of Automotive Terms
Lost in a world of unfamiliar
terms and jargon? Do you think your mechanic is speaking a foreign
language when he explains what is wrong with your Buick? Well, he
is really, if you don't have a grasp of the basic terms in the world
of cars. We at AutoSpeak can help. We have gathered basic
terms to help you understand better what is going on with your car.
Auto Terms A
- Actual Cash
- The amount of money
invested in the purchase and repairs of a used vehicle. Also known
as ACV, this represents the amount of out of pocket expense a
dealer or broker is "into" a car.
- Air Bag
- The air bag, also
known as a Supplemental Inflatable Restraint System, is a passive
safety device, supplemental to safety belts, that inflates to
provide a cushion to absorb impact forces during moderate to severe
frontal collisions. This system can help to lessen the chance
of contact with the steering wheel, instrument panel and windshield.
The air bag is actuated automatically by sensors located in the
front of the vehicle. To maximize effectiveness, seat and shoulder
belts must always be used in conjunction with this system
- An aerodynamic device
designed to improve traction by increasing the downforce on the
car. The use of airfoils (also called wings) increases the cornering
capability and improves stability at speed, but often at the expense
of additional aerodynamic drag.
- Air Injection
- A system that injects
air into the exhaust ports of the engine for combustion of unburned
hydrocarbons in the exhaust gases, thus producing "cleaner" exhaust
- Generally refers to
wheel alignment, which is the proper adjustment of the car's front
and rear suspension for camber, toe, caster and ride height.
- In the side view,
the foremost roof support of a vehicle, located in most instances
between the outer edge of the windshield and the leading edge
of the front door upper. Also known as an A-Post.
- Alloy Wheels
- A generic term used
to describe any non-steel road wheel. The most common alloy wheels
are cast aluminum. Technically, an alloy is a mixture of two or
more metals. These wheels are known for their light weight and
- Often confused with
Four-Wheel Drive (4WD), this drive system features four, full-time
active drive wheels to reduce wheel slippage and provide greater
driver control over the vehicle. All-Wheel Drive automatically
splits engine torque between the front and rear wheels as needed,
improving on-road traction in unfavorable road conditions. Unlike
Four-Wheel Drive, All-Wheel Drive is an on-road system and is
not designed for off-road use. AWD does not require the driver
to actively engage the system. It is operational at all times,
and requires no switches, lights or visor instructions for system
Brake System (ABS)
- On a vehicle equipped
with Anti-Lock Brakes, the wheels are equipped with speed sensors.
When a sensor determines that a wheel is decelerating so rapidly
that lockup may occur, the electro-Hydraulic Control Unit (EHCU)
is activated. The EHCU then modulates the brake pressure in the
appropriate brake lines by means of the solenoid-operated valves.
This is intended to prevent wheel lockup and help the vehicle
maintain directional stability during potentially hazardous braking
situations. (See also: Rear-Wheel Anti-Lock and Four-Wheel Anti-Lock.)
Locking Front Hubs
- Found in some four-wheel
drive vehicles, this allows the driver to engage, or "lock," the
front axle hubs without leaving the vehicle.
- Axle Ratio
- The ratio between
the rotational speed (RPM) of the drive shaft and that of the
driven wheel. Gear reduction in final drive is determined by dividing
the number of teeth on the ring gear by the number of teeth on
the pinion gear.
Auto Terms B
- The roof support between
a vehicle's front door window and rear side window, if there is
- Balance Shaft
- A shaft designed so
that, as it turns, it counter rotates the rotational direction
of the engine crankshaft in a manner that reduces or cancels out
some of the vibration produced by the engine.
- Ball Joint
- A flexible joint consisting
of a ball within a socket. Ball joints act as pivots which allow
turning of the front wheels and compensate for changes in the
wheel and steering geometries that occur while driving.
- A paint system that
adds a final clear-coat paint layer over primer and color coats
to provide a deep, "wet-look" shine that resists fading.
- Belted Radial
- A reinforcing bank,
normally textile, fiberglass or steel, running around the circumference
of a tire and strengthening the tread area.
- Bias-Ply Tires
- A type of tire in
which the plies or layers of cord in the tire casing are laid
diagonally, criss-crossing one another at an angle of 30 to 40
- A type of automobile
construction in which the body structure is attached to a separate
- The diameter of an
engine cylinder or bearing.
- Brake Fade
- A condition brought
about by repeated brake applications, resulting in build-up of
heat that causes a temporary reduction or fading of braking effectiveness.
- Brake Horsepower
- The actual horsepower
of an engine, measured by a brake attached to the driving shaft
and recorded by a dynamometer.
