Frequently Used Automotive Terms

Frequently Used Automotive Terms
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A
Adaptive cruise control (ACC): An advanced cruise control system that maintains a preset distance or
time interval from the vehicle ahead by automatically controlling the brakes and throttle.
Adaptive headlights: Headlights that steer in the direction the front wheels are turned to improve
visibility when going around corners.
Advanced Driver Assistance Systems (ADAS): A variety of safety-related systems that monitor
vehicle performance and the surrounding environment. ADAS provide a variety of driver alerts when
potentially hazardous conditions exists, and some (such as automatic emergency braking) can take
corrective action if the driver fails to respond appropriately to a dangerous situation.
Air filter: A paper or fabric baffle that captures dust, dirt and debris from the intake airstream to prevent
it from entering the engine.
Aftermarket part: Any service replacement part not obtained from the vehicle manufacturer through a
franchised dealer. Many aftermarket parts are made by the same companies that supply the original
equipment part to the vehicle manufacturer.
All-wheel drive (AWD): A permanent, four-wheel drive system designed for improved traction on all
surfaces and at all times. The main difference between AWD and 4WD systems is that the driver cannot
disengage AWD.
Anti-freeze (coolant): The liquid in the engine cooling system that dissipates heat. Engine coolant
prevents freeze-up in winter, raises the boiling point in summer, and protects the cooling system from
rust and corrosion year round.
Anti-lock braking system (ABS): System that prevents wheel lock-up by automatically regulating the
brakes. ABS can decrease braking distances on slippery pavement, prevent skidding and provide greater
control during sudden stops.
A-Pillar: The roof support pillar at either side of the windshield.
Around view: A series of cameras that provide an overhead 360-degree view of the area immediately
surrounding the vehicle via a screen on the dashboard.
Automatic emergency braking (AEB): A system that automatically applies the brakes to prevent or
mitigate a collision when the car is approaching another vehicle or object at too high a rate of speed.
Autonomous vehicle (AV): A car that uses advanced technology to accelerate, brake and steer itself.
There are six levels of vehicle autonomy designated by SAE Standard J3016.
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Autopilot: The name Tesla uses for their semi-autonomous vehicle driving system.
Axle shaft: On front-wheel drive vehicles, the shafts that connect the transaxle to the driven wheels.
Axle shafts are also used on some rear-wheel drive vehicles with independent suspensions to connect
the differential assembly to the driven wheels. Axle shafts commonly have a universal joint at each end
to accommodate suspension movement. In front-wheel drive applications, constant velocity joints are
used that smooth power delivery and allow the wheels to be turned for steering.
B
Backfire: Gunshot-like sound from the engine air intake or tailpipe.
Backlash: The amount of free play between two moving parts. Commonly used in reference to the
clearance between two gears that mesh with one another.
Balancing (tires): Adding small amounts of weight to a wheel to offset any imbalance present in the tire
and wheel assembly. Proper balance eliminates wheel and tire vibrations that are annoying, can reduce
traction in certain circumstances and cause increased tire and suspension wear.
Battery: The component that stores the electrical power needed to start the engine. The battery also
powers vehicle accessories when there is insufficient power output from the charging system, and acts
as a “shock absorber” for the vehicle electrical system.
Battery acid (electrolyte): The fluid in automotive batteries, a mixture of sulfuric acid and water.
Battery Electric Vehicle (BEV): A car without an internal combustion engine that is powered exclusively
by electricity stored in a large onboard battery pack. Many BEVs, such as the Nissan Leaf, have a driving
range of about 60-100 miles. However, the Chevrolet Bolt and all Tesla models have larger battery packs
that offer driving ranges of 140 to 300+ miles.
Battery hold-down: A fastening device used to secure the battery firmly in place. The two most common
types are a wedge that clamps over a protrusion near the bottom of the battery, or a bracket that fits
around or across the top of the battery and is secured with long threaded rods.
Bearing: a component that reduces friction and wear between two moving parts. There are several types
of bearings. Engine crankshafts generally use plain bearings, while other rotating components commonly
use ball- or roller-bearings.
Biodiesel: Vegetable oil- or animal fat-based diesel fuel. Biodiesel is typically blended with petroleumbased diesel fuel in 5 or 20 percent concentrations that are commonly referred to as B5 and B20.
Blind spot monitoring: An ADAS system that monitors the driver’s blind spots at the rear quarters of
the car and provides audible, visual and/or tactile alerts when a vehicle is present in them.
