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Auto Glossary

Automotive Terms Glossary

Don't know a snap ring from a solenoid? Auto Warranty Broker's glossary of more than 400 automotive terms will help you speak "mechanic" with easy-to-understand definitions and illustrations.

Use this glossary as a quick and easy reference. Need to define a term or learn more about a subject? Just point and click!

Glossary Terms Index

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Automotive Term Definition
All Wheel Drive (AWD) All four wheels are driven by the engine. AWD systems are superior to 4WD because they can be used under any road conditions. AWD systems use a center differential to allow the front and rear wheels to rotate at different speeds. AWD provides better traction than front or rear-wheel drive.
Alloy wheels Wheels usually made of aluminum alloy; installed to improve appearance. Alloy wheels are less prone to corrosion and can be significantly lighter than the equivalent steel wheels.
Alternator A device that converts rotational energy to AC current. Alternators provide energy for the vehicle electrical system. The alternator also recharges the battery.
Anti-roll bar
Sway bar
Stabilizer bar		 A steel rod or tube that connects the right and left suspension members together to resist roll or swaying of the vehicle. An anti-roll bar improves the handling of a vehicle by increasing stability during cornering or evasive maneuvers. Most vehicles have front anti-roll bars. Anti-roll bars at both the front and rear wheels can reduce roll further.
Axle, Live or Rigid A "solid" or "straight" axle that allows the movement of one wheel to affect the opposite wheel. A live axle is inexpensive to manufacture and is useful for heavy duty applications.
Ball Joint Usually refers to the outboard (wheel) end of a CV joint (halfshaft). The ball joint allows the wheel to steer and move with the suspension and still receive power from the engine. The term ball joint can also be used to refer to how suspension components are attached.
Belts Belts are used to drive many engine accessories. Most overhead cam (OHC) engines use cogged (toothed) belts to drive the camshaft(s). Belts drive the power steering pump, water pump, air-conditioning compressors, etc.
Brakes, Antilock (ABS) An acronym for Antilock Braking System. ABS eliminates wheel lockup during braking and loss of steering control on slippery surfaces. Speed sensors monitor each wheel and reduce brake pressure on any wheel rotating significantly slower than the others. ABS systems are 2, 3, or 4-channel systems. 2-channel systems combine 2 wheels, such as the left front and right rear into one channel. The right front and left rear wheel form the other channel. Any wheel lockup causes brake pressure reduction on both wheels of each channel. 3-channel ABS systems combine the rear wheels into one channel. The front wheels have individual channels. The most sophisticated ABS systems use 4-channels, one for each wheel, for maximum control and braking power.
Brakes, Disc A brake that uses a disc shaped rotor and calipers that hold friction pads. The rotor is attached to the wheel hub and spins with it. The calipers are stationary. When the brake pedal is depressed, the calipers press on the side of the side of the rotor. The friction pads slow the rotor as needed. Most vehicles use disc brakes on the front wheels. Disc brakes can shed heat and retain their braking power better than drum brakes.
Brakes, Drum A brake that uses an enclosed rotating drum or "can" and stationary pads (shoes). When the brake pedal is depressed, the brake shoes contact the sides of the "can" and slow the wheel. Drum brakes are usually mounted on rear wheels. Drum brakes are prone to "fade," or heat buildup, which reduces their effectiveness.
Brakes, Calipers Brake pads are mounted to calipers, which "float" next to the brake disc. The caliper ensures that the brake pads exert even pressure on the disc.
Camshaft A machined shaft with lobes that opens and closes engine cylinder valves. The crankshaft drives the camshaft through gears, belts, or chains.
Carburetor A device that mixes fuel and air to provide a combustible mixture. Air blowing over the fuel nozzles (jets) results in an air-fuel mixture burned in the cylinders. Carburetors were common on most vehicles before 1985. Currently, most vehicles use some form of fuel injection instead.
Clutch A mechanism that uses plates coated with a high-friction material to transfer power. Clutches are also used to isolate rotating and non-rotating components. Clutches can allow slip between components to reduce "shock" loads between rotating and stationary components. Manual transmission vehicles use a clutch to transfer power from the gearbox to the wheels. Air conditioning compressors use clutches as well.
