This glossary will define and explain specific Subaru terminology as well as additional features unique to Subaru vehicles.
A-Pillar Front body posts that support the roof, windshield and front doors
Adjustable Steering Column or Wheel This feature permits the driver to tilt the steering column or wheel up or down to the most comfortable position. Some columns also have a telescoping feature allowing the wheel to be moved in and out.
Adjustable Suspension Some performance suspensions feature controls (usually air-powered) that permit the driver to make adjustments while the vehicle is in motion, used to accommodate vehicle performance, road conditions, and/or passenger and cargo loads.
Aerodynamic Drag or Air Resistance The action of airflow, passing over and around an object, which tends to create friction and slow the object. Body designs are affected by this friction and designers try to create more streamlined shapes to reduce it. When drag or resistance is lowered, less power is needed to maintain a given speed, and in some cases, vehicle stability is increased.
Air Bag Supplemental Restraint System (SRS) The Supplemental Restraint System (SRS) (air bags) affords the driver and front passenger additional protection in a frontal or (when equipped with front seat side-impact air bags) a side impact collision. These systems provide supplemental protection only, and seatbelts must be worn in order to avoid injuries to out-of-position occupants upon bag deployment and to provide the best combined protection in a serious accident. Children should always be properly restrained in the rear seat.
Air Cleaner A filter mounted in the engine's air induction system to prevent dust, dirt and other airborne objects from being drawn into the engine.
Air Dam A device mounted below the bumper assembly to reduce aerodynamic lift by channeling the airflow around the vehicle, rather than under it. It also aids in more efficient cooling by reducing air turbulence under the vehicle, promoting better airflow through the radiator.
Airfoil A wing-like aerodynamic device, usually mounted on the rear of the body, designed to enhance traction by increasing downward air pressure on the vehicle. This device also improves stability but often at the cost of increased drag. (see spoiler)
Ratio of air to fuel in the combustion chamber, measured by weight or mass.
Air Scoop An opening in the body used to direct outside air to a certain part of the vehicle such as the brakes, engine air intake or radiator.
Air Shocks Shock absorbers that can be bolstered by air from a pimp. Used to adjust a vehicle's suspension height to accommodate cargo/passenger loads and road conditions. Also called "load levelling".
Alignment Usually refers to wheel alignment relative to caster, camber, toe-in and ride height. Term may also be used where frame or unit body damage has occurred.
Alloy Metals combined to form unique characteristics as in nickel-chrome or aluminum alloys.
Alloy Wheels A term usually used to describe any non- steel road wheel. Most alloy wheels are fabricated of aluminum alloy or magnesium alloy and are noted for their styling and light weight.
All-Wheel Drive This drive configuration engages all four wheels at all times to drive the vehicle.
Alternator Sometimes referred to as a "generator", it converts mechanical energy from an engine-driven belt or gear into electrical energy to charge the vehicle's battery and operate the electrical system when the engine is running.
Anti-Dive A designed-in front and rear suspension characteristic that converts braking forces in the suspension links into a vertical force that reduces the tendency of the front and/or rear of the car to drop or dive during hard braking.
Anti-Freeze Engine cooling liquid (ethylene glycol) mixed with water and added to the engine's cooling system to prevent freezing in cold weather. Most brands also inhibit rust and other deposits which could reduce cooling efficiency, as well as raise the boiling point temperature of the engine coolant.
Anti-Lock Braking System (ABS) A system which senses and helps prevent wheel lockup in emergency or severe braking situations. ABS automatically pulses or pumps the brakes to help prevent loss of vehicle to a safe stop on slippery or wet road surfaces.
Automatic Climate Control A thermostatically controlled heating and air conditioning system which automatically balances heated and cooled air to help maintain a preset temperature.
Automatic Locking Retractor (ALR) Seatbelt configuration that can be locked in place by fully extending the belt and then feeding the belt back into its retractor to the desired position. Useful in securing a child safety seat. (see emergency locking retractor)
Automatic Transmission A power-transmitting component which permits changing of forward and reverse gears without a manually operated clutch. A 4-speed electronic controlled automatic transmission (4EAT) is available on all Subaru models. The 4EAT transmission uses a computer to determine the optimum shift points for all driving conditions.
Axle A metal shaft on which a wheel revolves or a shaft revolves with the wheel. It can also be a solid beam that connects two wheels of a vehicle and in some cases, transmit power or motion to the drive wheel. Often refers to a front or rear pair of wheels, regardless of whether they are connected by a solid axle.
B-Pillar The side or door support that connects the rocker panel and floor plan with the roof, providing support for the roof and doors.
Baffle A plate or other restrictive device used to change or direct the flow of gases or liquids to prevent surging and cavitation or to reduce sound. In vehicles, baffles are found in fuel tanks, crankcases, mufflers, radiators and intake systems.
Balance Shaft Metal shaft designed to reduce or cancel engine vibration. The shafts rotate in the opposite direction of the engine crankshaft.
Ball Joints Flexible devices which are used in steering and suspension systems to allow for motion that changes direction at a given point.