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Bottoming: When your vehicle reaches the limits of the suspension travel (such as when going over
bumps), and the vehicle’s springs are completely compressed. This results in a sudden transfer of
noise/harshness, particularly through the steering, and possible contact of the vehicle undercarriage with
the pavement.
B-Pillar: The roof support pillars closest to the driver’s and front-seat passenger’s heads at the rear of
the front doors. “Hardtop” cars do not have B-pillars.
Brake Assist: An ADAS system that automatically applies full braking power when it detects that the
driver is executing a panic stop.
Brake booster: A vacuum or hydraulic powered device that multiplies the foot pressure applied to the
brake pedal to increase braking power while reducing the required driver effort.
Brake caliper: The hydraulic assembly that contains the brake pads and applies them against the brake
rotor to slow or stop the car.
Brake drag: Brakes that do not completely release after application.
Brake drum: A cylindrical component that mounts on the wheel hub and has a machined inner surface
that the brake shoes press against to slow or stop the vehicle.
Brake fade: A loss of braking efficiency caused by high brake temperatures. Fade typically occurs during
extended and/or repeated heavy brake usage. Brake fade requires increased pedal pressure to maintain
the same level of braking action. In extreme cases, the brake pedal may sink to the floor causing a near
total loss of braking ability.
Brake fluid: The liquid in the brake system that acts as a hydraulic fluid. As you step on the brake pedal,
brake fluid is forced through the system to apply the brake assemblies at the wheels.
Brake fluid reservoir: The container that stores a supply of brake fluid until it is needed. On most
vehicles, the reservoir is mounted on the brake master cylinder.
Brake master cylinder: The brake system component that turns the mechanical power provided when
you step on the brake pedal into the hydraulic power that is needed to apply the brakes and slow or stop
the vehicle.
Brake rotor: A flat disc that mounts on the wheel hub and has machined outer surfaces that the brake
pads press against to slow or stop the vehicle.
Brake shoes: Curved metal platforms faced with a friction material that is pressed against the inside of a
brake drum to slow or stop the car. Brake shoes are applied by the wheel cylinder.
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Brake pads: Metal backing plates faced with a friction material that is pressed against a brake rotor to
slow or stop the car. The brake pads fit into, and are applied by, brake calipers.
Bucking: Engine miss or hesitation, or transmission slip then engagement, that causes the car to lurch
repeatedly as it accelerates.
Bushing: A cylindrical metal sleeve with a hole through its center. Bushings are used to guide and
support various moving parts on automobiles. Bushings are often made of bronze and, while sometimes
lightly lubricated with oil or grease, depend primarily on the strength and frictional properties of the metal
itself for durability.
C
Cabin: The interior of the vehicle where the driver and passengers sit.
Camber: The angle at which wheel and tire assembly tilts in (negative) or out (positive) from vertical.
Typically measured and adjusted as part of a wheel alignment.
Camshaft: A machined shaft with eccentric lobes that are used to open the valves in the engine cylinder
head(s).
Caster: The angle at which the kingpin axis of the vehicle suspension tilts forward (negative) or rearward
(positive) from vertical. Typically measured and adjusted as part of a wheel alignment.
Catalytic converter: An emission control device in the exhaust system that uses chemical oxidation and
reduction processes to cleanse the engine exhaust gasses before they leave the tailpipe.
Chassis (undercarriage): The vehicle frame that carries all suspension and power train components.
Most trucks still use a frame that is separate from the body, but virtually all modern passenger cars use
unit-body construction in which the body itself serves as the main chassis member.
Clutch: A mechanism that can couple and uncouple two rotating parts. With manual transmissions, a
clutch between the engine and gearbox makes shifting easier and allows the car to be brought to a stop
with the engine running.
Cold cranking amps (CCA): A rating that indicates the amount of power a battery can provide for
engine cranking in cold-start conditions.
Compressed Natural Gas (CNG): A purified and pressurized version of natural gas suitable for use as
an automotive fuel. Most light-duty vehicles that can use CNG have a “bi-fuel” system that allows
operation on either gasoline or CNG.
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Coolant (anti-freeze): The liquid in the engine cooling system that dissipates heat. Engine coolant
prevents freeze-up in winter, raises the boiling point in summer, and protects the cooling system from
rust and corrosion year round.
