the HV battery. This is accomplished by the mass of the vehicle rotating the MG assemblies as generators which uses up the dynamic inertia of the vehicle. Blah blah blah.

Relay: An electrical switching mechanism that allows a small amount of current to control a large amount of current. This cuts down on the amount of heavy gauge wire needed to supply current to high wattage circuits.

Reluctance: The measure of somethings ability to resist magnetic flux lines passing through itself. 2. That uneasy feeling I always had when I asked a girl out.

Reserve Capacity: The amount of time a battery can be discharged at a certain rate without the voltage dropping below a specified value. This is one way in which batteries are rated.

Resistance: Electrical. Anything that restricts the flow of current through an electrical circuit. Unwanted resistance exists in the form of corrosion, damaged wires, loose connections, and faulty components. Normal resistance exists in the load device or component within the circuit.

RFI: Radio Frequency Inference. The reason that an ignition misfire can sometimes be heard on the AM radio in your car.

Rheostat: A variable resistor with two terminals used to regulate the flow of current in a circuit.

Ring-and-Pinion: The primary gears in a differential that transfer the rotational force of the driveshaft 90 degrees into the axle.

Road Load HP: The amount of horsepower a vehicle needs to maintain a steady speed with a consistent load. In most cases this will be far less than what the engine is capable of producing.

Roadster: Traditionally, a two seat, two door car with no roof and usually no side windows. In modern parlance it is any convertible sports car.

Rocker Arm: A mechanism that transfers the forces of the pushrod to the top of the valve stem in order to push the valve open.

Rocker Panel: The area of the body below the doors. Many cars don’t have much of a rocker panel anymore.

ROM: Read Only Memory. Memory that is programmed and cannot be written to by the computer. ROM contains the basic operating instructions for the computer and cannot be changed without changing the chips set which contains the ROM.

Room Temperature Vulcanizing: A common aerobic sealant which will cure in at ambient temperatures and within the presence of oxygen.

RPM: Revolutions Per Minute. Used to describe engine operational speed.

RTV: see Room Temperature Vulcanizing

Run Flat Tire: A tire that can be run with 0 psi air pressure without damaging the tire or rim. This type of tire has a very stiff sidewall that can support the weight of the vehicle when air pressure is lost. Some have a solid core mounted around the center of the rim that does the same thing.

RWAL: Rear Wheel Anti-Lock. A system that provides anti-lock brakes for the rear wheels only. This is to keep the rear wheels from sliding sideways under heavy braking.

RWD: see Rear-Wheel Drive



SAE: Society of Automotive Engineers. This is a trade group made up of engineers from around the world who set design standards for the industry. They are often consulted by manufacturers as well as world governments for clarification of automotive technology and design capacities.

SAI: see Steering Axis Inclination

Scan Tool: An electronic diagnostic tool that allows technicians to tap into the inner workings of a computer on-board the vehicle. Typically used to read DTCs and examine serial data.

Schrader Valve: A valve used to retain some fluid substance in an enclosed system while also allowing easy access to the fluid. A simple tire valve is a type of schrader valve.

Scion: A line of entry-level vehicles manufactured by Toyota and specifically marketed for the 16 to 25 year-old demographic. Scion was launched in the U.S. in 2004 with marketing designed to appeal to generation Y.

SCR: see Selective Catalyst Reduction

Scrub Radius: The difference between the point where the steering axis intersects the road and the center-line of the tire contact patch intersects the road. this affects steering effort and feel.

Scuderia: Italian word for “stable” as in a place where a horse lives. Used to describe a racing team, Scuderia Ferrari for example, the name of the Ferrari racing team started by Enzo Ferrari long before he began building cars.

Sedan: A type of car with 4 doors, a solid roof, and a trunk.

Selective Catalyst Reduction: A diesel emissions reduction or after-treatment system responsible for reducing oxides of nitrogen in the exhaust. SCR uses a diesel exhaust fluid composed of urea to breakdown NOx. This DEF must be added to the vehicle in a separate tank from the fuel.

Service Brake:  The brakes that are used to slow the vehicle or bring it to a stop.

Service Engine Soon: see Check Engine Light

SES: see Service Engine Soon

Shift Gate: The shift pattern that the lever follows. This is usually determined by an internal mechanism. On some vehicles with manual transmissions the shift gate will be determined by an external mechanism. This type of gated shifter makes for very precise shift patterns.

Shift Lever: The transmission lever used to select a gear. This device is disappearing on automatic transmissions in favor of electronic buttons and selectors.

Shimmy Shock: A slang term to describe a steering dampener found on vehicles with a solid front axle. The dampener is meant to handle steering kickback, or shimmy, and it usually works just like a normal shock absorber.