Battery A device which converts chemical energy into electrical energy. The typical battery for vehicles produces power for cranking the engine and initial ignition. It also supplies current for other electrical systems in the vehicle and when current demand exceeds the output of the alternator. Low maintenance batteries need fluid added on occasion. Maintenance-free batteries seldom, if ever, need fluid and may have a sealed top.
Bead A feature of tires, consisting of a band of reinforced steel or nylon covered with rubber that seals the inside edge of each sidewall to the wheel rim.
Belt (Engine) A reinforced band of rubber or composite material used to drive certain engine components from the crankshaft. Belts can also be used for engine timing and for various components such as the power steering pump, alternator, water pump or air conditioner compressor.
Belt (Tire) A band of material (usually fiberglass or steel) that reinforces the tire. It runs around the circumference in several layers (plies) with its fibers at 90 deg (radial) or at an angle (bias), and strengthens the tread and sidewall.
Blow-Off Valve A device to prevent pressure from building up in the Inter-Cooler.
Body-On-Frame Construction Type of traditional vehicle construction where the body structure is attached to a separate frame.
Boost A term applying to the amount of pressure above normal atmospheric pressure, which is supplied to the air intake of the manifold from a turbocharger or supercharger. Boost is measured in PSI. (pounds per square inch)
Bore And Stroke Usually used together, these are engine measurement. Bore is the cylinder diameter; stroke is the distance the piston travels. These two determine the cylinder displacement or volume.
Boxer Engine Engine type that features cylinder heads at a 180 deg angle to each other, recognized for high performance in a compact layout with a lower centre of gravity for improved handling. The engine provides extremely low vibration. (see horizontally opposed engine)
Brake Booster A device actuated by air, vacuum or hydraulic pressure that multiples the driver's pedal effort on the brake system, reducing the effort normally required to stop a vehicle. Such systems are usually referred to as power-assisted brakes or power brakes.
Brake Fade A condition resulting from repeated brake applications in which heat build-up causes a temporary reduction in brake effectiveness.
Brake Horsepower Also called "bhp", this is a dynamometer measurement taken by attaching a mechanical brake to the engine crankshaft to measure the engine's maximum power output.
Brake Linings Replaceable friction-generating material secured to the brake shoes of drum brakes, which contact the wheel drum to slow or stop a vehicle.
Brake Master Cylinder A component containing a movable piston actuated by the brake pedal. The piston uses hydraulic pressure to push fluid through the lines to the wheel calipers or cylinders, which force the brake pads or linings against the disc or drum to slow or stop the vehicle.
Brake Proportioning Valve A valve that adjusts the braking force to the rear wheels based on rear to front weight transfer. When braking, it is designed to help prevent premature rear wheel lockup by metering the hydraulic action of the brake system.
Brake Shoe Arc-shaped lining holder in a drum brake system used to force the lining against the rotating drum when braking.
Break-in Period, either in time or mileage, during which new moving parts, such as engine components, become seated as rough edges are gradually reduced and mating surfaces aligned.
C-Pillar The rear pillars that support the rear window and the rear window and the rear portion of a vehicle's roof.
CAFE Acronym for Corporate Average Fuel Economy, a mileage figure determined by an average of fuel consumption for all models produced by the manufacturer and then modified by the actual sales in each EPA category. The minimum requirement is a government standard. A manufacturer can be fined for noncompliance.
Caliper A disc brake component that straddles the disc and houses the hydraulic cylinder, pistons, brake pads and bleeder assemblies. The caliper forces the brake pads against the disc to slow or stop the vehicle.
Cam Profile Geometric shape of the camshaft lobes that determines when and how far the valves open and close. (see camshaft)
Camber The inward or outward tilt of the top of the tire as viewed from the front.
Camshaft A shaft in the engine driven by gears, belts or a chain from the crankshaft. It has a series of lobes for timing the opening and closing of intake and exhaust valves. The profile of each lobe determines the time or "duration" the valve is open as well the amount the valve moves, known as "lift".
Caster The forward or backward tilting of a wheel's steering axis as viewed from the side. If the load is forward of the point of wheel contact, the caster angle is considered negative.
Catalytic Converter A stainless steel canister fitted to the exhaust system that uses platinum, palladium and/or rhodium as a catalyst to produce a chemical reaction in the exhaust. It converts hydrocarbons and carbon monoxide into water vapor and carbon dioxide, reducing harmful engine emissions.
Center Differential A differential used in some all wheel drive (AWD) and four wheel drive (4WD) systems to distribute power between the front and rear axles.
Center Of Gravity Center point of a vehicle's mass used to calculate a variety of handling and vehicle attitude parameters. A lower center of gravity will tend to promote more stability.
Chassis The vehicle frame or underbody to which all parts, including the engine, drivetrain, suspension and brakes attach. Also, considered to be the vehicle without its body, accessories and trim.
Clutch A device used to engage and disengage the engine from the transmission. Manual clutches use a clutch pedal to force a clutch plate to move, releasing pressure from a friction-faced disc. This allows the transmission to stop spinning while the engine continues to run, allowing the gears to be shifted without clashing. When the pedal is released, the flow of engine power (motion) is restored to the drivetrain.