Coolant recovery reservoir: A tank that stores additional engine coolant and allows the radiator to be
completely filled at all times for maximum efficiency. As the engine warms up and the coolant expands,
excess is directed to the reservoir. As the engine cools and the coolant contracts, surplus in the reservoir
is drawn back into the radiator.
Compression ratio: The ratio between the largest and smallest possible volumes in the cylinder of an
internal-combustion engine. For example, a compression ratio of 9:1 means the piston will compress the
air/fuel mixture into a space that is nine times smaller than the maximum cylinder volume.
Constant velocity (CV) joint: Typically used in front-wheel drive applications, constant velocity joints
are a form of universal joint that smoothes power delivery and allows wheels to be turned for steering.
Continuously Variable Transmission (CVT): an automatic transmission that uses two variablediameter pulleys and a steel belt to continuously alter its gear ratio. This provides smooth power delivery
and allows the engine to operate at the optimum speed for any given driving condition.
Control arms: Pivoting suspension components that connect the vehicle chassis to the spindle that
supports the wheel and tire assembly.
Cowl: The area on the vehicle body at the base of the windshield.
C-Pillar: The roof support pillars at the sides of the rear window. On four-door station wagons, the Cpillars are at the back of the rear doors, and the pillars adjacent to the rear window become D-pillars.
Crank: The car “cranks” when the starter motor is able to spin the engine or cause it to “turn over.” If the
car “will not crank” when you turn the ignition key, you hear either a clicking sound, or nothing at all. The
term “crank” is also used as a short form of the word crankshaft.
Crankcase (engine block): Largest assembly of an internal combustion engine. Consists of the lower
part of the engine, which contains the crankshaft, connecting rods and pistons in an oil-tight housing.
Crankshaft: The central machined shaft in an internal combustion engine. The crankshaft converts the
reciprocating motion of the pistons and connecting rods into rotary motion that is directed to the
transmission and ultimately to the wheels.
Curb weight: The weight of a vehicle carrying a full tank of fuel but no passengers or cargo.
Cuts out: When an engine loses power or misfires and feels like the engine is shut off momentarily.
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Crossover Utility Vehicle (CUV): A vehicle similar to an SUV but built with unit-body construction (no
separate frame) and often based on existing passenger car structures. CUVs offer styling similar to that
of an SUV, but come in various sizes with fuel economy, ride and handling more like a sedan than a
truck. CUVs are typically used as “people-haulers” and most have less off-road capabilities than more
conventional SUVs.
D
Daytime Running Lights (DRL): Front lighting designed to operate during daylight hours to improve a
vehicle’s visibility to other drivers. DRLs may be normal-intensity headlights, reduced-intensity headlights
or separate lighting assemblies that may include LED arrays.
Detonation (knock, ping): Rapid, uncontrolled combustion of the air-fuel mixture in the cylinder that
results in a hard, rattling sound. Detonation can cause severe engine damage if left unchecked for long.
Diesel (engine): An engine design in which the fuel is ignited by heat generated in compressing air
rather than by a spark plug as in a gasoline engine. Diesel engines are more efficient than gasoline
engines, and provide more torque at lower rpm. Modern “clean diesels” meet the same emission
standards as gasoline engines and require the use of ultra-low sulfur diesel (USLD) fuel, which has been
mandated for on-road diesels since 2007.
Dieseling: When the engine continues to run for a short time after the ignition is turned off. Caused by
high combustion chamber temperatures igniting residual fuel drawn into the cylinders. Usually occurs
only on older carbureted engines.
Differential: A system of gears that allows the outside driven wheel to rotate faster than the inside driven
wheel when turning a corner. Conventional “open” differentials direct engine power to the wheel with the
least traction, which can be a problem on slippery surfaces. To combat this, some vehicles are equipped
with “limited-slip” differentials that ensure some power is always delivered to both driven wheels.
Differential lube (gear oil): Heavy-duty lubricant specifically designed to handle the requirements of the
gears and mechanisms located within the differential case.
Dipstick: Calibrated rod used to measure the level of a fluid. On automobiles, dipsticks are commonly
used to check the oil level in the engine, transmission and power steering reservoir.
Disc brake: Brake design in which brake pads press against a disc (commonly called the brake rotor) to
slow or stop the vehicle.
Driveability: An assessment of vehicle operation that takes into account how well all systems function
and integrate with one another for a seamless driving experience. Most commonly used in reference to
powertrain operation across a wide range of temperatures and load conditions.
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Driver alertness monitoring: An ADAS system that monitors driver behavior for indications of drowsy or
distracted driving. When warranted, the system provides visual and audible alerts advising the drive to
take make a rest stop.