Shock Absorber: A suspension spring dampening assembly mounted independent of the spring.

Shooting Brake: A two door station wagon, usually combining attributes of a station wagon and a sport coupe. Sometimes used by people who actually own station wagons to describe their car when they don’t want to feel like a nerd. The term originates as a horse-drawn carriage used to carry hunting (shooting) parties and their supplies.

SI: Spark Ignition. A method for igniting fuel in the combustion chamber. Normal cars and truck use this method.

Skid Pad: An automotive test track used to measured handling ability of a vehicle. This such as road holding ability and lateral G forces are measured on a skid pad.

SkyActiv: A term used by Mazda to describe new technologies used in some of their models to increase efficiency. Most of these technologies are related to the use of high-compression engines, more efficient turbo designs, and lighter weight materials.

Slushbox: A slang term for automatic transmission

Small Block: An engine block, typically a V8, that is built using a smaller block than similar engines from the manufacturer that are built using a big block. The difference between these two has nothing to do with displacement, only the overall dimensions of the engine block. Head designs can vary substantially.

Smog Pump: A slang term used to describe the AIR Pump. This is the heart of the emissions control system that injects air into the exhaust in the exhaust manifold and into the catalytic converter to oxidized CO and HC.

Snap On: An American tool manufacturer based in Wisconsin that builds tools commonly used by automotive technicians. They are credited with inventing the modern ratchet with interchangeable sockets.

SOHC: Single Overhead Cam. A valve train design that uses a single camshaft mounted in the top of the cylinder head to operate both intake and exhaust valves. SOHC is considered more volumetrically efficient as OHV designs but not as efficient as DOHC designs.

Solenoid: An electromechanical device that is used to control liquids, vapors, or mechanical actions in various systems in the automobile. Fuel injectors are solenoids

Spark Plug: A device that allows a place for the ignition spark to manifest within the combustion chamber. The spark jumps an air gap from one electrode in the spark plug tip to another. The ionization that takes place in the gap causes the plugs to slowly wear out over time.

Spindle: The horizontal shaft on which a wheel bearing or hub assembly might be mounted, usually attached to a knuckle.

Spoiler: A raised bar along the back of the vehicle usually on the trunk lid. On some high-performance cars this serves the function of improving down-force on the drive wheels by spoiling airflow over the car that tends to cause lift. On something like a mid-nineties Honda Accord is was simply a styling que that is now totally out of style.

Spur Gear: A gear with thick cut teeth that are parallel to the center axis. This gear in inexpensive but very noisy in operation. Some cars with a manual transmission make a whining noise in reverse because the reverse gears are spur gears.

Spyder, Spider: A term used by European auto manufacturers to describe any two seat convertible. The term comes from the days of the horse-drawn carriage. A small, lightweight two seat carriage was known as a spyder.

Squib: a pyrotechnic device that burns but does not explode in order to set off a larger charge. Airbag inflators use a squib to start the inflation process.

SRS: Supplemental Restraint System. Mechanisms other than seat belts that will restrain the occupants of the vehicle in the event of a collision, typically airbags.

Starter: An electric motor used to start the gasoline engine. The starter is activated via the ignition switch.

Station Wagon: Any vehicle that does not have trunk behind the back seat but has a larger cargo area and a rear hatch through which cargo can be loaded, it might also have a third row of seating in this area. These were really popular in the U.S. back in the 80’s but fell out of favor when the minivan was invented. In the modern-day this is essentially what the cross-over is but don’t tell people who drive a cross-over that they have a station wagon even though they do.

Stator, Alternator: The stationary windings found in an alternator where current is induced. Three windings are used to create a three phase A/C current which will be rectified to D/C before it leaves the alternator.

Steer Ahead: The last adjustment made on a live axle steering setup such as cross-steer linkage, to ensure the steering wheel is level when the vehicle is tracking straight. This is usually performed by adjusting the drag link.

Steering Axis Inclination: The inward or outward tilt of the steering axis when viewed from the front or the back. This angle is similar to caster in that it helps return the wheels to center after a turn.

Steering Column: The assembly extending from the dash where the steering wheel is found. The device may also house many other vehicle controls.

Steering Damper: A device in the steering system that is meant to absorb shock that can be transmitted from the road up through the steering linkage to the driver. Sometimes it takes the form of a standard shock absorber, and sometimes it is nothing more than a rubber bushing on the steering shaft.

Steering Gear: The assembly of gear that transmit the rotational input from the steering wheel to the side-to-side motion needed to rotate the wheels that steer the vehicle. Usually rack and pinion or recirculating ball.