CO Chemical symbol for carbon monoxide, a highly toxic, colourless, odourless gas produced as a by-product of combustion in a gasoline engine.
Coil Spring Spiral-wound resilient metal component that can be compressed or extended without permanent deformation. Normally used in suspensions to provide a smoother ride and increased control, it also helps to support the weight of the vehicle's body.
Collapsible Steering Column A steering column engineered to collapse on impact, helping to prevent serious injury. Column is fitted with a special collar so it telescopes or is made of material designed to crush upon an impact of a given weight factor.
Combustion Chamber The space at the top of the cylinder where the air/fuel mixture is burned.
Compression Ratio Volume of the cylinder and combustion chamber when the piston is at the bottom of its travel divided by the volume when the piston is at the top of its travel. This represents the amount that the fuel/air mixture is compressed for combustion.
Compressor (Air Conditioning) The device in an air conditioning system that pumps vaporized refrigerant out of the evaporator, compressors it and sends it to the condenser.
Condenser (Air Conditioning) A system component used to remove heat by allowing air to pass over coils and convecting heated air to the atmosphere.
Constant Velocity Joint (CV Joint) An improved version of the universal joint that can operate without the vibrations caused by applying torque at an angle, as on the drive shafts of front-wheel drive vehicles.
Contact Patch The area of a vehicle's tire tread in contact with the road surface.
Coolant The mixture of water and antifreeze that absorbs heat from the engine and transfers it to the air as it passes through the radiator. This process keeps the engine operating at its optimum temperature range, preventing damage from excessive heat.
Coolant Recovery System Container coupled to the radiator that stores coolant that overflows due to the heat expansion, and returns it to the radiator after it cools.
Cooling System The system designed to absorb excess engine heat; it includes the coolant radiator, fan, water pump, thermostat, hoses and engine water jackets.
Cowl Part of the vehicle body between the engine compartment and windsheild; it houses the bulkhead panel and usually the air intake for the heater, defroster and air conditioner.
Crankcase The engine component enclosing the engine crankshaft. In most engines, the oil pan and lower part of the cylinder block form the crankcase.
Crankshaft The main shaft of the engine that transfers the reciprocating linear motion of the pistons into rotary motion to drive the transmission and ultimately the road wheels. It is named because it was the shaft where early engine hand cranks were inserted before starter motors were developed.
Crossmember One of the several lateral ladder-like elements joining the frame saide rails to add overall strength and stability.
Crumple Zones Areas of the vehicle that are designed to crush upon impact and absorb the energy of a collision while maintaining the structural integrity of the passenger compartment.
Curb Weight The standard measured weight of a vehicle with all standard equipment and fluids, including oil, lubricants, coolant and a full tank of gasoline.
Cylinder Block Basic engine component that contains the cylinders and upper crankcase it is the core of the engine. It is usually a casting to which all other engine parts are attached.
Cylinder Head Bolted to the cylinder block, this part of the engine seals the cylinders and contains the combustion chambers. It also holds the spark plugs and valves in most engines.
D-Check This self-diagnosis mode of the engine control module is used by dealer technicians to check and detect faults in the entire MPI system.
D-Pillar The roof-supporting member at the extreme rear of station wagons, some sedans and sport utility vehicles.
Damper See shock absorber
Decklid A relatively horizontal hinged door or panel providing access to the trunk or luggage compartment.
Detonation Spontaneous combustion of the compressed air/fuel mixture in a cylinder before the spark plug fires, resulting in knock or ping, which increases mechanical and thermal stresses on the engine.
Differential Driving-axle gear assembly located in a center housing between the driving wheels on rear-wheel drive vehicles, or as apart of the transaxle on front-wheel-drive vehicles. It transmits power to the wheels while allowing each wheel to rotate at different speeds, if necessary, as when turning a corner.
Direct Ignition System (DIS) A system which applies ignition voltage to each spark plug via individual coil units, rather than using a single coil, secondary ignition wires and a distributor.
Directional Stability Ability of a vehicle to maintain a true course of travel under the effects of crosswinds and road conditions.
Disc Brake Brake type employing a flat rotor or disc attached to the wheel, and a stationary caliper which contains the friction pads and piston(s). Very efficient, especially at high temperatures.
Displacement The primary measure of an engine's size, displacement is the total volume within the engine's cylinders that is swept by the moving pistons in their stroke. It is usually expressed in liters, cubic centimeters (cc) or cubic inches.
Distributor Ignition system component, usually driven by thecamsgaft. Distributes electrical power to fire each spark plug in the proper sequence.
Distributorless Ignition A system that replaces a traditional distributor, cap and rotor with maintenance-free multiple coil units. This system provides more accurate ignition control for greater efficiency and reliabilty.
Double (or Dual) Overhead Camshaft (DOHC) A DOHC engine has two camshafts in each cylinder head: one to operate the intake valves and another to operate the exhaust valves.
Drag Coefficient (CD) A number used in calculating the aerodynamic value of a vehicle. The lower the number, the more efficiently the body slips through the air. Drag coefficient is a big factor in fuel efficiency, wind noise and vehicle stability.