- Brake Linings
- The replaceable friction
material which contacts the brake drum in a drum brake system
to slow or stop the car.
- Brake Master
- A cylinder containing
a movable piston activated by pressure on the brake pedal. The
piston produces hydraulic pressure that pushes fluid through the
lines and wheel cylinders. This forces the brake lining or pad
against the drum or disc to slow or stop the car.
- Brake Pads
- In a disc system,
they are the replaceable flat segments consisting of a rigid backing
plate plus frictional lining that takes the place of the shoe
and lining in a drum brake. Brake pads are sometimes referred
to as brake pucks.
- Brake Shoe
- The arc-shaped carrier
to which the brake linings are mounted in a drum brake. They also
force the lining against the rotating drum during braking.
- Brakes, Drum
- A type of braking
system that utilizes a metal drum mounted on a wheel to form the
outer shell of a brake. The brake shoes press against the drum
to slow or stop drum and wheel rotation for braking.
- Brakes, Disc
- A type of braking
system in which brake shoes, in a vise-like caliper, grip a revolving
disk mounted on a wheel to slow or stop disc and wheel rotation
Auto Terms C
- The roof support
between a vehicle's rearmost side window and its rear window.
Also known as a C-Post. On a vehicle with four side pillars, the
rearmost roof support may be called a D-pillar.
- The acronym for Corporate
Average Fuel Economy. This single mileage figure is determined
by taking a sales weighted average of the fuel consumption for
all models produced by a manufacturer. The minimum required figure
is an established U. S. government standard. Manufacturers which
do not meet the minimum standard are fined.
- In a disk brake,
a housing for cylinder, pistons and brake shoes, connected to
the hydraulic system. The caliper holds the brake shoes so they
straddle the brake disc.
- Camber Angle
- The inward or outward
angle which a front-wheel spindle makes with a vertical line,
as viewed by either the front or the rear of the vehicle. Positive
camber results when the top of the tire tilts out further than
its bottom. The adjustment of this setting affects both tire wear
and vehicle handling.
- The shaft in the
engine which is driven by gears, belts or chain from the crankshaft.
The camshaft has a series of cams that opens and closes intake
and exhaust valves as it turns.
- The price of the
leased vehicle plus any other charges such as fees or taxes that
become the cost basis for calculating the terms of a lease.
- Caster Angle
- The forward or backward
tilt of the steering axis as viewed from the side. If the point
of load is ahead of the point of contact, the caster angle is
positive. The caster angle tends to keep wheels in a straight
line. Proper caster adjustment improves both tire wear and fuel
- Often simply called
a "catalyst", this is a stainless steel canister that is part
of a vehicle's exhaust system and contains a thin layer of catalytic
material spread over a large area of inert supports. It induces
chemical reactions that convert an engine's exhaust emissions
into less harmful products prior to entering the environment.
- Center of
- Point where the weight
of a vehicle appears to be concentrated and if suspended at that
point would balance front and rear.
- Closed Crankcase
- A system in which
crankcase vapors are discharged into the engine intake system
(usually via the intake manifold) where they are burned during
the combustion process rather than being discharged into the atmosphere.
- Closed End
- A lease in which
the lessee is not responsible for the value of a vehicle when
the lease is done. Under this arrangement the lessee may return
the vehicle at the end of the term and have no further obligation
for the car. Also known as a "walk-away" lease.
- Cold Cranking
- A rating, measured
in amperes. Used for comparing cranking strength of automotive
batteries during extremely cold (0 F or lower) weather.
- The volume of space
at the top of the cylinder where burning of the air/fuel mixture
- Usually manufactured
with replaceable halogen bulbs and separate hard acrylic or glass
lenses. This type of lamp provides superior illumination compared
to the long-conventional sealed beam unit.
- The volume of the
combustion chamber and cylinder when the piston is at the bottom
of its stroke, divided by the volume of the combustion chamber
and cylinder when the piston is at the top of its stroke. Higher
compression ratios tend to increase engine efficiency.
- The machinism is
an air conditioner that pumps vaporized refrigerant out of the
evaporator, compresses it to a relatively high pressure, and then
delivers it to the condenser.
- A device for storing
electrical energy. In A/C application, an air conditioning component
used to remove heat from the inside of a vehicle.
- The metal rod that
connects a piston to the crankshaft.
- Contact Patch
- The area of a tire's
tread that is in contact with the ground.