Coil Spring A spring composed of hardened steel spiral wound used to isolate a vehicle from the road. Coil springs are preferred over leaf springs for their superior ride and control.
Crankshaft The shaft that converts the linear motion of the pistons into rotation. The crankshaft is connected to the transmission.
Constant Velocity (CV) Joint or Halfshaft A shaft that transmits engine power from the transmission to the wheel. CV joints allow the wheel to steer and follow suspension motion while receiving power. CV joints are used in front-wheel drive, rear-wheel drive, and all-wheel drive vehicles.
Differential A mechanical gearbox or fluid coupling that allows wheels to rotate at different speeds.
Distributor A device that transfers voltage to the spark plug. A rotor in the distributor spins and touches contacts that are connected to spark plug wires. The wires then conduct the voltage to the spark plug.
DOHC Acronym for dual/double overhead cam (see Overhead Cam)
Driveshaft A rotating shaft that transfers power from the transmission to the rear wheels.
Engine, Boxer or Flat A designation for an engine where the cylinders are arranged opposite (180 degrees apart) from each other. Boxer engines are relatively flat compared to inline or "V" engines. Common examples of boxer engines are the Porsche 911 flat-6 and the Subaru flat-4.
Engine, Diesel An internal combustion engine that compresses fuel until it ignites. A gasoline engine, in contrast, uses a spark plug to start combustion. Diesel engines use kerosene as fuel. Diesel engines usually provide better fuel economy than a comparable displacement gasoline engine; at the cost of lower power.
Engine, Inline An engine configuration where all cylinders are in one plane. Most 4-cylinder and some 6-cylinder engines are inline. An inline engine is cheaper to manufacture than a "V" type of engine because the engine block can be a simpler casting.
Engine, V (e.g. V-8):A "V" engine has two banks of cylinders arranged like a "V". "V" engines have an included angle of around 30-90 degrees that separates the individual banks. "V" engines are more compact than comparable inline engines. A V-8 is significantly shorter, and wider, than an inline-8.
Four Wheel Drive (4WD) A part time system that transfers engine power to all four wheels. 4WD systems usually lack a center differential that allows use in dry conditions. 4WD provides superior traction compared with front or rear-wheel drive.
Four Wheel Steering (4WS) A mechanism that allows the rear wheels to steer. The steering angle is usually limited to 2-3 degrees. 4WS improves handling by allowing more stable cornering.
Front Wheel Drive (FWD) The front wheels receive engine power. FWD provides more traction than rear-wheel drive (RWD) in poor road conditions because more weight is over the drive wheels. FWD also allows better use of interior space than RWD because all drivetrain components are concentrated in the front of the car.
Fuel Injection A device (injector) that sprays fuel into air to provide a combustible mixture. Fuel injection provides better metering of fuel and air than carburetors. This results in more power, improved fuel economy, and lower emissions. The simplest systems use single or dual injectors in a central chamber to supply all cylinders. More sophisticated systems use an injector at each cylinder to precisely meter fuel.
Generator A device that converts rotational energy to DC current. Generators were used in older cars to provide electrical energy for the vehicle.
Horsepower (bhp) The power produced by an engine. Net horsepower or bhp (brake horsepower) and Kw (kilowatts) are the standard units. Higher horsepower increases vehicle top speed. Equal displacement (size) engines that rev higher often produce more power than lower revving engines, because more air and fuel is burned in a given time. A typical 3.0L 24V V-6 produces 190 bhp @ 6400 RPM. A lower revving 3.0L 12V V-6 produces 160 bhp @ 5000 RPM. The 24-valve V-6 makes 190 bhp because it can rev higher (and breathe better) than the similar 12-valve V-6.
Independent Suspension A suspension where the motion of one wheel does not affect the opposite wheel. Independent suspension allows a vehicle to provide a more level and stable ride.
Leaf Spring A type of spring made up of several thin, curved, hardened steel plates. The plates are attached at the ends to the underbody. The curved shape of the plates allows them to flex and absorb bumps.
Lights, Driving Auxiliary lights that extend the reach of standard headlights. Driving lights have a narrower beam than headlights.
Lights, Foglights Auxiliary lights that provide a wider beam pattern than standard headlights. Foglights are usually mounted lower than headlights to illuminate below fog and reduce reflected glare.
