Appendix A

A Practical Glossary of Automotive Terms

Dictionary of acronyms

If you’ve encountered an acronym in this book and need a quick refresher as to what it refers to, this listing tells you the glossary term it stands for. If you want details, look up that term in the glossary.

ABS: anti-lock braking system

ACC: adaptive cruise control

ADS: Association of Diesel Specialists

BA: brake assist

CNG: compressed natural gas

CV joint: constant velocity joint

CVT: continuously variable transmission

DCT: dual-clutch transmission

EBD: electronic brakeforce distribution

ECM: electronic control module

ECS: emissions control system

ECU: engine control unit

ESC: electronic stability control

EV: electric vehicle

HID: high intensity discharge lamps

ICE: internal combustion engine

ICM: ignition control module

IIHS: Insurance Institute for Highway Safety

MIL: malfunction indicator lights

mph: miles per hour

NGV: natural gas vehicles

NHTSA: National Highway Traffic Safety Administration

NOS: new old stock

OEM: original equipment manufacturer

OHC: overhead cam

PCM: powertrain control module

PCV: positive crankcase ventilation

psi: pounds per square inch

PZEV: partial zero-emission vehicle

R&R: removal and replacement

RSC: rollover stability control

TCS: traction control system

U-joints: universal joints

VIN: vehicle identification number

ZEV: zero-emission vehicle

Words appearing in this font are defined elsewhere in the glossary.

accelerator: The gas pedal.

accessory (or drive) belt: A V-shaped or flat serpentine belt that’s driven by a crankshaft pulley and transmits this drive to various accessories, such as the alternator, air conditioning compressor, fan, power-steering pump, and water pump.

adaptive cruise control (ACC): Transforms cruise control into a system that can be programmed to maintain a safe distance between your car and the vehicle in front of you and to provide protection if a crash seems imminent.

additives: Substances that may be added to gasoline, diesel fuel, coolant, or lubricating oil. Popular additives clean gasoline and diesel fuel injectors, add water pump lubricant and corrosion preventers to coolant, and add viscosity extenders to lubricating oil.

aftermarket: Any product or part not installed on or provided with the vehicle at the time of purchase (stuff you buy after you buy the vehicle, usually from a source other than the automaker).

air bag: An inflatable bladder that pops out of the dash, steering wheel, and/or side panels during a collision to protect the vehicle’s occupants.

air cleaner: A container, called the cold air collector box on modern vehicles, that’s located on or in the air inlet duct to the fuel injection system or carburetor . It contains an air filter, which removes dust and dirt from the air before it enters the engine. (This container also acts as a flame arrester in case of backfire.)

air filter: The element in the air cleaner that removes impurities from the air. Most air filters are disposable, although some aftermarket types can be cleaned and reused.

air inlet duct: The passage through which air travels to the air cleaner and the intake manifold. Also called the air intake duct or air intake hose.

air intake hose: See air inlet duct.

air springs: Rubber bladders filled with air that are computer controlled to cushion the bumps and vibrations of driving. See also suspension system.

air-cooled engine: An engine that uses air instead of water for its cooling system.

alignment: The position of the car wheels relative to the car body. Proper wheel alignment improves handling and performance and reduces tire wear. The front wheels — and on some cars, the rear wheels — have adjustments to allow the alignment to be changed. See also camber, caster, toe-in, toe-out, steering-axis inclination, and turning radius.

Allen wrench: An L-shaped rod designed to remove certain screws and fastenings with hexagonal holes in their heads. These wrenches come in sets of assorted sizes and are sometimes called hex wrenches.

alloy wheels: Ornamental wheels usually made of an aluminum or other metal alloy and typically consisting of spokes radiating out from a central hub to the outer rim.

all-wheel drive: A vehicle on which the drive train delivers power to all the wheels rather than just to the front or rear wheels. Full-time all-wheel drive operates constantly and improves handling even on dry pavement. Selectable all-wheel drive is engaged manually at the driver’s discretion. See also four-wheel drive and traction control.

alternative fuel: A substance other than gasoline or diesel fuel, such as electricity, compressed natural gas (CNG), liquid hydrogen for vehicles with internal combustion engines (ICE), ethanol, and gaseous hydrogen for fuel cells.

alternatively fueled vehicles: Vehicles designed to replace or augment the internal combustion engine (ICE) so as to reduce air pollution and global warming, as well as to reduce demands for fossil fuels. These include hybrids, clean diesels, vehicles with ICE powered by ethanol and hydrogen, natural gas vehicles (NGV) powered by compressed natural gas (CNG), and electric vehicles (EV) powered by batteries recharged from the commercial power grid or by electricity produced onboard by fuel cells.

alternator: Generates electric current that’s stored in the battery and used to start the car and run the electrical equipment. Alternators generate alternating current (AC), which is converted to direct current (DC) before being fed to the battery. Alternators have replaced generators that produced DC but otherwise performed the same functions on older cars.

antifreeze: See coolant.

anti-lock braking system (ABS): Have become increasingly popular because they enhance traction in slippery conditions and allow you to keep steering control of a vehicle, even in a skid. There are two-wheel and four-wheel anti-lock systems.

automatic transmission: A transmission that selects gears automatically, either by means of a hydraulic converter and a system of bands and clutches, or with an electronic transmission controller. Automatic transmissions come in three to seven speeds to provide more control over engine performance and fuel economy. See also continuously variable transmission (CVT), dual-clutch transmissions, and manual transmission.

axle: A solid metal shaft to which the wheels of a vehicle are attached.

backflushing: See flushing the cooling system.

balancing: See wheel balancing.

ball joint: A movable joint found on the steering linkage and suspension system of a vehicle that permits rotating movement in any direction between the parts that are joined. See also boot and constant velocity joints (CV).

bands: Older automatic transmissions rely on hydraulic pressure to change gears by means of a system of friction bands and clutches. These bands can be adjusted externally without taking the transmission apart. Adjusting the bands is part of normal transmission service.

battery: A box filled with a solution of water and acid called electrolyte. The box contains metal plates that store current generated by the alternator and deliver it to the parts of the car that operate electrically. See also ground, negative terminal, positive terminal, and electrical system.

bearings: Antifriction devices that are usually found between two moving parts. For example, the babbit bearings found between the connecting rod and the crankshaft are lubricated and cushioned with oil, and, although the front wheel bearings on front-wheel drive vehicles don’t need servicing, on some vehicles they must be repacked with lube grease at regular intervals. Bearings can be ball- or roller-type.

biocide: A product that kills any fungus or microbes that may have contaminated diesel fuel.

biodiesel: Diesel fuel derived from agricultural and other waste products. It doesn’t produce carcinogenic emissions and can help reduce human dependence on crude oil. See also clean diesel.

bleed: To remove air bubbles from a brake system, a fuel injection system, or a cooling system so that they don’t impede the flow of liquid through that system.

block heaters: Devices that keep the engine warm when a vehicle isn’t used in very cold weather. These are especially important for starting diesel engines at extremely low temperatures.

blow-by: Combustion products that blow past the piston rings during the piston’s power stroke. These products form acid and sludge in the crankcase and, if excessive, can cause smoking from the oil filler hole.

blue books: Listings of the current prices for new and used cars based on age, condition, and optional equipment; published in the Kelly Blue Book, the NADA Used Car Guide (published by the National Automobile Dealers Association), and the Red Book (published by National Market Reports). Blue books are available at bookstores, auto supply stores, banks, loan offices, libraries, insurance companies, and on the Internet at www.kbb.com or www.edmunds.com.

boots: The rubber or plastic covers located at either end of a spark-plug cable to insulate the connections between the cable ends and the spark plug and distributor terminals; always grasp the cable by the boot when removing it. Also the protective cover of ball joints and constant velocity joints that holds the grease. See also grease fitting.

bore: The width or diameter of the cylinder hole. See also stroke.

brake assist (BA): A system that electronically boosts braking power.

brake backing plate: A metal plate, located inside the brake drum, on which the wheel cylinder, brake shoes, and other brake parts are mounted.

brake booster: In a vehicle with power brakes, a brake booster is located between the brake pedal and the master cylinder to increase the force applied to the pistons in the master cylinder. There are two common types: the vacuum booster, which uses engine vacuum and atmospheric pressure; and the hydro-boost unit, which uses hydraulic pressure from your car’s power steering system. Some vehicles with anti-lock braking systems (ABS) have hydraulic pumps to generate pressure for booster operation.

brake discs: Also known as rotors, these are used universally on front braking systems and on some rear braking systems. Brake fluid under pressure pushes pistons in brake calipers, which clamp a set of brake pads against the rotating disc and slow it down, thus slowing down the car. See also brake drums, brake fluid, brake pads, and brake system.

brake drums: Metal drums mounted at the rear wheels on some cars. The brake shoes press against the inner surfaces of the drums to slow or stop the car. See also brake system.