Drive Shaft (Propeller Shaft) A shaft with universal joints at each end linking the transmission to the differential and transferring power to the same.
Drivetrain A term referring to the power-transmitting components of a motor vehicle, including engine, clutch transmission, driveshaft, U-joints, differential, axles and wheels.
Dual Diagonal Braking System A brake system that is split to increase braking stability and prevent complete failure in case one or more components lose hydraulic capability. System splits with one front and the opposite-side rear wheel in each part of the system.
Dynamometer A device which measures and absorbs the power of an engine. Used to measure brake horsepower, torque and other engine performance capabilities and during emission testing in state inspections.
Electronically Controlled Automatic Transmission Microcomputer-controlled automatic transmission that selects shift characteristics based on data from electronic sensors which measure speed, engine load and environment.
Electronically Tunes Radio (ETR) AM/FM stereo radio that accurately tunes in a desired station and provides drift-free reception and a digital display of station selected.
Emergency Locking Retractor (ELR) An integral part of the seatbelt system that permits the belt's free movement unless sudden deceleration is encountered, at which time the belt locks securely.
Engine Control Module (ECM) A microprocessor capable of receiving many input signals and directing the operation of the fuel injection and ignition systems. To maintain maximum efficiency, the ECM has the ability to learn and age to compensate for normal wear and tear in the engine components. Self-diagnosis aids in serviceability and a limp-home mode maintains driveability in the event of component failure. (see also:self-diagnosis and limp-home mode)
EPA Fuel Economy Fuel economy rating determined by tests administered by the Environmental Protection Agency (EPA) under laboratory conditions, using simulated weights and drag to create "real" driving conditions.
Ergonomics The integration of man and machine used in cars to determine the design and positioning of controls, switches, instruments seats, pedals and steering wheel so they are properly located for easy, comfortable and logical operation.
Exhaust Emission Controls Systems designed to limit harmful gases in an engine's exhaust. Grouped in two categories: 1) those designed to reduce or eliminate formation of harmful pollutants in the engine itself and, 2) those designed to destroy or other wise alter pollutants after they are formed. Emission controls generally are found in the crankcase, gas tank, air cleaner, exhaust manifolds and exhaust systems.
Exhaust Gas Recirculation (EGR) An exhaust emission control system in which exhaust gas is recirculated from the exhaust manifold to the intake manifold to reduce or eliminate the formation of nitrous oxide (N2O).
Exhaust Manifold An assembly of tubes, usually cast iron, that directs exhaust gases from the cylinder head exhaust ports and routes them to the exhaust system.
Exhaust Pipe Long heavy-gauge steel tube routing exhaust gases from the exhaust manifold to the catalytic converter, muffler and tail pipe.
Fast Idle Control Device (FICD) Controls engine idle speed by compensating for additional loads from air conditioner or automatic transmission. Also provides smooth idle when engine is cold.
Final Drive Ratio Ratio between the transmission output shaft and the drive-wheel axle shaft. Ratio compares the rotation of the differential pinion gear to the rotation of the differential (ring gear). Low numerical ratios generally offer greater top-speed fuel efficiency. High ratios deliver more torque and are preferred to towing.
Firing Order The sequence in which the high-voltage ignition charge is delivered to the spark plugs to begin the combustion process.
4-Channel/4-Sensor ABS An advanced method of monitoring and controlling each wheel's brakes used on certain Subaru models. The fourth channel of a Subaru system permits the use of dual diagonal braking in combination with ABS technology for increased safety.
Four-Valve Cylinder Head A cylinder head that has two intake valves and two exhaust valves per cylinder for better breathing, increased efficiency and higher maximum rpm.
Four-Wheel Drive A drive system where both the front and rear wheels can receive power through a trasnfer case. Full-time four-wheel drive delivers power to the front and rear axles all the time. Part-time four-wheel drive allows the driver to select either two-wheel or four-wheel drive modes to meet road conditions (four wheel drive is typically used on off-road sport utility-type vehicles).
Four-Wheel Independent Suspension Type of suspension where each wheel is independently sprung without solid - beam axles. This permits each wheel to react to road irregularities independently of the others. Generally, improves ride, handling and control.
Frame Separate structural underpining of a vehicle which supports the engine chassis components and body and is, in turn, supported by the wheels.
Front-Wheel Drive (FWD) Front-wheel drive (FWD) uses a transaxle to transmit power to the vehicle's front wheels, thus "pulling" the vehicle and benefiting from the engine's weight being over the drive wheels.
Fuel Injection Fuel system using an electric pump and injector nozzles instead of a carburetor to meter fuel to the engine. Three main types include: 1) Sequential multi-port, uses one injector for each cylinder which injects fuel at the exact time it is needed into each intake port. 2) Multi-port, uses one injector for each cylinder which injects fuel directly into each intake port. 3) Single-point throttle body, uses one injector which meters fuel into the intake manifold upstream from the intake valves. Electrically operated mechanical fuel injection uses the engine's microprocessor to control injectors for precise balancing of the air/fuel mixture.