Steering Geometry: Variables in the various steering angles that have a major affect on steering feel and vehicle handling. This includes things like camber, caster, toe, etc.

Steering Kickback: Harsh feedback felt in the steering wheel as front wheel strike obstacles on the road. Obstacles hit the front wheels and force them to turn and this motion is transmitted up through the steering system. This is usually common on steering systems with a solid front axle.

Steering Lock: The mechanism in the ignition switch cylinder the locks the rotation of the steering wheel when the key is removed or car is parked. 2. The point of steering wheel rotation where the wheel cannot be turned any farther.

Steering Rack: A steering gear assembly that uses a rack and pinion design.

Steering Ratio: The gear ratio in the steering gear assembly that will ultimately determine how quickly the wheels turn to how much input is provided at the steering wheel.

Steering Shaft: The shaft that connects the steering wheel to the steering gear through the middle of the steering column.

Steering Wheel: If you need this word defined for you, you better not be getting behind this thing.

Steering Wheel Centering: An adjustment made to front wheel alignment to ensure that the steering wheel will be level when the vehicle is tracking straight ahead.

Steering Wheel Puller: A tool needed to remove a steering wheel from the steering shaft on applications where the wheel is press-fit.

Stepper Motor: An electric motor that can move in tiny increments or steps. This is typically used for idle air control motors on fuel injected engines.

Sterling: A subsidiary of Rover that sold rebadged Hondas in the U.S. during the late 80’s and early 90’s.

STFT: see Short Term Fuel Trim

STI: see Subaru Technica International

Stoichiometry: A balanced ratio of reactants needed in a chemical reaction. The stoichiometric air/fuel ratio for combustion in a gasoline engine is 14.7:1.

Stradale: An Italian word that means “road going,” typically used to name the street version of a car built for the track.

Strike Out Bumper: A rubber or poly-urethane bumper that keeps suspension components from touching abnormally when the suspension bottoms out. see Bump Stop

Stroke: The distance the piston travels in the cylinder from BDC to TDC.

Strut: see McPherson Strut.

Subaru Technica International: The motorsport division of Fuji Heavy Industries that is always associated with the Subaru brand.

Suicide Door: A car door that is hinged at the rear.

SULEV: Super Ultra Low Emissions Vehicle. A tier I emission standard given to qualifying vehicles in the 1990’s by the EPA. Cleaner than ULEV, not as clean as ZEV.

Sump: The area below the crankshaft where the oil drains and sits when not circulating. see dry sump.

Sunroof: Any car roof that has a glass panel that allows light to enter the cabin. see Moonroof.

Supercharger: A forced induction system that uses a compressor to force more air into the intake manifold allowing an engine to use more oxygen and produce more power. Superchargers are driven by a belt from the crankshaft.

Superleggera: Italian for “super light-weight.” This term is used by European manufacturers to describe special edition models that are built to be very light-weight. Reducing weight makes any car faster.

Sway Bar: see Anti-Roll Bar

Synchro, Synchronizer: A ring found between gears and output shaft hubs that is tapered on the inside. As the transmission shifts to a new gear the synchro will match the rotational speed of the selected gear to the speed of the output shaft so no grinding will occur. Very old manual transmissions were not synchronized so they had a tendency to grind more often if not driven properly.



T-Top: A type of car roof with removable panels above the driver and passenger. Each panel is separate from the other and when both are removed a bar or support will remain between the top of the windshield and the back portion of the roof. T-tops are common on American sports cars from the 70’s such as the Camaro and Mustang because with the panels removed the wind can blow freely through ones mullet.

Tachometer: A gauge in the instrument cluster that displays engine revolutions per minute.

TARDIS: see Time And Relative Dimension In Space

TBI: see Throttle Body Injection

Targa: Italian for “plate”. This term is used to describe a car roof that is partially removable. Usually the portion of the roof directly above the driver and passenger is removable in one piece. Porsche was first to use this term in 1972 even though this type of roof has been around for a long time. Do not confuse with T-top.

TCM: see Transmission Control Module

TCS: see Traction Control System

TDC: see Top Dead Center

TEL: see Tetra Ethyl Lead

Telematics: A generic term used to describe any systems found on the vehicle that can send, receive and store information. Satellite navigation, Bluetooth systems, some entertainment systems.

Tesla Motors: An American auto manufacturer based in Palo Alto, CA. Tesla specializes in all-electric vehicles. Their Model S sedan is selling well enough that it might one day affect the availability of batteries for laptop computers.