brake fluid: The liquid used in the hydraulic brake system to stop or slow the car. See also brake discs and brake lines.

brake lines: A system of hoses and metal tubes through which the brake fluid flows from the master cylinder to the brakes at each wheel. See also brake system.

brake lining: A high- friction material that’s attached to the brake pad or brake shoe. When the pad is pressed against the disc, or the shoe is pressed against the brake drum, the lining grabs the disc or the inside of the drum, which stops the wheel and thus the car.

brake pads: Friction material on a metal backing plate that, during braking, is clamped around a brake disc by brake caliper pistons to slow down the wheel to which it’s attached. See also brake system and brake fluid.

brake shoes: Curved pieces of metal on which are bonded high-friction brake linings that are forced against the brake drums to slow or stop the car.

brake system: A system that uses hydraulic pressure to enable your car to slow and stop safely. Consists of the master cylinder, brake lines, and disc brakes or drum brakes at each wheel. See also brake discs, brake drums, brake fluid, brake lines, brake lining, brake shoes, parking brake, power brakes, regenerative braking, and wheel cylinder.

bushing: A protective liner that provides a cushion between moving metal parts.

calipers: Devices on disc brakes that hold the brake pads and use hydraulic pressure to force them to squeeze, or grip, the disc to stop or slow the car.

cam: A metal disc with irregularly shaped lobes used in the camshaft to activate the opening of the valves and, in a pre-1975 distributor, to force the points to open.

cam lobes: The bumps on a camshaft that contact and activate cylinder head intake and exhaust valves, either directly or via such devices as camshaft lifters or push rods.

camber: A wheel alignment adjustment of the inward or outward tilt on the top of the wheel when viewed from the front of the car. The correct camber is critical to handling and cuts tire wear.

camshaft: A shaft with cam lobes that causes the valves to open and close. See also cam, overhead camshaft, push rods, and rocker arms.

camshaft sensor: A trigger device found on electronic ignition systems that allows the ECU to synchronize fuel injector operation with the proper cylinder spark plug firing sequence.

carburetor: A device that vaporizes fuel and mixes it with air in proper quantities to suit the varying needs of the engine. Carburetors have been replaced by fuel-injection systems on most vehicles built since 1990.

caster: A wheel alignment adjustment that positions the wheels correctly so that the tires follow naturally in a forward straight line. On a turn, the wheels will tend to straighten out when the steering wheel is released.

catalytic converter: A pollution-control device that acts like an afterburner to consume unburned gas in the tailpipe and to reduce NOx emissions.

cellulosic ethanol: See ethanol.

cetane rating: A method of rating diesel fuel by measuring the time lapse between fuel injection and ignition to determine how easily the oil ignites and how fast it burns. See also octane rating.

charging system: A system that, using an accessory belt driven by the engine, enables the alternator (or generator ) to generate electrical current, which is stored in the battery and delivered to the electrically operated parts of the vehicle.

chassis: The parts of a truck or SUV that are left when the body and fenders are removed.

cherry condition: A popular term for a vehicle that has been kept in — or restored to — perfect condition.

circuit: The path of electrical current through an electrical system.

classic car: A car that’s generally considered to be one of the finest models ever built. Unlike antique cars, classic cars don’t have to be extremely old; for example, Ford Mustangs and Volkswagen Beetles built in the late 1960s have long been referred to as classics. In a few years, these classics will be antiques as well!

clean diesel: A diesel engine that has been modified to run without producing many toxic emissions. Also refers to diesel fuel that burns clean, such as biodiesel and low-sulfur diesel.

clear coat: A finish on modern vehicles that protects the paint and retards rust. See also polymer coating and rubbing compound.

cloud point: The lowest temperature at which diesel fuel tends to thicken and cloud up.

clutch: In a manual transmission, a device that disconnects the engine from the transmission to allow the driver to change gears and then allows the engine and transmission to resume contact and turn together at a new speed. In an automatic transmission, a clutch performs a similar function. See also clutch disk, clutch pedal, engine flywheel, pedal free-play, pressure plate, and throw-out bearing.

clutch disk: In a manual transmission, a spinning plate located at the end of the driveshaft facing the engine flywheel and covered with an asbestos surface. When the clutch is engaged, the clutch disk is forced against the flywheel, causing the engine and the transmission to turn at the same speed.

clutch pedal: A pedal located on the floor of the car to the left of the brake pedal on cars with manual transmission. When the clutch pedal is depressed, it disengages the clutch so the engine and the crankshaft can turn independently of the transmission and the driver can change gears.

coil: See ignition coil.

coil springs: Large metal coils like bed springs that support the weight of a vehicle off the tires, and cushion and absorb the shocks and bumps as a car is driven. Coil springs are usually found near the front wheels, but many cars have them in the rear as well. Often the shock absorbers run up the center of the coil springs. See also suspension system.

cold air collector box: A rectangular box that contains the air filter. It performs the same function as the air cleaner.

combustion: The intense burning of the fuel/air mixture in the combustion chamber.

combustion chamber: The part of the cylinder where the fuel/air mixture is compressed by the piston and ignited by a spark from the spark plug.

common rail fuel injection: A fuel system found in diesel engines. Diesel fuel is pumped at high pressure into a distributor tube called a rail, which delivers fuel to all the fuel injectors.

compressed natural gas (CNG): An alternative fuel designed to replace gasoline as a source of automotive power. See also natural gas vehicles (NGV).

compression gauge: A device used to check the amount of pressure created in a cylinder when the piston is at its highest point and is squeezing the fuel/air mixture into the smallest possible space. A poor compression-gauge reading can indicate the need for repairs such as a valve job or new piston rings.

compression ratio: A measure of the amount of pressure applied to the fuel/air mixture in the combustion chamber. It’s determined by comparing the volume of the combustion chamber when the piston is at its highest point to the volume of the cylinder when the piston is at its lowest point.

connecting rod: The metal rod that connects the piston to the crankshaft and converts the up-and-down motion of the piston into the circular motion of the spinning crankshaft. The phrase “throwing a rod” refers to a broken connecting rod breaking through the side of the engine block .

constant velocity joints (CV): The ball-and-socket fittings that transmit engine power from the transaxle to the wheels. Found mostly at either end of the drive shafts in front-wheel-drive cars and on the drive shafts of some rear-wheel-drive cars with independent rear suspension systems, these joints are specially designed to transmit engine torque while allowing full steering and suspension movement. They allow movement combinations and angles that U-joints are incapable of handling. See also universal joints.

continuously variable transmission (CVT): A computerized transmission with an infinite range (rather than a definite set of physical gears ) that provides optimum performance and fuel economy with less wasted energy from the engine.

control arms: The upper or lower A-shaped suspension components that are mounted on the frame and that support the ball joints and steering knuckles. See also suspension system.

coolant: An ethylene glycol or propylene glycol solution that raises the boiling point and lowers the freezing point of the water in the cooling system, prevents rust and corrosion, and lubricates the water pump. Also called antifreeze.

coolant recovery system: A plastic bottle or metal tank that acts as a reservoir for liquid expelled from the cooling system through the overflow pipe and then returns the liquid to the system when it cools down. This requires a special radiator pressure cap. The system is sometimes called a closed cooling system when it’s part of the original equipment.

cooling system: A system that stores, circulates, and cools a mixture of water and coolant that flows through water jackets in the engine block and cylinder heads and through the radiator in order to keep the engine from overheating as you drive. See also coolant recovery system, fan, pressure cap, thermostat, and water pump.

core charge: “Core” is an acronym for “cash on return.” A sum of money that’s refunded for a rebuildable part that’s exchanged for a rebuilt part of the same type. A common core charge is for an alternator or starter.

core plugs: Metal plugs in the sides of the engine block that can pop out because of excessive pressure from ice formation and can prevent the engine block from cracking. These plugs sometimes develop leaks and should be replaced. Also called freeze plugs.

cotter pin: A locking device shaped like a pin but split up the center. It’s usually inserted in a hole drilled through a nut and bolt and is intended to lock the nut in place so that it can’t unscrew. After insertion, the legs of the cotter pin are bent around the nut to keep it in place.

crankcase: The lower portion of the engine where the crankshaft is located. The oil pan is located at the bottom of the crankcase.

cranking: The act of engaging the starter by turning the key in the ignition switch, which makes the engine turn over. Originally, a hand crank was used to do this, hence the term cranking.

crankshaft: The main rotating shaft in the engine. The connecting rods transmit power from the pistons to the crankshaft, which in turn transmits power to the transmission, then to the driveshaft, and eventually to the drive wheels.

crankshaft position sensor: A trigger device that tells the powertrain control module the position of the crankshaft. This input allows for proper timing of ignition and fuel injection, among other things.