Fuel Pump Electrical or mechanical pump that draws fuel from the tank and delivers it to the carburetor or fuel injector(s).
Fuel System The total system that routes fuel to the engine and includes the tank, fuel lines, evaporative system fuel filter(s), pump and either carburetor or fuel injector(s).
Full-Floating Axle An axle design that permits the axle housing to ear the weight of the vehicle rather than the axle and the housing.
Full-Time All-Wheel Drive (AWD) See All-Wheel Drive.
Fuse A device containing thin wire or metal foil that that melts or separates (at a predetermined amperage level) if excessive electrical current flows through it, as with an electrical short. The fuse protects a given circuit if there is excessive current draw.
Gas-pressurized Shock Absorber Shock absorber featuring a nitrogen gas chamber in addition to the traditional air/oil chamber. This type of shock provides more stable damping under a variety of conditions.
Gasket Thin, soft material (usually cork, cardboard, rubber or soft metal) used between two surfaces or components to ensure a good seal.
GCWR (Gross Combination Weight Rating) Term used for both trucks and cars where trailer hauling is concerned. This is based on the combined Gross Vehicle Weight Rating of both the towing and towed vehicles. (Note: Some manufacturers use the total curb weight plus the weight of the driver in place of the towing vehicle's GVWR to establish the GCWR for the towing vehicle.)
Gearbox Component in the drivetrain that contains a system of gears for multiplying torque and changing the vehicle's direction. A gearbox is used with either a clutch (manual transmission) or a torque converter (automatic transmission) to provide the required changes.
Gears Toothed wheels which, when meshed, drive each other. By using gears of different diameters a torque multiplying or reduction effect takes place, so that each gear rotates at a different speed.
GVWR (Gross Vehicle Weight Rating) The maximum carrying capacity for a given vehicle, including the weight of the vehicle and its contents. It is measured by adding the total curb weight of the vehicle and its contents. It is measured by adding the total curb weight of a vehicle plus optional equipment, passengers and payload. This becomes the maximum carrying capability of the vehicle, over which it should never be operated.
Halfshaft (axle shaft) Rotating shaft, normally used in pairs that transmits power from the differential to a driving wheel. These are found on front-wheel-drive vehicles, all-wheel drive vehicles or rear-wheel drive vehicles with independent rear suspension.
Halogen Headlights Headlamp bulb with a quartz or glass envelope and tungsten element filled with inert gas containing iodineor another of the five halogen gases. These lamps produce as much as 25 percent more lighting power per watt of electrical power than the standard sealed-beam headlights and typically emit a whiter light.
Headers A term used to describe tubular exhaust manifolds. Traditionally, domestic engines used inefficient cast iron manifolds to reduce cost. In addition to their light weight, tubular steel headers have higher flowrates and a greater ability to dissipate heat.
Heated Intake Anti-pollution component that helps vaporize fuel supplied to a cold engine. An air cleaner with the thermostat is connected via a hot air pipe to a stove-like hot air warmer on the exhaust manifold. When the engine is cold, the thermostat closes a damper, routing warm air from the exterior of the exhaust manifold or catalytic converter to the carburetor or air intake manifold. As the engine warms, the thermostat gradually cuts down on the warm air routing and opens to a regular engine compartment. Or ducted outside air.
Hemispherical Combustion Chamber Originally referred to as "Hemi-Head", this is a dome-shaped combustion chamber with valves at a 45 deg angle to the piston top. This shape is known to increase engine power output considerably.
High Altitude Compensation Device installed on the engine that allows it to perform efficiently and economically at high elevations where the oxygen content of the ambient air is reduced. Device(s) usually works through the engine's microprocessor.
Hitch Ball A ball-like pivot mounted on a tow vehicle that connects the trailer to the tow vehicle. This permits the trailer to turn during cornering. Hitch balls are available in a range of sizes and ratings.
Horizontally-Opposed Engine Engine type that features cylinder heads at 180 deg angles to each other. All Subaru engines are horizontally-opposed. (see boxer engine)
A unit measure of power, such as engine output, equal to the rate of 33,000 lb. -ft. per minute used to rate engine power out put. One horsepower equals 550 lb. -ft. per second (the power needed to lift 550 pounds one foot off the ground in one second).
HVAC Abbreviation for Heating Ventilating and Air Conditioning used to describe a vehicle's interior air-flow system.
Hydraulic Control Unit (HCU) Device which provides control of the fluid direction in pressurized circuits such as anti-lock braking system (ABS).
Hydrocarbon (HC) Automotive emission caused by combustion composed of hydrogen and carbon.
Idle Speed Control (ISC) A device (solenoid) controlled by the onboard computer to provide a constant idle speed under varying conditions.
Ignition System System that provides the spark to ignite the air/fuel mixture in the combustion chamber. Consists of battery, alternator, high-voltage coil, distributor (some systems don't use a distributor), ignition switch, spark plugs and wiring. Electronic ignitions operate at a somewhat higher voltage.