Drivetrain (powertrain): The combination of the engine, transmission, driveshaft, differential and axles
that deliver power to the wheels.
Drum brake: Brake design in which brake shoes press against the inside of a cylindrical drum to slow or
stop the vehicle.
Drive shaft: On rear-wheel or all-wheel drive vehicles, the shaft that couples the transmission to the rear
axle differential assembly.
Drive Pilot: The name Mercedes-Benz uses for their semi-autonomous vehicle driving system.
Dual Clutch Transmission (DCT): An automated manual transmission design that uses a pair of
hydraulically-actuated clutches to change between odd-numbered gears on one shaft and evennumbered gears on another. See also Direct-shift Sequential Gearbox and Sequential Manual Gearbox.
Direct-shift Sequential Gearbox (DSG): An automated manual transmission design that uses a pair of
hydraulically-actuated clutches to change between odd-numbered gears on one shaft and evennumbered gears on another. See also Dual Clutch Transmission and Sequential Manual Gearbox.
Dual overhead camshafts (DOHC): An engine with two camshafts located in the upper portion of the
cylinder head.
DUBs: A slang term for twenty-inch (“double dime”) or larger custom wheels fitted with low profile tires
for a custom look. Ride quality can suffer with larger wheels and tires, although a low profile performance
tires may offer an improvement in handling (especially on dry roads) if its diameter is close to that of the
original equipment tire. Tires and wheels more than an inch or two taller than stock can cause ride and
handling to degrade due to their increased weight.
E
Electronic Control Module (ECM): A generic term for an electronic module with computing power used
to control vehicle systems. Modern cars have multiple ECMs that communicate with one another over
vehicle networks.
Electrolyte (battery acid): The fluid in automotive batteries, a mixture of sulfuric acid and water.
Electronic brake force distribution (EBD): A system that helps reduce stopping distances by using
antilock brake system components to vary front-to-rear braking force. The system compensates for
different vehicle loads, and normal weight transfer to the front axle during a stop.
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Electronic fuel injection (EFI): A fuel delivery system in which electrically controlled nozzles (injectors)
spray fuel into the intake manifold or cylinders as needed, allowing for more precise fuel control and
better fuel efficiency than can be achieved with a carburetor.
Electronic Stability Control (ESC): A system that provides selective wheel braking to improve vehicle
handling and help drivers regain control in certain extreme circumstances. ESC employs components of
the anti-lock braking system and is required on all passenger vehicles starting with the 2012 model year.
Systems on SUVs generally also provide incorporate Rollover Mitigation.
Engine block (crankcase): Largest assembly of an internal combustion engine. Consists of the lower
part of the engine that contains the crankshaft, connecting rods and pistons in an oil-tight housing.
Ethanol: Ethyl alcohol sourced primarily from corn that is blended with gasoline in varying proportions
(E10, E85, etc.) to reduce exhaust emissions from older vehicles while supporting energy independence
by reducing the need for imported oil.
Extended-Range Electric Vehicle (EREV): Similar to a plug-in hybrid electric vehicle, an EREV has a
much bigger battery that typically provides an electric-only driving range of around 30 to 40 miles. Once
the battery is discharged, a gasoline engine powers a generator that gives the vehicle an additional 200300 miles of “extended-range” driving. Unlike a PHEV, the gasoline engine in an EREV does not directly
drive the vehicle; it simply provides power to the battery, which continues to propel the car using an
electric motor. The Chevrolet Volt is an example of an EREV.
F
Fast idle: An increased idle speed that typically occurs for a short time after a cold engine start to
improve drivability and speed engine warm up.
Flooding: Excess fuel in the cylinders that makes starting difficult or impossible.
Forward Collision Warning (FCW): A system that provides the driver with an audible, visual and/or
tactile alert when their vehicle’s closing rate with the one ahead indicates a collision may be imminent.
Four-wheel drive (4WD or 4X4): A part-time system that powers all four wheels for improved traction
during adverse road conditions and off-road use. Four-wheel drive systems differ from all-wheel drive
(AWD) systems in two ways: they can be disengaged when not in use, and they are not suitable for use
on dry pavement.
Front-wheel drive (FWD): Drive system that provides power to only the front wheels of the vehicle.
Front-wheel drive systems incorporate a differential into a transmission, creating a transaxle. A transaxle
can be automatic or manual shift.