crankshaft pulley: A grooved wheel attached to the front end of the crankshaft. The pulley is connected by accessory belts to the fan, alternator, power steering pump, water pump, air conditioning compressor, and other devices so that the rotating crankshaft can drive these other parts as well. The crankshaft pulley usually has timing marks located on it, and these are necessary for checking and adjusting timing with a timing light on older vehicles. Also called a harmonic balance wheel.

creeper: A platform on wheels that allows you to move around easily while lying on your back when you work under your vehicle.

cross-shaft lug wrench: See lug wrench.

cruise control: An optional feature that keeps your car cruising at a preset speed unless overridden by the brake pedal.

cylinder: A hollow, tube-shaped pipe in the engine block. The piston rides up and down in the cylinder to compress the fuel/air mixture that drives the engine.

cylinder block: See engine block.

cylinder head: The part of the engine above the engine block that contains the combustion chambers and the valves. The spark plugs screw into the top or side of the cylinder head. On most cars, a valve cover, camshaft cover, or rocker-arm cover is located on top of the cylinder head.

cylinder sequence: The order in which the cylinders are located on a particular vehicle. It’s necessary to locate the #1 cylinder to check and adjust timing with a timing light. The #1 cylinder may be at the front of the engine on a United States-made straight 4- or 6-cylinder engine or at the rear of the engine on a foreign-made car. See also firing order.

diesel engine: An engine that burns diesel fuel instead of gasoline. The diesel fuel is injected directly into the combustion chamber, or a pre-combustion chamber on some vehicles, where it’s ignited by the heat caused by intense compression rather than by a spark from a spark plug.

diesel fuel: Fuel for cars with diesel engines. It’s similar to home heating oil, kerosene, and jet fuel. Also known as diesel oil. See also biodiesel, clean diesel, and cetane rating.

dieseling: An engine on older, carburated vehicles that continues to run after the ignition switch has been turned off is said to be dieseling.

differential: A “box” of gears, situated in rear-wheel drive cars between the rear wheels, that turns the power of the rotating driveshaft at right angles to drive the rear axles and rear wheels. In front-wheel drive cars, the differential is located in the transaxle. The differential also allows each of the drive wheels to turn at a different speed when cornering.

dipstick: A metal stick that’s inserted into a reservoir to check the level of the fluid in the reservoir by means of markings on the stick. The most common dipsticks check the levels of engine oil, transmission fluid, and power-steering fluid.

disc brakes: Brakes that have calipers with high-friction brake pads, which grab a brake disc (sometimes called a rotor) attached to the wheel and force it to stop turning, thus stopping the car. Older cars have disc brakes on the front wheels and drum brakes on the rear wheels. Many other cars have disc brakes on the front and rear wheels.

displacement: The volume of the inside of the cylinders. The amount of fuel and air that the cylinders can hold before compression takes place.

distributor: The part of the ignition system that distributes the proper amount of electrical voltage to each spark plug in the correct sequence. This task is now performed electronically on distributorless ignition systems. See also engine control unit (ECU) and electronic ignition system.

distributor cap: A cap that covers the distributor. It has an outlet for each spark plug wire, plus an outlet where the wire from the ignition coil enters the cap to conduct high-voltage electrical current to the rotor. The cap keeps dirt and moisture from getting into the distributor.

distributorless ignition system: An electronic ignition system that doesn’t contain a distributor and contains multiple ignition coils.

downshifting: Shifting manually to a lower gear to accelerate, provide more power to climb a steep hill, or use engine drag to slow down on a grade.

drive train: The path of power from the engine to the drive wheels. Consists of the clutch, transmission, driveshaft, differential, and the axle on which the drive wheels are situated. On front-wheel drive vehicles, the transmission and differential are combined into one unit called a transaxle, which connects directly to the drive wheels.

drive wheels: The set of wheels that are connected to the driveshaft or transaxle and actually drive the vehicle forward and backward while the other set of wheels may simply turn in response to the car’s motion. Vehicles are now identified as having front-wheel drive, rear-wheel drive, four-wheel drive, or all-wheel drive.

driveshaft: In rear-wheel drive cars, the spinning metal shaft that transmits power from the transmission to the differential, the rear axle, and the rear wheels. In front-wheel drive cars, two shorter driveshafts transmit power from the transaxle to the front wheels.

drum brakes: Brakes that use hydraulic pressure to force curved brake shoes against the inner walls of a hollow metal drum attached to each wheel. See also brake system, disc brakes, and anti-lock braking system (ABS).

dual-clutch transmissions (DCT): Transmissions that offer the driver the choice of shifting gears manually or letting the vehicle do it automatically.

electric vehicle (EV): An alternatively powered vehicle designed to use an electric motor as an environmental improvement over the internal combustion engine.

electrical system: A system that generates, stores, and distributes the electrical current required to start and run your vehicle and such electrically operated equipment as the radio, headlights, power seats, windows, air conditioner blower, and engine control unit (ECU). See also charging system, ignition system, and starting system.

electrodes: Metal rods attached to the center and side of the spark plugs to conduct current and create a gap across which the spark must jump.

electrolyte: The mixture of sulfuric acid and water that’s found in the battery.

electronic brakeforce distribution (EBD): A system that distributes brake power proportionately among the four wheels.

electronic control module (ECM): A generic term for an on-board computer that is responsible for controlling the operation of one or more electronic systems. The earliest example replaced the points in mechanical distributors in the mid-1970s.

electronic ignition system: A computer-controlled ignition system that transmits electrical current to the spark plugs by electronic means, eliminating the need for gap ping and replacing distributor parts and frequent tune-ups. Modern distributorless ignitions have ignition control modules (ICM) or are controlled by the ECU. Older electronic ignition systems with distributors controlled by an electronic control module (ECM) are still on the road but are disappearing fast.

electronic sensing devices: See sensors.

electronic stability control (ESC): A system designed to help prevent a vehicle from skidding, spinning, or rolling over and to help return it to its intended path when it goes out of control. Using the sensors and computers that enable ABS and TCS, it monitors how the vehicle is responding to the steering wheel and helps you keep control of your vehicle by activating individual brakes and reducing power.

emergency brake: See parking brake.

emissions control system (ECS): Parts on a vehicle that reduce or remove harmful substances from the exhaust gases and recycle unburned fuel vapors before they get into the air and contribute to pollution and global warming. These parts include the PCV valve, various sensors, a catalytic converter, and other components. See also exhaust system.

engine: The part that produces power to drive a vehicle. It’s usually fueled by gasoline or diesel fuel but may be powered by alternative fuels .

engine block: The cast iron, aluminum, or ceramic block in which the cylinders and the crankshaft are located. Also called the cylinder block.

engine control unit (ECU): The most powerful computer onboard a modern vehicle, also called a powertrain control module (PCM). Controls most engine functions including spark and valve timing, emissions controls, air/fuel mixture, fuel delivery, and even the cooling fan . The ECU also processes signals from all the various engine, emissions, and related sensors. See also electronic sensing devices, onboard computers, and transmission controller.

engine flywheel: A spinning plate located at the end of the crankshaft on vehicles with manual transmissions that engages the clutch disk, causing the engine and the transmission to turn at the same rate of speed. Also helps to dampen engine vibration. The starter turns the flywheel in order to start the engine. See also clutch.

engine management computer: See engine control unit (ECU).

EPA estimates: Estimates of the average amount of fuel consumed in city and highway driving by a particular vehicle, based on tests administered by the Environmental Protection Agency (EPA). These estimates should be used for comparison only because they vary with the driver, the load, and road conditions.

ethanol: An alcohol fuel distilled from plant materials such as corn and sugar. Cellulosic ethanol based on non-food agricultural products such as switch-grass and waste products offers the potential of fueling vehicles without negatively affecting the world’s food supply. Fuels made from a blend of gasoline and alcohol fuels like ethanol or methanol are also known as gasohol.

exhaust gases: The burned residue of the fuel/air mixture that must be processed by the catalytic converter and expelled from the vehicle via the exhaust system.

exhaust manifold: A set of pipes that carry exhaust gases from the engine to the exhaust system and out of the vehicle through the tailpipe. See also intake manifold.

exhaust port: The opening in the cylinder head that enables the exhaust valve to allow the fuel/air mixture out of the combustion chamber.

exhaust system: The system that conducts exhaust gases from the exhaust manifold away from the passenger cabin to the tailpipe and into the air. Along the way, devices in the emissions control system (ECS) burn off or remove harmful substances, and a muffler (and resonators in some cases) controls the noise of the escaping gases. See also catalytic converter, PCV valve, and resonator.

exhaust valve: The valve that opens to allow the exhaust gases to pass from the combustion chamber to the exhaust manifold.

fan: Electrically driven and mounted in front of the radiator — or, in older vehicles, driven by an accessory belt and situated between the radiator and the engine — the fan draws air through the radiator to cool the liquid in the cooling system when the car is standing still or operating at low speeds, or when the air conditioner is running. Electrically driven fans are controlled by a thermal sensor in the cooling system.