Independent Suspension Type of suspension in which a pair of wheels, either front or rear, is suspended in such a manner that the response of one wheel to a bump is independent and has no effect on the opposite wheel. (see four-wheel independent suspension)
Induction System Component system made up of engine intake valves, intake ports, intake manifold and a carburetor or fuel injection system. This system delivers the air/fuel mixture to the cylinders.
Intake Manifold Network of passages, usually cast aluminum, through which air/fuel mixture flows from the carburetor or throttle valve to the intake ports of the cylinder head.
Heat exchanger found on turbocharged or supercharged engines. It cools the engine intake air between stages of compression, providing a denser air mix.
Jounce Any wheel movement that compresses the vehicle's suspension. The opposite of rebound.
Kickdown A downshift in an automatic transmission caused by depressing the throttle.
Sound made by loose or worn mechanical parts in an engine. Also used to describe pre-ignition detonation during acceleration when using inappropriate low-octane fuel or when an engine is improperly adjusted.
Knock Sensor Device used to sense detonation or ping in an engine. Unit sends a signal to the engine microprocessor to retard ignition timing until the ping or detonation is eliminated.
Laminated Windshield Windshield using safety glass comprised of a clear plastic laminate between two pieces of glass, so that on impact, the shattered glass does not splinter, reducing sharp edges which can cause serious injury.
Lead-free (Unleaded) Gasoline Gasoline without tetraethyl lead or other lead components as additives to increase octane rating. Most unleaded gasoline today uses ethanol to increase the octane rating, which reduces detonation or pinging.
Light-emitting Diode (LED) Solid-state device that can emit light without a filament has an extremely long life and requires very low power. Used in some center-mounted stop lamps.
Limited-slip Differential Differential that can direct power away from a slipping wheel to a wheel with better traction. It I very effective on slippery roads.
Limp-Home Mode The engine control module (ECM) and transmission control module (TCM) monitor component inputs/outputs during self-diagnosis. If certain components fail to respond or respond with a signal that is out of the normal operating range, the ECM or TCM will automatically compensate for the error and activate the fail safe function to maintain driveability until it can be serviced. Refer to the individual service manuals for a list of the components that are covered. (see also: self-diagnosis)
Liquid Crystal Display (LCD) Device used in digital displays such as clocks, ETR radios, gauges and trip computers.
Lockup The point at which a wheel starts to skid during braking. Maximum braking effectiveness occurs when a wheel is on the verge of lockup.
Lockup Torque Converter Component that contains a special clutch forming a solid connection between the engine output shaft and the transmission at a preset speed, reducing energy losses and increasing efficiency.
Lubricating System Closed system that delivers oil to the moving parts of the engine. The system includes the oil pump, oil pan, coolers, tubing, filters and passages within the engine block.
Macpherson Strut Suspension design known for being efficient and compact. Macpherson struts provide a coil spring and shock strut mounted on the same axis, such that the spring surrounds the upper portion of the shock absorber.
Main Bearings Large bearings in the engine that support the crankshaft.
Manifold Absolute Pressure (MAP) Sensor Electronic sensor that monitors the precise amount of load that is placed on the engine and sends a signal to an onboard computer that will supply the correct amount of fuel.
Muffler Attached to the exhaust pipe, this canister, fitted with baffles and insulation, permits the exhaust gases to expand and cool, while reducing exhaust noise.
Multi-plate Transfer (MPT) Clutch Clutch used on electronically controlled 4-speed automatic transmission-equipped All-Wheel-Drive Subaru models which controls the amount of front-to-rear power split. It is operated by the Transmission Control Module.
Multi-port Fuel Injection (MFI) Fuel system with one injector at each intake port that injects the correct amount of fuel directly into the cylinder intake port to provide precise fuel delivery. (see fuel injection)
Noise Vibration and Harshness (NVH) One of the many quantifiable aspects of ride quality. Major factors in vehicle NVH are: tire selection, body rigidity, suspension bushings and insulation.
On-board Diagnostics Version II (OBD-II) Designed to reduce service costs and problems, this government-mandated system uses industry-wide code conventions for engine diagnostics. All OBD-II vehicles regardless of manufacture can be diagnosed using a single monitoring device.
Odometer Instrument for measuring elapsed vehicle mileage. Odometers are not legally reversible. However, trip odometers can be manually reset to measure miles between gas fill-ups or trips.
Oil Pumps A pump driven by the engine that delivers oil in the lubricating system to the moving parts of the engine.
Overdrive The one or two highest gears in some manual or 4-speed automatic transmissions employed to reduce engine speed and contribute to fuel efficiency. An overdrive gear by definition rotates at a higher rpm than the engine crankshaft.
Overhead Cam (OHC) A camshaft located above the cylinder head(s) in an engine. This design shortens the movement of the valve train and permits more responsive valve action, often leading to greater engine-power output. A single overhead cam installed in a head is referred to as SOHC. A double overhead cam, one for the intake valves and one for the exhaust valves, is referred to as DOHC.
Overhead Valve Engine (OHV) An engine that employs rocker arms actuated by pushrods and camshaft in engine block to open and close intake and exhaust valves.
Oversteer A condition during turning in which the slip angle of the rear tires is larger than that of the front tires, such that the driver needs to reduce steering input to maintain the same turning radius. Rear-wheel-drive vehicles tend to oversteer.