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Fuel injection (FI): A fuel delivery system in which nozzles (injectors) spray fuel into the intake manifold
or cylinders, allowing for more precise fuel control and better fuel efficiency than can be achieved with a
carburetor. Fuel injection systems come in a variety of forms, but virtually all modern vehicles use some
form of electronic fuel injection.
G
Gasoline Direct Injection (GDI): A fuel delivery system that injects gasoline under extremely high
pressure directly into the engine combustion chamber. This technology generates more power with better
fuel economy and lower emissions.
Gear oil (differential lube): Heavy-duty lubricant specifically designed to handle the requirements of the
gears and mechanisms located within the differential case.
Grab: Brakes engage suddenly and strongly, even when applying light pressure on the brake pedal.
Green House Gas (GHG): Any gas in the atmosphere that absorbs and emits radiation within the
thermal infrared range, thereby contributing to climate change/global warming. The primary greenhouse
gases in the Earth's atmosphere are water vapor, carbon dioxide, methane, nitrous oxide, and ozone.
Gross Vehicle Weight Rating (GVWR): The total maximum allowable weight capacity of a vehicle,
including the weight of the vehicle itself plus the weight of its fuel, passengers, and cargo.
Group number: A number established by the Battery Council International (BCI) that identifies a battery
based on its battery length, height, width, terminal design/location, and other physical characteristics. Not
every battery has a group number as some automakers use custom-sized batteries to fit the underhood
packaging requirements of their cars.
H
Hesitation: Momentary loss of power on acceleration.
High Intensity Discharge (HID) headlights: Headlights that use high voltage to ionize a mix of gases,
including xenon, in a special bulb to produce an extra-white or even bluish light that is several times
brighter than a conventional halogen headlight.
Highly Automated Vehicle (HAV): The National Highway Traffic Safety Administration term for
autonomous vehicles that meet Level 3 and higher performance requirements as specified in SAE
Standard J3016.
Horsepower: The measurement of the engine's ability to produce work.
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Hybrid Electric Vehicle (HEV): A vehicle that achieves improved fuel efficiency by using an electric
motor to help the engine propel the car. The motor receives power from a modestly sized battery that is
automatically recharged during vehicle operation using a generator driven by the car’s engine. The
battery is also recharged by “regenerative braking” that turns the electric motor into a generator during
coasting and braking. HEVs have no provision to connect an external charger, and the energy contained
in the battery can propel the vehicle under electrical power alone for only a very short distance, if at all.
The Toyota Prius is an example of an HEV.
Hydrogen fuel cell: An advanced “battery” that uses hydrogen and oxygen to generate electricity that
powers an electric motor to propel the car. The only exhaust emissions of a hydrogen fuel cell are heat
and water vapor.
I
Infotainment: A combined information and entertainment system that can incorporate audio, video and
various types of data from terrestrial radio, satellite radio, CD/DVD/Blu-ray discs, SD cards, auxiliary
inputs, a factory telematics system and/or a Bluetooth link to a smartphone.
Intermittent: A problem that comes and goes with no obvious pattern.
K
Knock (detonation, ping): Rapid, uncontrolled combustion of the air-fuel mixture in the cylinder that
results in a hard, rattling sound. Knock can cause severe engine damage if left unchecked for long.
L
Lane departure warning (LDW): An ADAS system that monitors lane markings and provides the driver
with audible, visual and/or tactile alerts if their car begins to leave its lane and the turn signal is not on.
Lane keeping assist (LKA): An ADAS system that automatically applies braking and/or steering inputs
to help keep a vehicle in its lane when the turn signal is not on.
Light Emitting Diode (LED) headlights: Headlights that use an array of LEDs to provide forward
illumination. LED headlights provide a “whiter” light than HID units, but they are more directional and may
produce less light overall.
Lightweighting: The process of reducing vehicle weight using high-strength steels, aluminum, plastics,
carbon fiber and other materials to achieve fuel economy gains that reduce greenhouse gas emissions.
Limited-slip (differential): A system of gears that allows the outside driven wheel to rotate faster than
the inside driven wheel when turning a corner. Compared to a conventional “open” differential (which
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directs power to the wheel with the least traction), a “limited-slip” differentials ensure that some power is
always delivered to both driven wheels.
Liquefied Petroleum Gas (LPG): Liquefied petroleum gas, also called propane, is a combustible byproduct of natural gas processing and crude oil refining. LPG has been employed as a motor fuel for over
90 years, and outside the U.S. it often goes by the name “autogas.”