- Control Arm
- A suspension element
that has one joint at one end and two joints at the other end,
typically on the chassis side. Also known as a wishbone or an
- The mixture of water
and anti-freeze that picks up heat from the engine and transfers
it to the air passing through the radiator. This transfer of heat
keeps the engine operating within its optimum temperature rant
preventing premature engine wear.
- Cooling System
- The system that removes
heat from the engine by the forced circulation of coolant and
thereby prevents engine overheating. In a liquid-cooled engine,
it includes the water jackets, water pump, radiator, and thermostat.
- Cost of Ownership
- Several items enter
into the calculation of how much it actually costs to own a vehicle.
Understanding these items can help determine what is the best
purchase for each person. Ownership costs are divided into fixed
costs and running costs. Fixed costs are the same whether the
car is used or just sits. These costs usually decrease each year.
Running costs are variable and are incurred when the vehicle is
used. Running costs could increase as the vehicle ages.
- A case that encloses
the crankshaft. In most engines, the oil pan and the lower portion
of the cylinder block form the crankcase.
- A shaft with one
or more cranks, or "throws," that are coupled by connecting rods
to the engine's pistons. The combustion process creates reciprocating
motion in the rods and pistons which in turn is converted to a
rotating motion by the crankshaft.
- One of several horizontal
members in a vehicle frame which join the side members and add
to overall strength and stability.
- The basic part of
the engine to which other engine parts are attached. It is usually
a casting and includes engine cylinders and the upper part of
- The removable part
of the engine that attaches to the cylinder block directly above
the cylinders. The head is cast from aluminum or iron and houses
the combustion chambers, the intake and exhaust ports, spark plugs
and much or all of the valve train. It has oil and water passages
for cooling and lubrication.
Auto Terms D
- The vertical or sometimes
diagonal roof supporting member located at the extreme rear of
the roof or greenhouse structure on station wagons and some sedan
- Diesel Engine
- A diesel engine uses
heavier weight components than gas engines to handle higher compression
ratios. Typically, diesel engines run with greater efficiency
and higher torque than similar size gas engines. These attributes
lead to better fuel economy and towing performance. Diesel engines
do not have spark plugs or carburetors. Instead glow plugs are
used to preheat air in the cylinders to ensure easy starts. Once
the engine is started, compression heats the fuel in the cylinders
- A condition in which
gasoline continues to fire after the ignition has been shut off.
In late-model engines, dieseling , or run-on, is caused by heat
and the unusually high manifold pressure that result from retarding
the spark at idle. In fuel-injected cars when the engine is turned
off, fuel is automatically shut off, eliminating dieseling.
- The gear assembly
connected to the drive shaft that permits the wheels to turn at
different speeds when going around a corner, while transmitting
power from the drive shaft to the wheel axles.
- The same attributes
of a standard differential, except that when one wheel is slipping,
the most torque is supplied to the wheel with best traction. A
locking differential reduces the possibility of a vehicle becoming
immobile when one driving wheel loses traction.
- A vehicle's ability
to maintain a true course of travel despite bumps, crosswinds,
uneven road surfaces.
- Disc Brakes
- Properly called caliper
disc brakes, a type of brake that consists of a rotor that rotates
at wheel speed, straddled by a caliper that can squeeze the surfaces
of the rotor with brake pads near its edge. Disc brakes provide
a more linear response and operate more efficiently at high temperatures
and during wet weather than drum brakes.
- In an engine, the
total volume of air or air-fuel mixture an engine is theoretically
capable of drawing into all cylinders during one operating cycle.
Generally expressed in liters or cubic inches. Engine displacement
is equal to (bore) x (bore) x (stroke) x (number of pistons) x
- A component of the
ignition system, usually driven by the camshaft that directs high-voltage
surges to the spark plugs in the proper sequence.
- Double Wishbone
Suspension ("A" Arm Suspension)
- A system of independent
suspension in which each wheel is located on a "knuckle" that
is connected by ball joints to an upper A arm and a lower A arm.
Usually, the lower A arms are longer. This system provides minimal
changes in track and camber when the suspension is under load,
as when going over bumps or in hard cornering.
The shaft that transmits
power from the transmission to the differential in a rear-drive
- Drag Coefficient
- A measure of the
aerodynamic sleekness of an object. Drag coefficient is signified
by "dc.: The lower the number, the greater the aerodynamic efficiency.
The higher the drag coefficient, the more a car's engine must
work to keep a given road speed. Also known as "CD" for coefficient
- The power-transmitting
components in a car, including clutch, gearbox (or automatic transmission),
driveshaft, universal joints, differential and axle shafts.