Oxides of Nitrogen (N2O) Chemical compound produced in engines by a combination of high pressure and high heat within the combustion chamber which causes oxygen and nitrogen to unite into nitrous oxide.
Oxygen Sensors (O2) The O2 sensor monitors the oxygen content of the engine's exhaust gases. From this information, the engine control module (ECM) adjusts the air/fuel ratio to maintain efficiency.
Part-time Four Wheel Drive A four-wheel-drive (4WD) system that normally operates in a two-wheel-drive mode. Drivers can engage 4WD simply by pressing a switch or engaging a lever. Vehicles with "shift on the fly" can select 4WD while moving.
Ping Common name given to the noise generated in an engine that is not properly maintained or uses an inappropriately low grade of fuel. Also known as detonation or knock.
Pinion A name for a gear with a small number of teeth designed to mesh with a larger gear called a ring gear or toothed rack. Principally used for rack-and-pinion steering systems and differentials.
Piston Cylindrical engine component that fits into each cylinder of the engine block and is attached to the crankshaft by a connecting rod. Pistons move up and down in the cylinder, compressing the air/fuel mixture on the rising stroke and transmitting the force of combustion to the crankshaft on the downward stroke, causing the engine to run.
Plenium Chamber A chamber located between the throttle body and runner of the intake manifold used to distribute the intake charge evenly.
Plies On tires, layers or belts of fabric, fiberglass, steel or other flexible fibers that reinforce the tire body.
Polyvinyl Chloride (PVP) A plastic that can be used in conjunction with automotive paint to help prevent chipping and scratching. Generally used on body areas on Subaru models that are susceptible to stone damage, including the front edge of the hood and the lower body panels. (see stone guard coating)
Pound-Feet (LB.-FT.) The unit measurement of torque. One pound-foot is equal to the twisting force produced when a pound force is applied to the end of a one-foot-long lever.
Power Brakes Brakes using a vacuum or hydraulic booster to multiply the driver's effort as the steering wheel is turned, reducing effort.
Rack-and-Pinion Steering Steering system that has a "pinion" gear at the end of the steering column . This meshes with a toothed bar called a "rack" which moves left or right when the steering wheel is turned.
Radial-Ply Tires Tire design where the reinforcing layers run from bead to bead, across the tread, improving ride and wear characteristics over bias ply designs.
Radiator Heat transfer component of the cooling system. Receives hot engine coolant, transfers heat to the atmosphere and returns cooled fluid to the engine.
Read Memory Check Instrument panel message from the onboard computer which allows the technician to check the microprocessor for intermittent circuit faults.
Rear-Wheel Drive (RWD) Automotive drivetrain where the rear wheels are used to propel of drive the vehicle.
Recirculating-Ball Steering Steering design using a recirculating ball bearing on a worm shaft to transmit turning forces to a "sector" gear that moves a Pitman arm and connecting rod to turn the front wheels.
Redline Maximum recommended speed, expressed in revolutions per minute (RPM) for an engine.
Usually indicated by a red area or tachometer.
Refrigerant A liquefied gas used in automotive air conditioners to cool the air in the interior of a vehicle. It absorbs heat as it changes from liquid to gas in an evaporator. This heat is released as it changes back to a liquid in a condenser. Most manufacturers now use the CFC-Free refrigerant R-134a, because it does not harm the ozone layer.
Resonator An auxiliary muffler used with the main muffler to further reduce exhaust noise and "tune" the sound.
Ride Height A measurement between the ground and a fixed reference point on a vehicle's body.
Road Holding A vehicle's ability to grip the pavement. Technically referred to as a "lateral acceleration". Measured in g, with 1g equal to the force of gravity on an object.
Roll Rotation of a car's body about a longitudinal axis. Also called "sway" or "lean".
Rolling Resistance The motion-resisting force that exists as soon as a wheel begins to turn. Such resistance is related to tire pressure, road surface, vehicle weight, tire construction and temperature. Tires with lower rolling resistance have a positive effect on the fuel economy.
SAE (Society Of Automotive Engineers) Professional association that sets most auto industry standards for testing, measuring and design.
Sedan Any fixed-roof car with at least 33 cubic feet of rear-seat interior volume (per SAE Standard J1100)
Self-Diagnosis The self-diagnosis systems detects and indicates faults in various inputs and outputs of the engine control module using the check engine light to indicate the occurrence of a fault prior to the OBD-II system. The self-diagnosis function has four modes (U-check, D-check, read memory and clear memory) for storing, alerting and servicing problems. (see also: u-check, d-check and read memeory)
Semi-Elliptical Spring A leaf spring that is shaped like part of an ellipse or arc-slightly curved.
Sequential Multi-Port Fuel Injection Fuel system which injects gasoline into each intake port at the exact time it is needed. (see fuel injection)
Shock Absorber (Damper) Device used primarily to damp (absorb) suspension movement, usually by forcing oil through small internal passages in a tubular housing. Used for controlling motion and absorbing some of the energy jolts and bumps from road irregularities before they can reach the body.