M
Manual transmission: A transmission that requires the driver to change gears using a clutch and a shift
lever.
Master cylinder (brake): The component used to turn mechanical force applied to the brake pedal into
the hydraulic power needed to apply the brakes and slow or stop the vehicle.
Master cylinder (clutch): The component used to turn mechanical force applied to the clutch pedal into
the hydraulic power needed to release the clutch and allow gear changing with a manual transmission.
Miles per gallon (MPG): A measure of fuel efficiency based on the number of miles a vehicle can travel
using one gallon of fuel. Federal fuel economy estimates are based on standardized tests that enable the
use of EPA fuel economy estimates to compare vehicles. See www.fueleconomy.gov.
Miles per gallon equivalent (MPGe): The distance an electric vehicle can travel on the amount of
energy equivalent to that in a gallon of gasoline.
Misfire (miss): The failure of the fuel charge in one or more engine cylinders to ignite, or to ignite at the
proper time.
Multi-point injection: A fuel delivery system that utilizes a separate fuel injector for each cylinder.
N
Night vision: Systems that use active infrared lighting or passive thermographic cameras to detect
people, animals and other warm objects on or adjacent to the road that are beyond what can be seen
with the headlights. Obstacle locations are displayed on a dashboard screen or projected onto the
windshield in front of the driver.
Noise, vibration and harshness (NVH): An acronym used to discuss various operational characteristics
that affect perceived vehicle quality and detract from the driving experience.
O
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On Board Diagnostics (OBD-II): A built-in diagnostic system on all 1996 and newer vehicles that
monitors vehicle emissions control systems for proper operation. Problems that cause an increase in
emissions will illuminate the “check engine” Malfunction Indicator Light (MIL) on the dash. The OBD
system also provides a standardized Diagnostic Link Connector (DLC) for attaching diagnostic tools to
the vehicle.
OE or OEM: Original equipment or original equipment manufacturer. Typically refers to components
used to build the vehicle at the factory, and available as service replacements through franchised
dealers.
P
Park assist: A system of ultrasonic sensors on the front and/or rear bumpers that provide the driver with
audible, visual and/or tactile alerts as their vehicle approaches a stationary object. Also, see self parking.
Pilot Assist: The name Volvo uses for their semi-autonomous vehicle driving system.
Play: Degree of “looseness” in a movable component or series of components. Often used to describe
suspension or steering wear. In the case of steering, play is the amount of free movement at the steering
wheel before the vehicle wheels actually begin to turn.
Plug-in Hybrid Electric Vehicle (PHEV): Similar to a conventional hybrid electric vehicle, a PHEV has a
larger battery that can be charged by plugging the car into an external power source. PHEVs have an
electric-only range of around 10-20 miles. Once that range is exhausted, the vehicle reverts to normal
hybrid operation with a gasoline engine that drives the car and combines with regenerative braking to
charge the battery for a limited amount of electrical power assist. The Toyota Prius Plug-in is an example
of a PHEV.
Port fuel injection: A fuel delivery system that uses a separate fuel injector for each cylinder, and injects
fuel into the intake ports upstream of the intake valves.
Positive crankcase ventilation (PCV) valve: Emission control system that redirects crankcase vapors
back into the engine to be burned. Often controlled by a PCV valve that requires periodic replacement.
PCV valve problems can cause a car to run rough, stall, use excess engine oil, smoke, and have high
exhaust emissions.
Power loss: Engine runs at reduced speed or requires more throttle to maintain constant speed.
Powertrain (drivetrain): The combination of the engine, transmission, driveshaft, differential and axles
that deliver power to the wheels.
Preload: The assembly of two components (often bearings) with a specified amount of pressure
between them so they are prepared to handle the loads that will be applied.
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Pull: When a vehicle self-steers to one side or the other when driving or braking.
R
Radiator: An assembly of tubes and fins that transfer heat from the engine coolant into the passing air
stream. This process is aided by mechanical and/or electrical fans that pull/push additional air through
the radiator as needed.
Rain-sensing wipers: Windshield wipers whose rate of operation is electronically controlled based on
the amount of moisture on the windshield.
Rear cross traffic detection: Sensors at the rear of the vehicle detect approaching traffic or pedestrians
when backing out of a parking space. May be accompanied by or integrated with a rearview camera.
Rear view camera: A camera mounted at the back of the vehicle that displays a picture on a screen in
the dash or rear view mirror of what is behind the car when the transmission is in reverse.