fan belt: On older vehicles, a single flexible rubber belt that connects the fan, the water pump, and the alternator on some older vehicles. The operation of the engine turns the fan, which turns the belt, which drives the alternator, enabling it to generate electric current. See also accessory belt.

feeler gauge: A device for measuring the distance, or gap, between two surfaces. Use a wire or taper feeler gauge to gap spark plugs.

firewall: The insulated partition that runs from the windshield down between the interior of the vehicle and the engine compartment. Protects the driver and passengers from engine fires, noise, and fumes.

firing order: The sequence in which the cylinders fire on a particular engine to distribute the shock of combustion evenly and to reduce engine vibrations. This shouldn’t be confused with cylinder sequence, which refers to the location of the #1 cylinder on a specific vehicle and where the other cylinders are located in relation to #1.

flash point: The temperature at which diesel fuel ignites.

flat rate manual: A listing of almost every repair and maintenance job that can be done on a particular vehicle with the average time required for a technician to complete it. Used by service facilities to estimate labor charges. Unscrupulous shops require their mechanics to “beat the book” yet charge their customers for the full time suggested by the flat rate manual.

flex-fuel vehicles: Vehicles that can operate on more than one type of fuel. Also called dual-fuel or multi-fuel vehicles.

flushing the cooling system: Circulating water through the cooling system to remove old liquid and clean the system of rust and dirt. Backflushing means circulating the water from the engine to the radiator (reversing the normal direction of flow) in order to clean the system more efficiently. Flushing is easy to do but requires recycling of the old coolant, which is toxic to animals and small children.

fossil fuels: Fuels derived from petroleum, such as gasoline and diesel fuel. Because fossil fuels are in dwindling supply and are a major cause of global warming , vehicles that run on it now are being replaced by alternatively fueled vehicles.

four-stroke power cycle: Refers to the four movements of the piston — down and up, down and up — that draw the fuel/air mixture into the combustion chamber (intake stroke ), compress the mixture (compression stroke), transmit the power created by the combustion to the crankshaft (power stroke), and expel the exhaust gases from the cylinder (exhaust stroke).

four-wheel drive: Allows a driver to adjust a vehicle to operate in difficult terrain; how this is accomplished differs from one model to another. Four-wheel drive should be used only when needed because it doesn’t work efficiently under normal road conditions. See also all-wheel drive.

freeze plugs: See core plugs.

friction: The rubbing of two moving parts against each other. Friction creates heat and wears down moving parts. The lubrication system uses oil to reduce friction and to increase the life of your vehicle. Friction is used between brake pads and brake discs and between brake shoes and brake drums to slow down and stop your car.

front-end alignment: See alignment.

front-wheel drive: A vehicle that’s “pulled” by its front wheels rather than “pushed” by its rear wheels has front-wheel drive. This arrangement eliminates the long driveshaft and the center floor hump found on cars with rear-wheel drive. See also transverse engine, transaxle, and constant velocity joints.

fuel/air mixture: A vaporized, mist-like combination of fuel and air that’s compressed in the cylinders and ignited to produce the power that drives the engine and the vehicle.

fuel cell: A power plant that creates electrical current from hydrogen and oxygen that’s passed over a catalyst, usually a microscopically thin sheet of platinum. The electrical current then is fed directly to the vehicle’s electric motor for propulsion. See also alternatively fueled vehicles.

fuel filter: A device that removes impurities from the fuel before it gets to the fuel injection system. In fuel-injected cars, the filter is found either in the fuel line under the car, or mounted on the firewall.

fuel gauge: A dashboard device that indicates the amount of fuel in the fuel tank.

fuel injection: A fuel system without a carburetor that employs an electronic fuel management system to deliver a specific amount of fuel to each combustion chamber in response to changes in engine speed and driving conditions. See also engine control unit (ECU) and fuel injectors.

fuel injection pump: Found mostly on diesel engines, it sends fuel under high pressure to the fuel injector nozzles. See also fuel rail assembly and fuel transfer pump.

fuel injector: A device that receives fuel at a constant pressure and is controlled by the ECU, which adjusts the amount of fuel sprayed into each combustion chamber by varying the length of time it holds the injector open.

fuel lines: The hoses or pipes through which the fuel passes from the fuel tank to the fuel injectors.

fuel pressure regulator: A spring-loaded diaphragm that maintains proper fuel pressure and meters unused fuel back to the fuel tank.

fuel pump: A pump that draws the fuel from the fuel tank and sends it through the fuel lines to the fuel injectors.

fuel rail assembly: A pipe in a fuel injection system that supplies fuel to the set of fuel injectors connected to it.

fuel supply pump: See fuel transfer pump.

fuel system: A system that stores, cleans, and delivers the fuel to the engine in proper quantities to meet the varying needs that arise as you drive. Consists of the fuel tank, fuel lines, fuel pump, fuel filter, and fuel injectors (or the carburetor on older vehicles without fuel injection).

fuel tank: The storage compartment, under the trunk in most cars, that holds the fuel for the vehicle.

fuel transfer pump: One of a series of mini-pumps on diesel engines, each of which is responsible for delivering fuel from the fuel injection pump to one of the fuel injector nozzles at a pressure of more then 1,000 psi (pounds per square inch). Also found on gasoline engines.

fuses: Fuses protect the electrical components and wiring on your vehicle the same way they do in your home. They’re located in a fuse box (or boxes) that usually are found under or near the dashboard or under the hood. Your owner’s manual can help you locate yours.

gap: The space between the spark plug electrodes. Adjusting this space is called “gapping.” See also feeler gauge.

gapper: See feeler gauge.

gas gauge: See fuel gauge.

gas tank: See fuel tank.

gasket: A rubber, cork, paper, or metal plate that’s inserted between two parts to prevent leakage of gases, fluids, or compression.

gasohol: See ethanol.

gear ratio: The speed of the engine compared with the output speed of the transmission and/or the differential in a given gear.

gear selector: A gearshift for vehicles with automatic transmissions. It can be located on the side of the steering column, in a console, on the dashboard, or on the floor between the front seats.

gears: Devices that enable the transmission to move a vehicle forward and backwards at a variety of speeds. See also automatic transmission, manual transmission, gear ratio, gear selector, and gearshift.

gearshift: The stick often located between the front seats on vehicles with manual transmissions that the driver uses to select and change transmission gears. See also gear selector and stick shift.

generator: See alternator.

global warming: An environmental crisis brought on by the unrestricted use of fossil fuels, carbon emissions, and a variety of other manmade conditions, which results in the heating of the Earth’s atmosphere and oceans, weather changes, melting of glaciers, decline of species, and other natural disasters. See also alternatively fueled vehicles.

glow plug: An electrical element located in the combustion chamber of a diesel engine that helps to heat up the air in the chamber so that the diesel fuel is ignited more quickly.

governor: On diesel engines, it controls the exact amount of fuel that’s sent to the fuel injector nozzles and makes sure that the engine doesn’t go so fast that it damages itself with excessive heat and pressure.

grease fitting: A device that seals in grease to cushion two moving parts, allowing them to move freely and preventing them from wearing each other away. See also ball joint, steering knuckles, and tie rods.

grease seal: A circular, metal-backed, rubber device, that keeps grease from leaking out and protects wheel bearings and similar parts from dust and water.

ground: An object that makes an electrical connection with the earth, to safely complete an electrical circuit. For example, one terminal of the battery is wired to the metal frame of the vehicle to utilize the frame as a path for returning electric current to the battery and thus completing the electrical circuit. All vehicles made in the U.S. are negative ground because the negative terminal is wired to the frame. In some countries, this is called negative earth.

guarantee: A promise by the manufacturer to fix or replace a specific part if it doesn’t last for a specific time period or distance. See also warranty.

harmonic balance wheel: See crankshaft pulley.

head gasket: The seal between the cylinder head and the engine block. This gasket keeps the coolant out of the cylinders and free from contamination by exhaust gases. A “blown” head gasket causes a serious loss of compression.

headliner: Fabric or vinyl upholstery on the interior of the roof of a vehicle.

heater core: A device that heats the passenger compartment. Hot coolant and water circulate through it from the engine and heat air that’s then blown by an interior fan into the vehicle

hex wrench: See Allen wrench.

high intensity discharge lamps (HID): Headlamps filled with halogen or xenon gas that are brighter and use less power than the sealed beam units they’ve replaced.

horsepower: The energy required to lift 550 pounds one foot in one second — or 33,000 foot-pounds per minute.

hose clamps: Adjustable metal rings placed around a hose where it connects to another part to prevent leaks and to keep the hose in place.

hubcap: See wheel cover and alloy wheels.

hybrid: An alternatively fueled vehicle that combines a small internal combustion engine and an electric motor to get maximum power with minimum emissions and maximum fuel economy.