Lights, Halogen Lights that provide brighter, longer lasting illumination than standard incandescent lights. Halogen bulbs are filled with a gas such as iodine. This gas reduces the gradual evaporation of the tungsten filament and increases its life.
Lights, Projector Beam A special type of headlight that uses a spherical reflector to tightly control the light beam. Projector beams are relatively expensive compared to standard headlights.
Limited Slip Differential (LSD) A differential that reduces speed differences between wheels. An LSD improves traction by preventing a slipping wheel from receiving all the engine power.
Lockup Converter A automatic transmission with a mechanical clutch that bypasses the fluid coupling of the torque converter. A lockup converter is more efficient because there is no wasted energy in the transmission fluid of the torque converter. Most automatic transmissions have a lockup converter for the highest ratio (usually 4th or 5th gear).
MacPherson strut A combined damper (shock absorber) and spring unit. MacPherson struts are used in most front-wheel drive vehicles for compact packaging. MacPherson struts also allow relatively long springs that can increase suspension travel and increase bump absorption capability.
Multi-link suspension A general term for independent suspensions that are controlled with several link arms. These links restrict undesired motion of the suspension. Multi-link suspensions provide better handling and ride control than simpler types. They are also more expensive to manufacture.
Octane A numeric rating of gasoline’s resistance to detonation (premature ignition). The higher the octane number, the less chance of detonation. High octane (above 91) is usually worthwhile only if the manufacturer specifically recommends it. Octane is actually a hydrocarbon(C8H18).
Oil (e.g. 10W-30):Engine oil comes in various ratings: SAE 5W-30, 10W-30, 10W-40, etc. For example, a 10W-30 rated oil will flow like a light SAE 10-weight oil at low temperatures. The "W" signifies that it is a "winter" rated oil. The "30" designation means that at engine operating temperatures, the oil will behave like a heavier SAE 30-weight oil. Low viscosity at colder temperature allows the oil to circulate more quickly and protect vital engine parts. Higher oil viscosity at elevated temperatures prevents direct metal-to-metal contact.
Oil, Synthetic Oil that is not derived from raw petroleum. Synthetic oil has superior engine protection properties compared to conventional mineral oil. Synthetic oil costs 3-5 times more than mineral oil.
Overdrive A transmission ratio below 1:1. For instance, a manual transmission fifth gear ratio could be 0.70:1. Overdrive ratios improve fuel economy by reducing engine RPM at highway speeds.
Overhead Cam (OHC) OHC means overhead cam. The cam is above the cylinder head. SOHC engines have a single cam over the cylinder head. DOHC engines have two cams above the cylinder head. All OHC, SOHC, and DOHC engines are also OHV.
Overhead Valve (OHV) An acronym for overhead valve. This simply means that the intake and exhaust valves are above the cylinder head. OHC means overhead cam. The cam is above the cylinder head. SOHC engines have a single cam over the cylinder head. DOHC engines have two cams above the cylinder head. All OHC, SOHC, and DOHC engines are also OHV.
Oversteer A situation that occurs when the rear wheels contribute to steering the vehicle more in a given direction. This often occurs under hard braking while turning. The rear of the vehicle loses adhesion and starts to rotate in the direction of steering. Oversteer can be used to better place the vehicle coming out of a corner. Usually, oversteer is undesirable because it is difficult to control and can result in a disastrous spin. Most cars are designed not to oversteer under normal conditions.
Pushrod A metal rod that transmits the motion of the camshaft to the valve actuators. Pushrods are used by non-overhead cam engines to open and close valves.
PS Pferdestarke is a measurement of metric horsepower.
Rear Wheel Drive (RWD) The rear wheels receive all the engine power. RWD is preferred over front-wheel drive (FWD) for its superior handling and acceleration capabilities. RWD provides less traction than FWD in poor road conditions because less weight is available over the drive wheels.
RPM Revolutions per minute. RPM indicates how many times the engine crankshaft rotates per minute.
SOHC Acronym for single overhead cam (see Overhead Cam)
Spark Plug The spark plug converts high voltage energy into an arc that passes between its electrodes. The arc causes the gasoline-air mixture in the cylinder to ignite and expand, providing power by pushing down the piston.
Starter A motor powered by the battery that rotates the crankshaft before the engine is started.