Tetra Ethyl Lead: The lead additive that was a common octane booster added to gasoline. TEL was phased out in the early 80’s because it was not compatible with catalytic converts and O2 sensors. Experts also figured it was a bad idea to pump lead out into the air we breathe.

Thermal Efficiency: The difference between the amount of force produced by the engine compared to the amount of heat. Higher thermal efficiency is found with diesel engines because they don’t waste as much energy as heat compared to a gasoline engine.

Throttle Body Injection: An old style fuel injection system that use one or two injectors spraying fuel onto the throttle plates. This system was easily adapted to carbureted engines back when fuel injection was becoming popular.

Thrust Alignment: A wheel alignment procedure where the thrust line is measured and then used as the reference for front toe adjustment. This is used on vehicle with a live rear axle where rear toe and camber are not adjustable in order to correct thrust line faults.

Thrust Angle: The angle measured between the vehicle geometric center line and the direction the rear wheels tend to follow.

Tie Rod: The connecting link in a steering system that connects the knuckle on each side to the rest of the steering linkage. The tie rod is where toe is adjusted.

Tie Rod End: inner and outer. The tie rod in comprised of two ends. The outer connects to the knuckle, and the inner connects to the rest of the linkage. Each end is usually some kind of ball and socket joint. Toe is adjusted by rotating some kind of threaded adjusting mechanism to bring the two ends closer together or push them farther apart.

Timing, Advance: The timing of the spark at the spark plug when the spark must happen much sooner than normal. When the engine is running at high-speed or under heavy load the spark must happen sooner in order to assure the fuel finishes burning in time to push the piston down on the power stroke.

Timing, Base: The timing of the spark at the spark plug without any manipulation from the computer or other mechanisms that might normally alter timing under various conditions.

Timing Belt: A belt connecting the crankshaft to the camshaft(s) used to drive the cams in synchronization with the crankshaft. The timing belt is a serviceable item that must be replaced every 60 to 120k miles. If the belt is not replaced it might break causing major engine damage on some applications. Typically quieter and cheaper than timing chains.

Timing Chain: A chain connecting the crankshaft to the camshaft(s) used to drive the cams in synchronization with the crankshaft. The timing has no replacement interval because they do not break like belts do, but they can stretch when engine mileage gets very high and cause driveability problems. More expensive than timing chains to manufacture but no routine service is required.

Timing Gears: Gears that connect the crankshaft to the camshaft(s) used to drive the the cam(s) in synchronization with the crankshaft. Timing gears are expensive to make but exceptionally strong and never require service.

Timing, Ignition: The timing of the spark jumping the air gap of the spark plug. The spark must hit at just the right time in for the engine to run efficiently. Timing is measured in degrees of crankshaft rotation.

Timing, Initial: The timing of the crankshaft to the camshaft, or the cam shaft to the distributor, or the crankshaft to the distributor. This can be changed based on the way these parts are installed during service or repair. If initial timing is off every other aspect of timing controls will be off. The engine might run but it won’t run well.

Toe: Wheel alignment angle. The inward or outward tilt of the front of the tire when viewed from above or below. Toe angles that are out of specification will cause irregular tire wear, and will cause a pull if one wheel is toed in or toed out more than the other.

Toe-in: A condition where the wheels on a single axle are closer together in the front than they are in the back. Excessive toe-in can cause excessive wear on the outside edges of the tires.

Toe-out: A condition where the wheels on a single axle are closer together in the back than they are in the front. Excessive toe-out can cause excessive wear on the inside edges of the tires.

Toe-Out-On-Turns: A condition that allows a toe out condition on the steering axle when the wheels are turned one way or the other. This is necessary to minimize tire scrub. When turning, the wheel on the inside of the arc must turn at a sharper angle than the wheel on the outside of the arc. A toe-out condition during turning allows this.

Top Dead Center: A term used to describe piston position in the cylinder when it is at the very top of its travel.

Torque: A twisting force. The rotational force produced by an engine.

Torque Converter: A hydrocoupling device used to connect engine output to the input of an automatic transmission. The part of the torque converter that is attached to the engine crankshaft spins against transmission fluid and transmits force to a similar mechanism that is attached to the transmission input.

Torque Steer: A condition common on high performance FWD vehicles that causes the steering wheel to jerk to one side when power is applied. This is caused a by a twist in the drive axles that results in a delay in power application to the wheels.

Torque Multiplication: The process of mechanically trading rotational speed for rotational force. Lower gears in any transmission provide torque multiplication. The car cannot go very fast in a lower gear, but it moves with more force. A small gear driving a larger gear provides toque multiplication.