hydraulic: A system that uses fluids under pressure to transmit force or power. Hydraulic devices on a vehicle may include automatic transmission, power steering, and brake systems.

hydrometer: A device to determine the specific gravity of a liquid. It’s used to test battery electrolyte and the percentage of coolant in the cooling system.

idiot lights: Popular term for the dashboard indicators that light up only when your car is already in trouble from lack of oil, overheating, and so on (as opposed to gauges, which indicate levels of oil and engine temperatures, thus enabling the driver to prevent breakdowns and damage). See also malfunction indicator lights (MIL).

idling: The engine speed when a vehicle isn’t moving.

ignition coil: The part of the ignition system that receives a small amount of electrical voltage from the battery, amplifies it into a big jolt of voltage, and sends it to the spark plugs via the distributor (if the vehicle has one). On electronic distributorless ignition systems, each spark plug may use its own coil.

ignition control module (ICM): A computer on an electronic system that receives data from sensors and controls the firing of the spark plugs, sometimes controlled by the engine control unit (ECU).

ignition switch: The means by which you activate a vehicle’s electrical circuits and start the engine. On many vehicles, it’s a slot in which you insert the key to the car. When the key is turned to Off, the electrical circuits are disconnected from the battery. Other vehicles may have an ignition button to push instead. See also keyless ignition and keyless entry.

ignition system: A system that provides the high-voltage electric current used to ignite the fuel/air mixture in the combustion chambers of the cylinders. Its parts include the ignition coil , which amplifies the voltage it gets from the battery and sends it to the distributor, which directs the current to each spark plug at the proper time. In cars with distributorless ignitions, the engine control unit (ECU) directs low-voltage current to the spark plug coils and then to the spark plugs .

ignition timing: The timing of the spark plug spark in the combustion chamber during the piston ’s compression stroke . This timing is preset by the auto manufacturer and rarely needs to be adjusted in vehicles with electronic ignition systems. In vehicles with engine control modules or distributorless ignitions, no manual adjustment can be made.

injector driver: A transistor that is located in, and controlled by, the ECU. It controls how much fuel to spray into each cylinder to mix with the air in order to get the optimum explosion to drive the piston.

injector pulse width: The amount of time that the engine control unit (ECU) maintains the electrical circuit to a fuel injector. Using information it receives from a variety of sensors, the ECU changes the pulse width and controls the fuel/air mixture.

inlet valve: See intake valve.

in-line engine: An engine in which the cylinders are set in a single row with the crankshaft running along the bottom. Also called a straight engine. See also V-type engine.

intake manifold: This chamber is found near the top of the engine; it routes the air needed for combustion to the cylinders. See also exhaust manifold.

intake port: The opening in the cylinder head containing the intake valve , and through which the air and fuel passes into the combustion chamber. See also four-stroke power cycle.

intake valve: A valve that opens to allow the fuel/air mixture to enter the combustion chamber. Also called the inlet valve.

integral equipment: Any device or system that’s designed for, and installed in, a vehicle by the manufacturer rather than added to a finished vehicle at a later date.

internal combustion engine (ICE): An engine that works on power released by vaporized fuel and air burning inside the engine itself, rather than on an outside source of combustion as, for example, a steam engine does.

jack: A device for lifting all or part of a vehicle off the ground to facilitate repairs. The most popular jacks are tripod, scissors, and hydraulic jacks.

jack stand: A safety device that keeps the vehicle from falling to the ground if the jack is removed or faulty. Most jobs require two jack stands for safety.

journal: The area on the crankshaft that fits into the bearings in the engine block and the lower portion of the connecting rod(s). A layer of oil and metal bearings cushions the movement of the journal to prevent premature wear.

jumper cables: Cables used to jump a start by conducting current from one battery to another, allowing a vehicle whose battery has run down to start and begin to generate its own power. Jump-starting can injure onboard computers on some vehicles. Before using jumper cables, consult your owner’s manual for instructions. See also negative terminal and positive terminal.

keyless entry: A feature that allows you to open a vehicle’s door without a key because the vehicle recognizes a chip in a remote device. Some keyless entry systems require you to click the remote, whereas others can sense its presence without “seeing” or “hearing” it. See also keyless ignition.

keyless ignition: A feature that allows you to start and run a vehicle with no need to place a key in the ignition switch. This feature often is combined with keyless entry.

knocking: A sound that occurs in the cylinders when the fuel/air mixture is ignited too soon and the subsequent explosion hits the piston as it travels up the cylinder on the compression stroke. Also called pinging, detonation, or pre-ignition. Usually, it’s due to faulty timing, gas with a low octane rating, or a build-up of carbon in the cylinders. Knocking sounds like marbles rattling in a can and can be heard best when accelerating up hills. The term is also used to describe the sound a worn-out bearing or piston pin makes. See also four-stroke power cycle.

leaf springs: A series of flexible steel plates, placed one on top of the other, that carry the weight of the vehicle and bend to absorb the bumps and shocks of driving. They’re most often used in the rear suspensions of trucks and some sport-utility vehicles. See also suspension system.

lubrication system: A system that stores, cleans, cools, and recirculates oil through the engine to lubricate and cool its moving parts. The system components are the oil pan, oil pump, oil filter, and dashboard oil gauge or warning light. You can check the level of oil in the system with the oil dipstick.

lug nuts: The nuts that hold the wheel onto a vehicle. You remove them with a lug wrench in order to change a tire. Some vehicles use lug bolts instead.

lug wrench: A wrench used during tire changes to remove the lug nuts that hold the wheel onto the car. The cross-shaft type of wrench provides the best leverage. Carry one in your trunk.

malfunction indicator lights (MIL): Dashboard alerts that are activated by various electronic control modules which check many automotive systems and alert drivers to conditions that need checking and possible adjustment or repair. Also known as warning lights or “Check Engine” or malfunction indicator lamps.

manifold: See exhaust manifold and intake manifold.

manual transmission: A transmission system in which gears are selected by the driver by means of a hand-operated gearshift and a foot-operated clutch . Also called a standard transmission. See also automatic transmission and gear selector.

master cylinder: A device that stores brake fluid and hydraulically forces it through the brake lines to the brakes when you step on the brake pedal. Hydraulic clutches have master cylinders, too.

mechanic’s lien: Recourse available to repair facilities in some states by which they can confiscate and sell your vehicle to compensate themselves if you don’t pay your bill.

misfiring: The failure of the fuel/air mixture in one or more cylinders to undergo combustion while the vehicle is running. Misfiring can be due to poor compression caused by worn or improperly adjusted valves, worn piston rings, or a faulty head gasket. Or it can be caused by poor ignition due to worn, dirty, or improperly gapped spark plugs, poor fuel delivery, or faulty ignition wiring. Misfiring can be detected by placing a stiff piece of paper at the end of the tailpipe and listening for an irregular puffing sound.

motor mounts: The brackets that hold the engine and transmission to the frame of the car and have rubber or polyurethane elements that cushion vibrations.

muffler: A device for controlling the noise of the exhaust gases before they’re released into the air through the tailpipe. Mufflers also help control exhaust gas pressure. Some innovative systems use specially designed piping, sometimes combined with electronics, to cancel out loud exhaust tones and to muffle the noise without an actual muffler, thus allowing the exhaust to flow more freely, which improves engine performance and fuel economy. See also resonator.

natural gas vehicles (NGV): Vehicles powered by compressed natural gas (CNG).

negative ground: See ground.

negative terminal: The battery terminal that conducts electric current back to the battery. The negative terminal usually has either “NEG” or “–” on it.

non-electronic ignition system: An ignition system found on older vehicles with carburetors that needed frequent tune-ups involving the gapping and replacing of distributor parts.

NOS (new old stock): New parts made in the past for out-of-production vehicles that are used in their restoration. See also OEM (original equipment manufacturer).

NOx emissions: A familiar term for the toxic oxides of nitrogen that pollute the air if they aren’t reduced or removed from exhaust emissions.

octane rating: A method of rating gasoline by measuring its ability to resist knocking in internal combustion engines. Engines with higher compression ratios require higher-octane gasoline. See also cetane rating.

odometer: A dashboard device for measuring and indicating the number of miles a vehicle has traveled. Some vehicles also have a trip odometer that can be set to zero in order to register the mileage on a particular trip.