Dual Overhead Camshafts (DOHC)
- A DOHC engine has
two camshafts in each cylinder head; one camshaft actuates intake
valves and the other actuates exhaust valves. The camshafts act
directly on the valves, eliminating pushrods and rocker arms.
This reduced reciprocating mass of the valve train enables the
engine to build RPM more quickly. DOHC designs are typically high-performance,
four valve per cylinder engines. (A four valve per cylinder two
intake and two exhaust design helps the engine "breathe"
more freely for increased performance.)
- A device which absorbs
and measures the power derived by an internal combustion engine.
Auto Terms E
- Any solution that
conducts an electrical current, such as a mixture of sulfuric
acid and distilled water found in automotive batteries.
Fuel Injection System
- A system that injects
fuel into the engine and includes an electronic control unit to
time and meter the fuel flow.
- An ignition system
that uses transistors and other semiconductor devices as an electronic
switch to turn the primary current on and off.
- EPA Fuel
- Comparative mileage
figures generated from laboratory fuel-economy tests administered
by the federal Environmental Protection Agency (EPA) using simulated
weight and drag to approximate real driving conditions.
- An exhaust-emission
control system in which a portion of the exhaust gas is picked
up from the exhaust manifold and sent back to the intake manifold
t be reburned in the engine. Mixing exhaust gases with the fresh
air/fuel mixture lowers the combustion temperature and reduces
the formation of oxides of nitrogen in the exhaust.
- Exhaust Manifold
- The network of passages
that gathers the exhaust gases from the various exhaust ports
and routes them toward the catalyst, the muffler and the exhaust
- In used vehicles:
the combination of original standard equipment and production
options that make up the equipment of a used vehicle. May also
be referred to as "base" equipment.
- Fifth Wheel
- Load supporting
plate mounted to the frame of a vehicle. Pivot mounted, it contains
provision for accepting and holding the kingpin of a trailer,
providing a flexible connection between the tractor and the
trailer. Center of the fifth wheel should always be located
ahead of the centerline of the rear axle.
- Final Drive
- A fluid coupling
consists of two fan-like impellers in a sealed, oil-filled housing.
The input "fan" churns the oil, and the churning oil, in turn,
twirls the output "fan." Such a coupling allows some speed difference
between its input and output shafts. The automatic transmission's
torque converter is based on the fluid coupling principle.
- Four Wheel
- On a vehicle equipped
with Four-Wheel Anti-Lock Brakes, all four wheels are equipped
with speed sensors. When these sensors determine that the wheels
are decelerating so rapidly that lockup may occur, the Electro-Hydraulic
Control Unit (EHCU) is activated. The EHCU then modulates the
brake pressure in the appropriate brake lines by means of the
solenoid-operated valves. This is intended to prevent wheel
lockup and help the vehicle maintain directional stability during
potentially hazardous braking situations
- Four Wheel
- In a Four Wheel
Drive system, a secondary transmission assembly, called a transfer
case, is driven from the main transmission. The transfer case
distributes power to both axles to drive all four wheels. It
is the heart of the Four-Wheel Drive system. Four-Wheel Drive
can be full-time, in which power is delivered to both axles
at all times or part-time, where the driver selects two or four
wheel drive. Four wheel drive is often combined with independent
suspension systems and off-road type tires to enhance driveability
on rough, off-road terrain, or on-road driveability in unfavorable
- Four Wheel
- A type of suspension
in which all wheels are mounted to separate suspension members
with no rigid axle connecting them. Therefore a disturbance
affecting one wheel has no effect on the opposite wheel. Four
wheel independent suspension reduces the un-sprung weight, improves
ride and handling over rough surfaces and permits room for a
- A drive system
where the engine and transaxle components apply the driving
force to the front wheels rather than the rear wheels. Benefits
of Front-Wheel drive include: Maximized passenger space. Enhanced
cargo area. excellent drive traction; particularly on wet or
slippery surfaces, since the drive is through the front wheels,
which carry a heavier load.
- Fuel Injection
- A method of delivering
fuel under pressure into an engine's combustion chamber. Fuel
injection systems can be single-point, multi-point, etc.. Replaces
- Fuel Injection,
- A computer-controlled
method of delivering fuel under pressure. The computer monitors
signals from coolant temperatures, manifold vacuum, exhaust
oxygen sensor, and engine cranking sensor. It "tells" the injectors
to release and adjust the fuel to yield an air/fuel mixture
assuring engine operation well matched with emission requirements,
optimum fuel economy and overall vehicle performance.
- Fuel Pump
- A mechanical or
electrical device that draws fuel from the fuel tank and delivers
it to the carburetor or injectors