Torque-to-Yield: A bolt fastener that is made to stretch to help maintain more consistent clamping force. This type of fastener is torqued to a certain specification, then turned a certain number of degrees further regardless of torque applied.

Toyota: A Japanese auto manufacturer founded in 1937 by Kiichiro Toyoda, the son of a textile loom manufacturer. Toyota is the largest auto manufacturer in the world, and is located in it’s own city in Aichi Prefecture of Japan called Toyota City.

TPS: Throttle Position Sensor. A sensor used by various computers to detect the angle of the throttle plate.

Track Bar: see Panhard Rod

Traction Control System: A system that detects wheel slippage and transfers torque away from that wheel to one that has better traction. TCS usually only works at speeds below 30 MPH.

Trailing Arm: A suspension system link usually found on the rear axle of a vehicle that connects to the axle and some point forward of the axle, providing a pivot point of the axle or suspension components to articulate over and through bumps in the road.

Transaxle: A term used to describe a transmission for a front-wheel drive car. This drivetrain configuration integrates the final drive gears and differential gears of the axle into the transmission.

Transducer: A device that converts energy from one form to another. For example a device that can convert oil pressure into a electrical signal.

Transistor: A semiconductor with three layers that can be used as a high-speed electronic switching device.

Transmission Control Module: The computer or ECU that is in charge of electronically controlling transmission function such as when to up shift and down shift. Most modern vehicles integrate the TCM into the PCM so the engine ad transmission computer are the same unit.

Transmission Cooler: A device through which transmission fluid flows in order to cool down before circulating back in the transmission. Most automatic transmissions use a cooler that is integrated into the radiator using engine coolant to cool the ATF. Many A/T systems will use an auxiliary cooler in addition that is a separate unit mounted in front of the radiator using airflow to cool the ATF.

Transmission Filter: A filter usually consisting of a fine mesh screen located in the bottom of the pan on an automatic transmission. Some transmissions may use a spin-on type filter similar to an engine oil filter.

Transverse Mounted Engine: An engine mounting that puts the engine perpendicular to the vehicle center line front to back. This allows a transaxle to be mounted to the engine for a more compact drivetrain. Typically found in front-wheel drive configurations and in many all-wheel drive configurations.

Triton: The nonsensical name given to all engines found in Ford trucks back in the 90’s and early 2000’s. It’s all about marketing as guys like an engine with a tough name. see also, Magnum, Vortec, iForce

Tube Frame: A vehicle frame made from pieces of tubular steel welded together. Usually used in race cars and vehicles with low production quantities.

Tuned Ports: a term to describe intake or exhaust ports that are of a specific and equal length. This is to take advantage of a condition that aids in moving air into and out of the combustion chamber.

Turbo Boost: A operational state wherein the intake manifold is under positive pressure because the turbo charger has spooled and is supplying increased pressure.

Turbo Charger: A forced induction system that uses the flow of exiting exhaust gases from the engine to drive a compressor that acts against the air charge headed into the engine. This causes an increase in volumetric efficiency and allows the engine to use more air and create more power only when needed.

Turbo Lag: The brief delay between the time the engine begins acceleration, and the time the turbo is fully spooled producing boost. This is sensation that can be felt by vehicle occupants in many vehicles.

Turbo Slobber: A condition affecting direct injection diesel engines that is caused by excessive idle time. When the engine idles, temperatures drop so much that water and fuel condense in the exhaust stream and leave a sticky abrasive residue in the exhaust system. This is why idling a diesel is not good. Also known as Combustion Slobber, or Wet Stacking

Turbo Spooling: the action of the turbo charger increasing RPMs to the point that it can provide boost pressure to the intake.

Tweeter: a small speaker that produces high sounds in the treble range. 2. someone who uses Twitter.

TXV: Thermostatic Expansion Valve. see Expansion Valve



UART: see Universal Asynchronous Receive and Transmit

UI: see Unit Injector

U-Bolt: A U shaped bolt that holds a leaf spring to the axle assembly. The U portion of the bolt wraps around the housing, and nuts with washers attach to the U-bolt at the top.

U-Joint: Universal Joint. A flexible joint in a driveshaft that allows a change in angle between the shaft and the drive components while the shaft is rotating.

ULEV: Ultra Low Emissions Vehicle. A tier I emission standard given to qualifying vehicles in the 1990’s by the EPA. Cleaner than LEV, not as clean as SULEV.

ULSD: see Ultra-Low Sulfur Diesel

Ultra-Capacitor: A device that stores electrostatic charge to be used in an electrical or electronic system when a heavy load is placed on the circuit. Typically found in hybrid and electric vehicle designs to aid in rapid acceleration.