OEM (original equipment manufacturer): Parts supplied by the original manufacturer of a particular vehicle. See also NOS (new old stock), rebuild, replacement parts, and remanufactured.

oil: A substance that lubricates and cools the moving parts of the engine and reduces the formation of rust and corrosion. Oil comes in varying weights suitable for efficient operation in cold and hot weather and for engines in varying states of wear. See also viscosity.

oil drain plug: The plug that secures the drain hole in the oil pan. In many (but not all) vehicles, an oil plug gasket lies between the plug and the hole and should be replaced if leakage occurs. In some vehicles, there’s no gasket because the metal-to-metal connection between the drain plug and the oil pan is tapered and leak-free.

oil filler hole: A hole at the top of the engine through which new oil can be added after the filler hole cover is removed.

oil filter: A can-like device that screws onto the outside of the crankcase and cleans the oil as it circulates through the lubrication system. Oil filters should be replaced as part of every oil change.

oil pan: The chamber at the bottom of the crankcase that stores oil. The oil drain plug at the bottom of the oil pan can be removed to allow old oil to flow out of the car during an oil change.

oil pressure gauge: A dashboard device that indicates the oil pressure as the oil is pumped through the engine. If this gauge shows a sharp drop, reads “Low,” or lights up, stop the car immediately and find the reason for your loss of oil pressure before driving any farther. Without oil pressure, you can burn out your engine in a very short time. A low indication doesn’t necessarily mean that you’re low or out of oil in your oil pan; among other things, it could mean that the oil pump is defective or has failed. See also malfunction indicator light (MIL).

oil pump: A small pump located in the crankcase that circulates the oil from the oil pan to the moving parts of the engine.

onboard computer: One of many computers that may control ignition systems, fuel systems, heating, ABS, airbag deployment, electronic stability control, traction control, rollover stability control (RSC), seat belt pre-tensioning, and other systems. See also ECU (engine control unit), electronic sensing devices, sensors, system management computers.

optional equipment: Any equipment or feature of a new vehicle that isn’t included in the basic price and is provided only if the purchaser requests it. Beware of new car deals that force you to buy a vehicle equipped with options you don’t need.

original condition: Refers to an older vehicle that has all its original paint and equipment and hasn’t been restored or modified.

overdrive: A special gear that allows the rear wheels to turn faster at the same engine rpm. Overdrive lowers fuel consumption during sustained high-speed driving on highways.

overhaul: See rebuild.

overhead cam (OHC): A camshaft located above the cylinder head. Overhead camshafts eliminate the need for push rods to activate the valves. Double overhead cam (DOHC) engines have two overhead camshafts: One operates the intake valves, and the other operates the exhaust valves.

owner’s manual: A handbook provided by the car manufacturer to give the owner basic instructions for operating the various devices on a vehicle. Many owner’s manuals contain specifications for items associated with maintenance, but very few offer instructions for doing it yourself. See also service manual.

ozone checking: Cracks or hard spots usually found on the sidewalls of tires. Caused by the action of the ozone in the air on the rubber, this condition is normal but could be dangerous on tires that are more than 40,000 miles old or that have been exposed to ozone for a long time.

parking brake: An auxiliary brake, usually attached to a rear wheel or to the transmission, that keeps the vehicle from moving accidentally. Also called an emergency brake.

partial zero-emission vehicles (PZEV): Vehicles with internal combustion engines that are so clean-running that they almost meet California’s zero-emission standards. See also zero-emission vehicles.

passing gear: A gear on automatic transmissions that shifts a vehicle into a lower gear for a short burst of extra power to pass other vehicles on the highway. This gear is engaged by sharply depressing the gas pedal. When the pedal is released, the car returns to a normal driving gear.

PCV valve: Part of the positive crankcase ventilation system, which routes crankcase blow-by to the intake manifold and back to the engine where it’s reburned in the cylinders as part of the fuel/air mixture. This action cuts emission pollution and increases fuel economy because unburned fuel in the blow-by is consumed the second time around. It also keeps the blow-by and water vapor from fouling the oil in the crankcase, thus reducing the formation of engine sludge.

pedal free-play: The distance the clutch pedal can be depressed before it begins to disengage the clutch. About 3/4 to 1 inch of pedal free-play is normally required to assure that the clutch will be fully engaged when not in use. Without pedal free-play, the throw-out bearing and/or the clutch would wear out.

Phillips screwdriver: A screwdriver with a pointed tip that’s shaped to fit the crossed slots in the heads of Phillips screws.

pinging: See knocking.

piston: A cylindrical part, closed at the top, that moves up and down inside the cylinder to compress the fuel/air mixture and drive the engine by means of a connecting rod that’s attached to the piston at one end and to the crankshaft at the other. See also journal and piston rings.

piston rings: Metal rings located in grooves on the outside of the piston that keep the fuel/air mixture from leaking past the piston into the crankcase during compression and that keep oil from going up into the combustion chamber. Faulty rings can cause poor compression, severe blow-by, and excessive smoking from the tailpipe.

planetary-gear system: A set of gears used in some automatic transmissions that features a central gear, called a sun gear, surrounded by two or more smaller planetary gears that mesh with a ring gear.

polymer coating: A coating that prevents paint from oxidizing, protecting a car from premature fading and rusting. Do-it-yourself polysealants last for six months to a year; professionally applied polyglycotes are touted as lasting from two to five years but haven’t really been around long enough to prove this. See also clear coat.

positive terminal: The battery terminal that leads to the electrical system on vehicles with negative ground . The positive terminal usually has “POS” or “+” on it. Jumper cables and other devices that connect to the battery usually have red clips for the positive terminal and black clips for the negative terminal and ground .

power booster: See brake booster.

power brakes: A brake system that uses a power booster to make braking easier.

power steering: A device that uses hydraulic power to help the driver steer more easily. Vehicles with power steering usually have a reservoir in the power-steering pump, which requires the occasional addition of power-steering fluid (sometimes automatic transmission fluid ).

powertrain control module (PCM): A computer that controls the operation of the fuel, ignition, and emissions control systems on newer vehicles. Also called an electronic control module (ECM).

precombustion chamber: A small chamber located outside the combustion chamber of some vehicles in which a small amount of rich fuel/air mixture can be ignited to start the combustion process to increase fuel efficiency and cut emissions. It’s found principally on diesel engines and certain older gasoline engines. Also called prechambers.

pre-ignition: See knocking.

pressure cap: A radiator cap on a coolant recovery system or radiator that allows the cooling system to operate under pressure at higher temperatures for greater efficiency. Safety pressure caps can be used to help release the pressure before the cap is removed in order to prevent injuries due to escaping steam or hot coolant.

pressure plate: A disc that’s forced by springs against the clutch disk, which forces the disc and the engine flywheel against each other, causing the engine and the transmission to turn at the same rate of speed. See also clutch.

psi: The abbreviation for pounds per square inch, a measurement of pressure. The term is used to measure the amount of air pressure in tires and the amount of compression of the fuel/air mixture in the combustion chamber, etc. In the metric system, pressure is measured by kilograms per square centimeter.

pulse width: See injector pulse width.

push rods: The rods that run between the camshaft lifters and the rocker arms. The lifters and the push rods are pushed up by the cam lobes, causing the rocker arms to make the valves open and close. Engines with overhead cams don’t need push rods because the camshaft cam lobes contact the valves or rocker arms directly.

race: A metal ring surrounding the balls or rollers of a wheel bearing, allowing them to turn against its smooth surface.

radial tires: See tires.

radiator: A device that cools the liquid in the cooling system by allowing it to circulate through a series of water channels that are exposed to air ducts.

radiator cap: See pressure cap.

radiator fill hole: An opening at the top of the radiator through which a 50-50 mix of water and coolant can be added if there’s no coolant recovery system. The pressure cap seals the fill hole.

radiator pressure cap: See pressure cap.

R&R: A common term used by service facilities for “removal and replacement” of parts in order to access the site of needed repairs.

ratchet: A device that allows you to turn a screw or bolt in one direction and then move the handle of the wrench or screwdriver back, without force, in the opposite direction to prepare for the next stroke without removing the tool from the screw or bolt. See also socket wrench.

rear axle ratio: The number of times the rear wheels turn compared to a particular transmission speed. The higher the rear axle ratio, the slower the engine can run and still allow the vehicle to achieve a given speed.

rear-wheel drive: A vehicle that’s pushed by its rear wheels rather than pulled by its front wheels has rear-wheel drive. See also front-wheel drive, all-wheel drive, and four-wheel drive.

rebuilt: See rebuild.

rebuild: To disassemble a device, clean it thoroughly, replace worn parts, and reassemble it. Engines, clutches, carburetors, and brakes are sometimes rebuilt as part of the maintenance or restoration of older vehicles. You can rebuild certain parts yourself with a kit containing instructions and part replacements, or you can buy a rebuilt part and turn in your old part for a core charge. Rebuilding is sometimes called overhauling. See also remanufactured.

regenerative braking system: Brakes found on EV s and hybrid vehicles that generate energy and feed it to the battery that powers the electric motor. See also brake system.

remanufactured: A part or engine that has been completely refurbished with new parts—as opposed to a rebuild, where only worn or defective parts are replaced.

replacement parts: Parts made by independent companies called aftermarket suppliers. These parts can range from poor to as good as OEM (original equipment manufacturer).