Steering, Power Assist provided by the engine to reduce steering effort. Power steering is essential to make large, heavy vehicles manageable. Small vehicles often do not require power steering.
Steering, Rack and Pinion A common steering type. The steering wheel is connected to a pinion gear that meshes with a rack, or linear gear. As the pinion rotates, the rack moves side to side, this moves the steering linkage, causing the wheels to pivot left or right.
Supercharger A device that compresses air before the engine receives it. The denser air allows the engine to produce more power. For automotive applications, a supercharger usually refers to an engine driven air pump.
Tappet A pivoting actuator than opens and closes cylinder valves.
Tires, All Season Tires that provide acceptable traction for winter snow and slush driving conditions, without excessively compromising dry and wet traction.
Tires, Aspect Ratio (e.g. "60-series tires"): Tire aspect ratio is refers to the ratio between the tread (section) width and the sidewall. For example, a 205/50-15 tire would have a sidewall height of 0.50 x 205 or 102.5 mm. Lower aspect ratios(e.g. 40-series) provide superior handling at the cost of increased ride harshness.
Tires, M+S rating Tires especially designed to perform well in mud and snow. M+S tires are usually superior to all-season tires under these conditions. The tradeoff is often higher noise and reduced tread life.
Tires, Ratings (e.g. 300AB):The tire treadwear rating gives an approximate idea of the expected usable life of the tire. A tire rated 300 will probably last 50% longer than a tire rated 200 under identical conditions. Note that since each manufacturer rates tires by its own standards, 300 rated tires from two manufacturers may not provide identical tread life. The traction rating (the first letter) is the manufacturer’s rating of wet traction. "A" is best, "C" is worst. The letter gives some indication of the tire’s resistance to hydroplaning (losing contact with the road at speed). The temperature rating (the second letter) is the manufacturer’s rating of the tire’s resistance to heat build-up. "A" is best, "C" is worst. Heat is the enemy of tires. The cooler the tire temperature, the longer it will last.
Torque A measure of the twisting force. Torque is measured in lb.-ft. (pound-foot) or N-m (Newton-meters). The RPM at which the engine produces maximum torque is important. For instance, if Engine A produces 200 lb.-ft. @ 3000 RPM, and Engine B supplies 200 lb.-ft. @ 5000 RPM, then Engine A will accelerate better at low speeds. Engine B will accelerate better at high speeds.
Torque Converter A fluid coupling used in automatic transmissions to transmit power from the engine to the wheels. The torque converter allows the transmission to be engaged while the vehicle is stopped. The transmission fluid absorbs power and prevents engine stalling.
Torsion Bar A type of spring that twists as it is compressed or stretched. Torsion bar springs are simple and rugged
Traction Control A general term for limiting wheel slip under acceleration. Traction control systems usually apply brakes and reduce throttle when wheel slip is detected.
Turbocharger A type of supercharger that uses a turbine to drive a compressor. The turbine, driven by hot gases in the exhaust manifold spins the compressor. The compressor increases the intake air density, and combined with additional fuel, produces more power.
Twist Beam Axle A semi-independent axle often used on rear suspensions of front-wheel drive vehicles. A horizontal beam connects the two rear wheels together. The beam can twist to reduce the effect of one wheel’s motion on the other wheel. A twist-beam axle is less expensive than a fully independent suspension. It is also more compact.
Understeer Understeer occurs when the front wheels provide less steering than desired in a given direction. Usually the front wheels have lost adhesion and cannot steer effectively. This results in the vehicle "pushing" ahead and responding sluggishly to the steering wheel. Reducing speed can allow the front wheels to regain traction. Most vehicles are designed to exhibit understeer in normal conditions, because it is easier to control than oversteer.
Valves (e.g. 24 valves) Signifies the total intake and exhaust valves in an engine. For example, a 24-valve V-6 would have 4 valves per cylinder: 24/6=4. A 16-valve V-8 would have 2 valves per cylinder: 16/8=2. More valves allow the engine to breathe better at high RPM and produce more power.
Water Pump A pump that circulates coolant within the engine block and cylinder head. The water pump is driven by the engine crankshaft.
Wheel Size (e.g. "15 X 7"): Wheel size is defined by the diameter and width of the wheel. A "15 X 7" wheel has a 15-inch diameter and a 7-inch width.