Ultra-Low Sulfur Diesel: Diesel fuel containing 15 ppm sulfur or less. Became mandatory for all diesel engines from 2007 on.

Urea: A chemical that contains ammonia that when introduced to exhaust heat will breakdown and cause a reduction of NOx into water, nitrogen, and carbon dioxide. The primary ingredient in diesel exhaust fluid.

Umbrella Seal: A type of valve guide seal shaped like an umbrella. The seal fits over the top of the valve guide and directs oil away from the top of the guide.

Undercarriage: The underneath parts of the chassis.

Undercharge: A state of charge in the A/C where the system does not have enough refrigerant. This results in warm air form the A/C system.

Understeer: a vehicle handling condition where the front wheels lose traction while the rear wheels maintain traction as the cars goes through a turn. The result is the vehicle will not turn in proportion to the amount the driver commands with the steering wheel.

Unibody: A chassis design without a frame where rigidity is obtained by the way the structure is put together. The design will include body panels as sections to add stiffness to the chassis. see also: unitized chassis and monocoque.

Unit Injector: A fuel injector that receives fuel at system pressure but increases the actual injection pressure by being physically acted upon by a camshaft or another device. Used in many older diesel engine designs.

Unitized Chassis: A vehicle chassis design that incorporates structural strengthening members with the body of the vehicle, thus eliminating the frame. see unibody or monocoque

Universal Asynchronous Receive and Transmit: An old network communication protocol used on vehicles during the early years of computer controls. This data bus was primarily used to send serial data to the DLC and scan tool.

Unsprung Weight: The weight of all the components on the vehicle that are not supported by the suspension springs. Tires, wheels, brakes, and axles fall into this category. Unsprung weight contributes to a harsher ride and poor handling.



Valve Cover: The cover that fits on the top of the cylinder head, or engine, that covers the members of the valve train, and leave space which allows them to be splash lubricated with oil as the engine runs.

Valve, Engine: A valve found in the engine that controls the flow in and out of the combustion chamber.

Valve, Exhaust: A valve used to control the the flow of exhaust gasses from the engine cylinder to the exhaust manifold.

Valve Float: A condition where the valve stays open longer than it should, usually the result of more inertia than the valve spring can overcome. May lead to engine damage.

Valve Guide: The steel tube pressed into the cylinder head which houses the valve and allows it to slide open and shut.

Valve, Intake: A valve used to control the flow of fresh air from the manifold to the engine cylinder

Valve Lash: A specific amount of free play between components of the valve train. this looseness allows for expansion and contraction of the valvetrain components. As the engine parts wear some engine require an adjustment of valve lash.

Valve Overlap: A condition that occurs between the end of the exhaust stroke and the beginning of the intake stroke, characterized by both the intake valves and exhaust valves being open at the same time. A high amount of valve overlap leads to greater volumetric efficiency but also affects idle quality.

Valve Seat: A specially hardened steel ring found in the cylinder head around the intake and exhaust ports where the valve closes to seal off the cylinder. The seat must withstand tremendous heat and pressure.

Valve Spring: The spring mounted to the engine valves that closes them automatically when not being acted upon by the cam.

Valvetrain: The mechanisms which drive the valves forcing them open and closed at the correct time.

Vanadium: A chemical element added to steel to increase strength and shock resistance. Used in many tools as well as car parts.

Vapor Management Valve: Ford terminology used to describe the purge control solenoid for the evaporative emissions system. This is the valve that opens to purge fuel vapors from the carbon canister.

Variable Displacement: The ability of an engine to vary its own displacement by shutting down cylinder intake and exhaust valves. If intake valves do not open then no air moves into the cylinder and nothing gets compressed. Subsequently the exhaust valves don’t need to open to allow exhaust out of the cylinder.

Variable Geometry Turbo: A turbocharger that incorporates a mechanism to change the size of the exhaust outlet from the turbo. This is used to allow the turbo to spool more efficiently, and can also be used to enhance back pressure in the exhaust for such functions as engine braking. This device is nearly always computer controlled for greater precision and efficiency. Sometimes called variable nozzle turbo.

Variable Resistor: A resistor that changes resistance based on some kind of input. A type of variable resistor is usually used to give your heater blower different speeds.

Venturi: A device centered in the air stream above the the throttle plate in a carburetor that is designed to create a low pressure area in order to draw fuel from the float bowl of the carburetor. The venturi creates low pressure much the same way an airplane wing does.

VGT: see Variable Geometry Turbo

VIN: Vehicle Identification Number. A 17 digit code that identifies everything about the vehicle.

Viscosity: Internal friction of a fluid, thickness.