reproduction: A vehicle or part that has been duplicated by other manufacturers because the original is no longer widely available. See also NOS (new old stock) and OEM (original equipment manufacturer).

resonator: A small auxiliary muffler found on some vehicles that further reduces the noise of the escaping exhaust gases, or “tunes” the exhaust tone, to make a four-cylinder engine sound more like a V-8, for instance.

restoration: Restoring a vehicle to its original condition (including original parts, paint, rechroming, and so on) rather than merely rebuilding or repairing one. See also NOS (new old stock), OEM (original equipment manufacturer), reproduction, rebuild, and cherry condition.

retreads: Used tires that have been refurbished by grinding the tread off and replacing it. Not used much on passenger vehicles. The quality of retreads can vary; to be safe, only buy retreads from well-known manufacturers.

rings: See piston rings.

rocker arm cover: A metal lid located on top of the cylinder head on vehicles that have valves activated by an overhead cam or rocker arms. See also valve cover.

rocker arms: Curved levers, each of which has one end contacting a push rod and the other end bearing on a valve stem in order to make the valves open in response to the pressure of the cam lobes on the spinning camshaft and close from the pressure of the valve spring. Cars with overhead cams don’t always require rocker arms because the valve stems may have lifters that contact the cam lobes directly.

rollover stability control (RSC): A safety system that identifies situations in which a vehicle that’s taking a turn too sharply or too fast could roll over, and then helps to prevent the rollover.

rotor: A device on vehicles with ignition systems with distributors that sits on top of the distributor shaft and rotates with it to conduct electric current to each spark plug terminal in turn. The discs on disc brakes are also referred to as rotors, as is the triangular device inside a rotary engine that revolves, creating smaller chambers where the four-stroke power cycle takes place. See also ignition system.

rpm: The abbreviation for revolutions per minute.

rubber: All the rubber seals, mats, and pads that cushion and protect car windows, trim, handles, bumper sections, carpets, and so on. A restoration should include replacement of all damaged or missing rubber with OEM (original equipment manufacturer) rubber parts or exact reproductions.

rubbing compound: A polish that contains abrasives harsh enough to remove layers of dead paint. Useful in radical restoration procedures, rubbing compounds shouldn’t be used on new vehicles with clear coats or delicate finishes.

safety pressure cap: See radiator pressure cap.

sealed beam unit: A headlight that contains high- or low-beam filaments or both, a reflector, and a lens. It is sealed to keep out dirt and moisture. When the headlight fails, you replace the entire unit. Sealed beam units usually are found on older vehicles. Newer vehicles have small bulbs or high intensity discharge lamps (HID) filled with halogen or xenon gas.

sealer: A substance added to the liquid in the cooling system to seal small leaks; also called stop-leak. Other kinds of sealing compounds are used to coat surfaces before installing hoses or gaskets. These are effective in preventing leakage but usually make the hose or gasket hard to remove.

sensors: Electronic devices that monitor conditions such as fuel pressure, intake air temperature, throttle position, wheel speed with anti-lock braking systems (ABS), electronic stability control, rollover stability control (RSC), and traction control systems, engine speed, and load. This data is fed to the engine control unit (ECU), which controls a variety of system management computers.

serpentine belt: See accessory belt.

service manual: A handbook published by a car manufacturer or a specialized publishing company that contains instructions and specifications for the maintenance and repair of specific vehicles. Most deal with only one make, model, or year. Although intended for professionals or very experienced amateurs, service manuals are useful for locating various parts on your vehicle and for parts specifications. It’s good to carry one in case of a breakdown in an area where local technicians may be unfamiliar with your vehicle. If you don’t want to buy one, ask your local library to find one you can borrow. See also owner’s manual.

service writer: The person responsible for receiving vehicles brought to the service department at dealerships. He or she estimates the nature and cost of repairs and when the work will be completed.

shims: Thin pieces of metal used between parts to fill gaps or level them.

shock absorbers: Devices located near each wheel to cut down the vertical bouncing of the passenger compartment on the springs after the wheels go over a bump or the vehicle stops short. Shock absorbers also improve handling on rough road surfaces. See also suspension system and stabilizing system.

sludge: A combination of oxidized oil, gasoline, coolant, and blow-by that can foul an engine. Modern engine oils have detergents to break down sludge.

socket wrench: A wrench that completely covers the head of a bolt rather than fitting around its circumference. A socket set usually consists of a variety of sockets, at least one handle (usually a ratchet handle), a couple of extenders, and sometimes a spark plug socket as well.

solenoid: A device connected to electrical current that induces mechanical movement in another device. See also starter solenoid.

spark plug: A device that delivers the electrical spark to the combustion chamber. The spark ignites the fuel/air mixture and produces the power that drives the engine. See also ignition system , and spark plug gap.

spark plug gap: The space between the center and side spark plug electrodes, across which the spark must jump to ignite the fuel/air mixture in the combustion chamber. Adjusting this gap is a major part of the basic tune-up because the width of the gap affects the intensity of the spark. See also feeler gauge.

spark plug socket: A metal cylinder with a rubber lining that fits over the exposed end of the spark plug to make it easy to remove the plug without damaging its porcelain surface. This socket can be purchased separately or as part of a socket wrench set.

specifications: The size, description, or part numbers for various items needed to maintain or repair a vehicle; often referred to as specs. See also owner’s manual and service manual.

speedometer: A dashboard device that measures and indicates how fast the vehicle is going. If a vehicle has a speedometer cable, it should be lubricated when the needle starts to move erratically or if the cable begins to make noise. Electronic speedometers on many modern vehicles don’t have cables.

spindle: The small shaft located at each front wheel on which the front wheels revolve on rear-wheel drive vehicles.

splash shield: A removable device found on disc brakes that helps to keep water and dirt from fouling the brakes.

springs: Devices to cushion and absorb shocks and bumps and to keep the vehicle level on turns. A vehicle can have air springs, leaf springs, coil springs, or a combination of these. See also suspension system.

stabilizers: A variety of devices used to keep the passenger compartment of a vehicle from swaying and lurching on sharp curves and turns. Also known as sway bars. See also suspension system.

standard transmission: See manual transmission.

starter: A small electrical motor that causes the engine crankshaft to begin to turn, which starts the engine running and so starts the car. See also starting system.

starter solenoid: A device that uses electrical current to start and engage the starter. See also solenoid.

starting system: The portion of the electrical system that starts the car. Consists of the ignition switch, which closes the circuit and allows current to flow from the battery to the starter via the starter solenoid and in some cases a relay. It’s also called the cranking circuit.

steering-axis inclination: An alignment adjustment that allows the steering wheel to return to the straight-ahead position when the vehicle comes out of a turn.

steering knuckles: A type of ball joint located at the ends of the tie rods on the steering linkage. See also grease fittings.

steering linkage: The system that connects the steering wheel to the front wheels and allows the wheels to change direction in response to commands from the driver. It contains grease fittings to cushion against wear and friction. See also alignment.

steering ratio: The relationship between how far you turn the steering wheel and how far the wheels actually turn.

steering system: A series of linkages and gears that link the driver to the wheels.

stick shift: See gearshift.

straight engine: See in-line engine.

stroke: The vertical distance that the piston moves as it travels from the top to the bottom or from the bottom to the top of the cylinder. See also bore and four-stroke power cycle.

strut: An efficient type of shock absorber. See also suspension system.

supercharging: A method of increasing engine power by forcing larger amounts of air into the cylinders using an accessory belt -driven air compressor (also called a blower). Unlike turbocharging, which uses air compressed by an exhaust-driven turbine, supercharging decreases fuel economy.

suspension system: A system that cushions the passenger compartment of the vehicle from the bumps and shocks caused by the wheels moving over irregular road surfaces. The system includes springs or torsion bars, shock absorbers, steering linkage, upper and lower control arms, and stabilizers.

synchromesh: A manual transmission device that allows two gears to mesh more smoothly by causing them to spin at the same rate of speed before coming together.

system management computers: Computers that control various systems and features on a vehicle. See also engine control unit (ECU), electronic sensing device, and transmission controller.

tachometer: A device for measuring engine rpm. Many vehicles with manual transmissions have a dashboard tachometer to aid in changing gears. Most cars with automatic transmissions also have tachs these days because owners seem to expect them.

tailpipe: The last link in the exhaust system. It conducts exhaust gases from the muffler to the rear of the vehicle and into the atmosphere.

telematics: A word derived from combining “telecommunication” and “informatics,” it’s the technical term for the wireless systems that enable your vehicle to communicate with the outside world.

thermostat: A device that keeps the hot coolant confined to the engine cooling passages to help the engine warm up more quickly. After the engine has warmed up, the thermostat allows the coolant to flow to the radiator, where it’s cooled and recirculated through the engine to prevent overheating. See also cooling system.