Rear-wheel drive (RWD or 4X2): A drive system that provides power to only the rear wheels of the
vehicle. In trucks, this type of powertrain is sometimes referred to as “4X2” in comparison to a four-wheel
drive “4X4” system.
Recall: A safety- or emissions-related bulletin issued by the vehicle manufacturer, the Environmental
Protection Agency (EPA) or the Department of Transportation (DOT). A recall involves work that must be
done at no charge to the consumer by an authorized dealer of the vehicle make involved.
Revolutions per minute (RPM): The speed at which the engine crankshaft is turning.
Ride: The quality of the vehicle’s movement as it is driven down the road. Based on their intended use,
vehicles can have a variety of different ride characteristics. Factors that affect a vehicle's ride include the
suspension, steering and brakes.
Rough idle: When the engine vibrates or shakes while running with the driver’s foot off the gas.
Rust proofing: Protective coatings applied to vulnerable areas of a vehicle to provide protection against
moisture and road salts that cause rust and corrosion. Tar-based products are typically used on exposed
areas of the undercarriage, while wax-based formulas are used on enclosed areas of the car body such
as doors and fenders.
S
Self parking: A system that identifies potential parking spaces and helps complete parking maneuvers.
All such systems aid in parallel parking and some can also perform pull-in and back-in parking. All of the
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systems control steering, while some can also operate the accelerator, brakes and even transmission
forward and reverse gear selection.
Shift quality: An assessment of how smoothly a transmission, manual or automatic, changes gears.
Shimmy: Side-to-side shaking in the suspension or steering.
Shock absorber: Suspension component that damps spring oscillations. Shock absorbers work by
forcing a fluid through calibrated orifices that limit the rate of movement. Some designs place the fluid
under gas pressure to prevent or reduce fluid foaming that can reduce shock absorber efficiency.
Sidewall: The most visible part of the tire when viewing the vehicle from either side. The sidewall
contains information about the tire size, grade, and ratings as well as the manufacturer's name.
Single overhead camshaft (SOHC): An engine with one camshaft located in the upper portion of the
cylinder head.
Sluggish: Vehicle does not accelerate smoothly or with authority.
Sequential Manual Gearbox (SMG): An automated manual transmission design that uses a pair of
hydraulically-actuated clutches to change between odd-numbered gears on one shaft and evennumbered gears on another. See also Dual Clutch Transmission and Direct-shift Sequential Gearbox.
Specific gravity: Term used in connection with testing a battery's electrolyte. A specific gravity test is
used to determine the battery's state of charge. Sealed “maintenance free” batteries sometimes have an
indicator on top that indicates the state of charge.
Spindle: The suspension component on which the hubs, wheels and tires mount and rotate. Spindles on
the front suspension are turned side to side to steer the vehicle.
Strut (MacPherson strut): A type of shock absorber that also serves as a suspension-locating member.
Most struts incorporate the suspension spring around their shaft, a design called the MacPherson strut. A
“modified strut” mounts the spring separately from the strut.
Stumble: Engine begins to stall but then kicks back in.
Supplemental Restraint System (SRS): A system of passenger protection air bags that supplement the
conventional seatbelts. Some modern cars have more than 10 airbags to protect occupants in frontal,
side and rollover crashes.
Sport Utility Vehicle (SUV): An enclosed body on a truck chassis that provides ruggedness and ground
clearance with room for up to nine passengers and their cargo. These vehicles usually have fuel
Automotive
Glossary
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Repair Dictionary
economy and ride/handling traits similar to the trucks on which they are based. The Chevrolet
Tahoe/Suburban, GMC Yukon/Yukon XL and Ford Expedition/Expedition EL are common SUVs.
Supercharger: An engine driven compressor that forces additional air into the engine, allowing more fuel
to be burned for greater power output.
Surge: Engine speeds up and slows down with no change in accelerator position or brake application by
the driver.
Suspension: The combination of tires, wheels, hubs, spindles, control arms, springs, struts, shock
absorbers and related parts that support the chassis and body as the vehicle moves down the road.
T
Technical service bulletin (TSB): An advisory bulletin issued by a vehicle manufacturer that describes
updated processes and/or parts to address specific problems that may occur on some models. Repairs
based on a TSB are covered under a new-car warranty. However, once the factory warranty has expired,
TSB repairs are performed at the owner’s expense in most cases.