Viscous Coupling: A mechanical connection usually found in the drivetrain where the input and output shafts are connected in the coupling though a series of splined clutch discs. When one shaft rotates faster than the other shaft, the resulting friction in the clutches heats the fluid in the mechanism causing everything to expand and a connection is made.

VNT: Variable Nozzle Turbo, see Variable Geometry Turbo

VOC: see Volatile Organic Compound

Volatile Organic Compound: Gaseous emissions that contain carbon that is very reactive with other substances. Photochemical smog forms from a reactive between VOCs and UV radiation from the sun.

Volatility: The degree to which a liquid will vaporize. gasoline is much more volatile than diesel fuel.

Volumetric Efficiency: The difference between how much air can fill a space and how much air actually does fill the space. Higher volumetric efficiency in an engine relates to how well the engine breathes. If the engine breathes well, it will be able to use more air, and subsequently produce more power.

Volt: A unit of voltage. 2. A hybrid Chevy that catches a lot of flack because President Obama said it’s great.

Voltage: Electrical pressure that pushes current through a wire i an electrical circuit. Normal automotive circuits run between 12 and 15 volts.

Voltmeter: A piece of test equipment used to measure voltage, or electromotive force.

Volvo: A Swedish company that manufactures cars, buses, big trucks, heavy equipment, marine drive systems and much more. Not all of these things are manufactured by the same people anymore. The car company is owned by Geely Motors of China. More class 8 trucks with the Volvo name can be found on American roads than the cars of the same name.

Vortec: A nonsensical term used to name any engine found in a Chevy or GMC truck or SUV back in the late 80’s and through the 90’s. Apparently it sounds manly even when used to describe the 2.2L I4 in the S10 pickup, even though it’s the same engine that was in the Cavalier. see also Triton, Magnum, iForce

VMV: see Vapor Management Valve.

VREF: Reference Voltage. A voltage signal sent by the PCM for modification at one of the sensors. The PCM interprets the modified voltage as a sensor reading.

VSA: Vehicle Stability Assist, see Anti-Skid Control

VSS: Vehicle Speed Sensor. A sensor used bay various computers to determine the speed of the vehicle.

VTEC: Valve Timing Electronic Control. A system found on Honda vehicles that can allow intake and/or exhaust valves to follow a different cam profile to change valve lift and duration. Also see iVTEC

Vulcanization: A process of using heat and pressure to treat rubber. Tires are made from vulcanized rubber.

VVT: Variable Valve Timing. A system that can manipulate cam phasing to advance or retard valve timing. 2. Variable Vane Turbo, see Variable Geometry Turbo

VVTi: Variable Valve Timing Intelligence. A term used by Toyota on their engine with VVT.



Wankel: A rotary engine designed by Felix Wankel a German automotive engineer. The Wankel engine has been used most commonly is a few Mazda vehicles.

Warpage: A permanent flexing or bending of a mechanical part that is usually caused by excessive heat stressing.

Washer: A flat O shaped ring that goes under bolt heads and nuts in order to spread out the force applied by the fastener.

Wastegate: A turbo control mechanism that will redirect exhaust gases away from the turbo turbine wheel when boost pressure rises to a certain level. This is computer controlled on all newer turbo systems.

Waste Spark: A distributorless ignition system that uses one coil for two paired cylinders. The coil fires a spark when both cylinders are at TDC. The cylinder that is on the compression stroke will use the spark to ignite the air/fuel mixture, the cylinder that is on the exhaust stroke does not need the spark so it is said to be wasted.

Water Jacket: Coolant passageways in the engine where coolant flows to remove engine heat.

Water Methanol Injection: A technique for cooling combustion chamber temperatures in a diesel engine in order to improve volumetric efficiency. A mixture of water and methanol is injected into the intake air charge and drawn into the cylinders.

Water Pump: The fluid pump found in the engine that is responsible for pumping coolant through the cooling system. The water pump is driven by the crankshaft through an accessory drive belt or a timing belt. Some very modern hybrid cars have electric water pumps.

Watt: A unit for measuring power

Wattage: The measure of total power used per unit of time.

Watt’s Link: A type of panhard rod that uses two horizontal rods that connect at the center, usually at the differential cover. This more effectively controls side to side movement of a live axle assembly.

Watt’s Law: A formula developed by James Watt for calculating total power in an electrical circuit. watts= volts x amps.

Waveform: A voltage or amperage trace usually viewed with an oscilloscope.

Wedge Combustion Chamber: A combustion chamber design that places a single intake valve and a single exhaust valve side by side on the top of a wedge-shaped chamber. This design is mostly outdated but some manufacturers won’t let go of old inefficient traditions.