throttle: A device that controls the power produced by a gasoline engine at any given moment by regulating the amount that goes into the cylinders. Mechanical throttles consist of a throttle arm located on the outside of the throttle-body on fuel injection systems. The throttle arm is connected to the accelerator pedal, which activates a throttle valve where it joins the intake manifold. Electronic or throttle-by-wire systems use a sensor on the accelerator pedal to send an electronic signal to the fuel injection system telling it how much fuel to spray into the cylinders based on demand from the accelerator.

throw-out bearing: A part of the clutch, activated by the clutch pedal, that allows the clutch to disengage. If you allow the car to idle in gear with the clutch pedal depressed instead of shifting to Neutral, you can wear out the throw-out bearing. Also called the clutch release bearing. See also pedal free-play.

tie rods: Parts of a rack-and-pinion steering linkage that connect the rack to the steering arm.

timing: The capability of the valves, ignition system, and other engine-driven parts of the vehicle to work together for maximum efficiency. On older cars, timing is checked as part of the basic tune-up because if the timing is off, the vehicle can’t perform well.

timing belt: A crankshaft -driven, toothed belt that drives an overhead cam or camshafts and, in some vehicles, a water pump. This belt should be changed at the mileage interval recommended in your owner’s manual.

timing chain: A crankshaft -driven chain that drives the camshaft(s), which in turn open and close the intake and exhaust valves. In many modern vehicles, this part has been replaced by a timing belt. See also valve timing.

tire valve: A small valve mounted on the wheel rims of tires that allows air to be added to the tire with a properly equipped air hose and allows air to be withdrawn from an over-inflated tire by pressing on the little stem at the end of the valve. Tire valves should have caps to protect against leaks and to keep dirt from fouling the valve.

tires: Critical parts of your vehicle that allow braking, accelerating, and cornering on wet or dry roads and contribute significantly to the quality of the ride. All passenger vehicles today use radial construction tires. Sidewalls are usually reinforced with polyester, fiberglass, steel, or nylon. Treads are reinforced with a combination of polyester, steel, and sometimes nylon. See also alignment, ozone checking, retreads, and tire valve.

toe-in: An adjustment of front-wheel alignment so that the tires are slightly pigeon-toed when the vehicle is standing still. Toe-in is required for proper steering and tire wear.

toe-out: A wheel alignment angle used to control the way the vehicle tracks on turns. Tires should never be toe-out.

torque: Turning or twisting force. See also torque wrench.

torque converter: A fluid coupling in an automatic transmission that transfers power from the engine to the transmission input shaft .

torque wrench: A special wrench that measures the exact amount of torque being applied to tighten a nut or bolt.

torsion bars: See suspension system.

traction control system (TCS): A feature that senses when one wheel is spinning faster than the others and corrects it by automatically applying the brakes, cutting off power to that wheel, and/or reducing acceleration to improve traction and maintain stability. See also anti-lock braking system (ABS) and electronic stability control (ESC).

trailer-towing packages: Optional equipment that usually includes a heavy-duty suspension, a larger radiator, and a rear bumper with a trailer hitch and wiring for the tow vehicle’s lights.

transaxle: A single unit combining the transmission and the differential. The transaxle connects directly to the driveshafts on front-wheel drive or rear-engine vehicles.

transfer case: A unit mounted between the transmission and driveshaft of four-wheel drive vehicles that controls the flow of power to the front and rear drive axles when you shift back and forth between two-wheel and four-wheel drive.

transistor: A tiny electronic component with at least three connections but no moving parts that functions as a switch or amplifier, by controlling the flow of current.

transmission: Typically an assembly of toothed gears that mesh in varying arrangements to enable your vehicle to move forward and backward with varying amounts of power to meet a variety of driving situations. Manual transmissions are operated by means of a clutch and gearshift. Automatic transmissions are driven by hydraulic pressure. Continuously variable transmissions (CVT) are automatic transmissions that use pulleys instead of toothed gears.

transmission controller: A computer found on electronic transmissions that controls shifting by monitoring engine speed, load, and other factors. See also system management computers.

transmission fluid: A thin oil that fills the automatic transmission so that it can run on hydraulic pressure. It’s also found in many power-steering pumps.

transmission input shaft: The turning shaft that carries the power from the engine and torque converter or clutch into the transmission.

transmission output shaft: The turning shaft that carries the power out of the transmission to the driveshaft.

transverse engine: An engine that’s mounted between the drive wheels with its cylinders running parallel to the wheels. Most front-wheel drive vehicles have transverse engines.

trim: Nonfunctional metal or plastic moldings, frames, and other decorative additions to vehicle bodies and interiors.

tune-up: The process of replacing fuel filters, air filters, and spark plugs to ensure that air, fuel, and spark are available in good condition to obtain maximum engine efficiency.

turbocharging: Using an exhaust-driven turbine to compress air and drive it into the cylinders in order to increase the power of the engine. See also supercharging.

turn over: An engine is said to turn over when the starter has caused the crankshaft to begin to turn, which starts the pistons moving so that combustion can begin to take place in the cylinders, providing power to move the vehicle.

turning radius: A measure of how tightly a vehicle can turn when the steering wheel is held all the way in one direction.

U-joints: An abbreviation for universal joints.

undercoating: A protective material applied to the undersides of new vehicles to prevent the formation of rust.

universal joints: Couplings located at either end of the driveshaft on a rear-wheel drive vehicle that allow the shaft to move freely without affecting the more rigid transmission shaft and to absorb the movement of the axle and wheels. Also called U-joints. On cars with transverse engines, these are called constant velocity joints (CV).

vacuum modulator: A device found on some older automatic transmissions which controls the pressure in the transmission’s hydraulic system. If the vacuum modulator malfunctions, it can give the impression of transmission failure or can leak transmission fluid into the intake manifold, producing smoke at the tailpipe.

valve cover: A metal lid located on top of the cylinder head on vehicles with overhead valves. The valve cover is removed when adjustable valves need adjusting.

valves: Found in the cylinder head , valves open and close to allow fuel and air to enter the combustion chamber and exhaust gases to leave it. They are opened by means of valve lifters, push rods, rocker arms, and overhead camshaft lobes, and closed by springs. See also exhaust valve, intake valve, timing belt, and timing chain.

vaporize: To convert a liquid into a mist by breaking it into small particles and mixing it with air. Fuel injector nozzles spray tiny amounts of gasoline or other fuel into the ignition chamber, vaporizing it to produce a combustible fuel/air mixture.

VIN (vehicle identification number): A unique number found on the left-hand corner where the dashboard meets the window as well as on the registration and other paperwork for each vehicle.

viscosity: The thickness or pourability of a liquid. Oil comes in a variety of thicknesses, or weights, as well as in single viscosity (single-weight oil) and in a blend of viscosities (multi-weight oil), which enable it to flow easily in cold weather and reduce thinning in hot weather. The higher the weight, the greater the viscosity of the oil. You can find the weight of the oil on the outside of the bottle.

voltage regulator: An electrical device that controls or regulates the electric voltage generated by the alternator. On many vehicles this is an integral part of the alternator rather than a separate component, or this function may be performed by the PCM.

V-type engine: An engine in which the cylinders occur in two rows set at an angle to each other, with the crankshaft running through the point of the V. V-type engines are identified by number of cylinders as V6, V8, and so on.

warning lights: See malfunction indicator lights (MIL).

warranty: A promise by an automaker or dealership to fix or replace parts on a new vehicle if they malfunction before a specific time or distance has elapsed. See also guarantee.

water jackets: Channels in the engine through which water and coolant (antifreeze) circulate to cool the engine. See also cooling system.

water pump: A device that circulates the liquid through the cooling system by pumping it from the engine water jackets to the radiator.

water separator: A device found on diesel vehicles that removes any water that may have contaminated the diesel fuel.

wheel alignment: See alignment.

wheel balancing: A procedure that ensures that the weight of a wheel and tire assembly is distributed evenly so that your vehicle moves smoothly at any speed, with no vibration in the steering wheel or other areas. Usually, the wheel and tire assembly is removed from the vehicle and placed on a balancing machine, which measures imbalance and indicates the points around the rim where small weights must be mounted in order to make the wheel vibration-free, especially at highway speeds.

wheel bearings: The inner and outer bearings found at each wheel that cushion the contact between the wheel and the spindle it sits on. They’re packed with grease to prevent wear from the friction produced by the turning wheels. See also bearings.

wheel cylinder: On drum brake systems, a small cylinder, located at each wheel brake, that uses brake fluid to exert hydraulic pressure, which forces the brake shoes against the brake drums and stops the vehicle. See also calipers.

zero-emission vehicles (ZEV): Vehicles that produce no emissions when running. Some state laws mandating the production of ZEVs, especially in California, have motivated carmakers to comply, mostly by accelerated research and development of electric vehicles (EV). See also partial zero-emission vehicles (PZEV).