Telematics: The wireless transmission of useful information to and from a vehicle.
Thermostat: A component that helps regulate engine temperature by controlling the speed at which
coolant circulates through the engine.
Tolerance: The maximum size variation between two identical parts. Also, the allowable variation in
clearance between two closely-fit components.
Torque: Twisting force produced by the engine.
Tow: The angle at which the wheels on an axle point inward (tow-in) or outward (tow-out) when the
steering is pointed straight ahead. Typically measured and adjusted as part of a wheel alignment.
Traction Control System (TCS): A system that uses the anti-lock braking components to limit wheel
spin when accelerating on slippery surfaces. More advanced systems can also retard engine spark
timing and automatically back off the throttle when necessary to control wheel spin.
Transaxle: Used in front-wheel drive and rear-engine, rear-wheel drive vehicles. Transaxles incorporate
both a transmission and a differential into a single unit.
Transverse mounted engine: An engine mounted so that its crankshaft is positioned side-to-side in
relation to the vehicle. Transverse engines are typically found in front-wheel drive vehicles.
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Repair Dictionary
Tread: The pattern molded into area of the tire that contacts the road. The tread patterns is designed to
optimize traction based on the tire’s intended use.
Turbocharger: An exhaust-driven supercharger that forces additional air into the engine, allowing more
fuel to be burned for greater power output.
Undercarriage (chassis): The vehicle frame that carries all suspension and power train components.
Most trucks still use a frame that is separate from the body, but virtually all modern passenger cars use
unit-body construction in which the body itself serves as the main chassis member.
U
Universal joint (U-joint): A mechanical coupler that allows a rotating shaft to transmit power over a
range of different angles.
V
Vacuum: The lower than atmospheric pressure that exists in the intake manifold when the engine is
running. On most cars, engine vacuum is used to operate a variety of components and systems.
Vacuum hose: A hose (usually rubber or hard plastic) that transfers vacuum to various vehicle
components.
Variable Valve Timing (VVT): An enhanced engine valve train control system used on most modern
automobiles that allows the lift, duration or timing (any or all) of the intake and/or exhaust valves to be
changed during engine operation. This technology provides smoother operation, more power, better fuel
economy and reduced exhaust emissions.
Vehicle Identification Number (VIN): A 17-character “serial number” that is unique to each vehicle. The
VIN characters are broken down into several sections: the first 3 identify the manufacturer; the next 5 are
vehicle attributes; check digit, model year and plant codes each have their own single identifier; and the
final 6 are the actual sequential number in the vehicle production run.
Vehicle to Infrastructure (V2I): A Dedicated Short Range Communications (DSRC) radio system that
enables cars to receive information from transponders on road signs, traffic signals and other parts of the
transportation infrastructure. Such signals could warn of speed limits, traffic congestion, construction
zones, underpass height limits and more. V2I systems are currently under development.
Vehicle to Vehicle (V2V): A Dedicated Short Range Communications (DSRC) radio system that enables
nearby cars to share information. This technology allows a vehicle to “know” what is happening several
cars ahead, and “see” events taking place outside the driver’s field of view. V2V systems are currently
under development.
Automotive
Glossary
Auto
Repair Dictionary
Vehicle to X (V2X): A “catch all” acronym used to describe V2I, V2V and other similar communication
systems.
Vehicle Identification Number (VIN): The unique 17-character identification number used to identify
modern cars. In addition to the car’s serial number, the VIN provides a variety of additional information
about a vehicle’s construction and components.
Viscosity: The measure of a liquid’s ability to flow under varying temperature conditions. In automobiles,
viscosity most often refers to the “weight” of motor oil, which is designated using number and letter
grades established by the Society of Automotive Engineers. Oils with low numbers such as 5W or 10W
flow easily at low temperatures (the “W” stands for winter). Oils with high numbers such as 30 or 40
resist thinning at high temperatures. Most modern engines call for multi-grade oils such as 5W-30 that
perform well at both low and high temperatures.
W
Water pump: The pump that circulates coolant/antifreeze through the engine, radiator and heater.
Wander: Vehicle tendency to drift from side to side, requiring constant steering corrections by the driver.
Wheelbase: The distance between the centerlines of the front and rear axles of a vehicle.
Wheel cylinder: The hydraulic component in a drum brake assembly that presses the brake shoes
against the drum to slow or stop the car.
Wheel (rim): What the tire is mounted on. Wheels can be made of steel or a light alloy, such as
aluminum.
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