Wet Compression Test: An engine cylinder compression test where a few drops of oil are added to the cylinder to the spark plug hole. If compression is low, a wet compression test is used to determine if piston rings are worn. If wet compression test numbers are higher than regular test numbers, the piston rings are likely worn.

Wet Sleeve: A replaceable engine cylinder sleeve that when installed into the engine block is in direct contact with coolant in the coolant passageways.

Wet Stacking: A condition affecting direct injection diesel engines that is caused by excessive idle time. When the engine idles, temperatures drop so much that water and fuel condense in the exhaust stream and leave a sticky abrasive residue in the exhaust system. This is why idling a diesel is not good. Also known as Combustion Slobber, or Turbo Slobber

Wet Sump: An engine lubrication system that uses a built-in fluid reservoir at the bottom of the crankcase to store lubricating oil. This is the way most engine lubrication system are configured. see Dry Sump.

Wheatstone Bridge: An arrangement of resistors between an electronic input and output. Used to modify a reference voltage to create some kind of electronic sensor. Commonly used in pressure sensors.

Wheel Alignment: The position of the wheels based on design geometry. 2. The process of adjusting suspension and steering geometry to position the wheels correctly according to design specifications.

Wheel Cylinder: The hydraulic piston assembly used in drum brake systems that takes the hydraulic pressure from the master cylinder and applies it to the brake shoes.

Wheel Offset: The amount that the wheel center-line is found inboard or outboard of the mounting surface. A negative offset puts the center-line inboard and a positive offset puts the center-line outboard, of the wheel mounting surface.

Wheel Seal: A term used to describe the oil seal found on the back side of the hub that contains bearing that must be routinely serviced and repacked with grease.

Wheel Speed Sensor: A sensor mounted on a individual wheel that produces a signal based on the speed of that wheel. These sensors are used for ABS systems, TCS systems, and VSC systems.

Wheelbase: The distance between the centerline of the front and rear wheel when viewed from the side.

Window Regulator: The support structure in the car door that pushes the window up and down.

Witness Mark: A mark made by an object on a another object that shows the two objects making irregular contact.

Woodruff Key: A square key inserted into the key way on a shaft to locate a pulley in the shaft and keep it from slipping around the shaft.

WOT: Wide Open Throttle. What you get when you put the pedal to the metal.

Wrist Pin: A hardened steel rod that attaches the piston to the top of the connecting rod.

WSS: see Wheel Speed Sensor



X-Pipe: A duel exhaust configuration where the two pipes connect in an X formation to aid in scavenging between the two pipes.

Xenon Headlights: A type of headlight bulb that uses high voltage to create an electric arc for the purposes of lighting. Xenon bulbs do not have a filament.

Xylene: An aromatic hydrocarbon used as a solvent. One of the primary ingredients in brake parts cleaner.



Y-Pipe: An exhaust A pipe that connects two exhaust banks from the engine into a single pipe.

Yaw: Rotation around a vertical axis. When a car is in a skid the yaw angle varies from when the car is traveling straight down the road.

Yoke: An input or output member in a drive assembly where a shaft could be attached. U-joints on driveshafts commonly attach to some kind of yoke. 2. The best part of the egg.

YRS: Yaw Rate Sensor: A sensor used by various computers to determine the direction the car is pointed in relation to the direction the car is headed. This sensor can detect when a car turns and how far it turns.



Zahnradfabrik Friedrichshafen: (ZF) A transmission manufacturer based in Germany (as if it wasn’t obvious) that builds transmissions for many different car companies include race car builders.

Zerk Fitting: A fitting used to allow grease to be easily injected into bearings and joints without any disassembly of the of the component being greased. Invented by Oscar U. Zerk in 1929. The name “Zert” as some say, is incorrect and if you pronounce it this way you might get slapped.

ZFM Calibration: Zero Fuel Mass Calibration is a calibration used in diesel injector control modules to allow the computer to compensate for injectors that no longer flow as much fuel as they did when new. Injection volume is critical to diesel engine performance so the PCM watches for a reduction in volume, and changes injector on-time accordingly.

ZF: see Zahnradfabrik Friedrichshafen, but don’t try to pronounce it.

ZEV: Zero Emissions Vehicle. An EPA emissions standard for a car with no emissions. An electric car would have this rating.



4 Door: A vehicle with 4 doors, usually a sedan.

4WD: 4-Wheel Drive. A drivetrain configuration that allows all four wheels to propel the vehicle. 4WD is usually operational part-time ad considered more heavy-duty than all-wheel drive. Also see AWD

4WS: see Four-Wheel Steering


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