Short Circuit Condition in an electrical system that allows the current to take a "short path" instead of following the designated path. This usually burns out related circuits and blows fuses.
Single Overhead Camshaft (SOHC) See overhead camshaft.
Skidpad A large area of smooth, flat pavement used for road handling tests.
Sludge Oxidized petroleum products mixed with an emulsion of oil, water and dirt that can clog oil systems and block engine lubrication.
SOA Subaru Of America, Inc., with headquarters in Cherry Hill, N.J.
Spark Plug Ignition component installed in each combustion chamber of gasoline-powered engines. Provides a gap across which high voltage jumps, creating a spark which ignites the air/fuel mixture.
Speed Sensor Device that converts the speed of an object into electrical signals for processing by an on board computer. Used to determine speed of engines, shafts and wheels, as with ABS.
Spoiler Body component attached to a vehicle, usually on the rear decklid, to induce a downward force to the vehicle. Term gets its name because it "spoils" the airflow over the body and also adds to vehicle styling (see airfoil)
Stabilizer bar Component linking both sides of a suspension (front, rear or both) to reduce body roll and improve overall handling characteristics, particularly when cornering. Device is usually a torsion bar mounted with rubber bushings to allow it to move freely.
Starter Motor A high-torque electric motor powered by the car's battery used to engage the flywheel and crank the engine until it starts to run on its own.
Steering Arm The steering arm, sometimes referred to as a Pitman arm, attached to the steering knuckle in a recirculating-ball (or worm and sector) steering system. The arm turns the knuckle and steering rod, which turns the wheels.
Steering Ratio The ratio of gearing within a steering system is related to the driver's steering effort.
Steering System System of components that permits a driver to guide a vehicle by changing directions on demand. The system includes a steering wheel, steering couple, steering gear, linkages, front wheel supports and any power assists, hydraulic or electric pumps.
Stone Guard Coating A heavy, relisient type of PVC coating applied under paint in areas exposed to constant impact from road debris. On Subaru models, it its used under the front bumper, at the extreme lower edges of fenders and sill areas and on the leading edge of the hood. (see polyvinyl chloride)
Strut Support member of a suspension system. Most struts incorporate both a coil spring and a shock absorber, through the term often refers only to the shock absorber portion.
Subframe A short frame usually front-mounted to the bodies of unit body-constructed vehicles. It is used to support the engine, transmission and suspension rather than having these components mounted directly to the unit body. Any substructure used to attach a system of components (such as a suspension assembly) to the frame or chassis of a car may be called a subframe.
Sub-woofer An audio system speaker or speaker/enclosure system designed to reproduce only bass frequencies. Generally used only below 80Hz.
Tachometer Instrument that measures the speed at which the engine crankshaft is rotating to indicate engine speed at which the engine crankshaft is rotating to indicate engine speed in revolutions per minute (RPM). (see redline)
Thermostat In a car engine, a heat sensitive valve used in the cooling system that opens or closes at preset temperatures. This helps regulate the flow of engine coolant between the cylinder block and the radiator to maintain optimum engine operating temperature and to ensure a more rapid warm-up.
Throttle-Body Fuel Injection (TBI) Fuel system that meters gasoline into the intake manifold upstream from the intake valves. (see fuel injection)
Timing The synchronized action of valves opening and closing or of the ignition system firing the spark plugs, both relative to the position of the crankshaft or pistons.
Tire Ratings Standardized measured and projected performance ratings for tires, including load capacity, traction, quality, top speed capacity, temperature resistance, treadwear expectancy and maximum acceptable pressure.
Toe-In Term used to describe the amount the front wheels are turned in, or toward one another. Most vehicles specify a slight amount of toe-in to keep the front wheels parallel when offsetting forces or suspension movement tend to spread them apart.
Tongue Weight Amount of trailer weight pressuring down on and supported by the hitch ball of the tow vehicle.
Torque Term used to describe a twisted or rotating force, such as the rotating force generated by the crankshaft or applied tro a bolt while tightening it. (see pound-feet)
Torque Converter A fluid coupling used to transfer power from the engine to the automatic transmission, it serves to multiply torque and cushion the flow of power.
Torque Steer In a front-wheel-drive vehicle that has unequal-length half shafts (axle shafts or driveshafts), the tendency for the car to pull to either side under acceleration. It is caused by the imbalance of torque between the different-length halfshafts.
Torsion Bar A type of spring that is normally a long straight bar anchored to the frame at one end and to the suspension at the other and offering resilience through a twisting motion. Torsion bars are easily adjusted and can affect wheel alignment.
Track Distance between the centers of tire pairs, front or rear.
Traction Control System (TCS) An electronic control system that helps prevent wheelspin by detecting when a driven wheel is about to lose traction and then reducing engine power and/or applying the appropriate brakes to prevent it. The majority of TCS systems on the market are "Low Speed" systems that use either brake or engine control at speeds of up to 25 mph. Sophisticated "All Speed" hybrid systems combine engine and brake control to help maintain traction control is a component of the Subaru VDC System.
Transaxle A drivetrain component where the clutch, gearbox, final drive and differential are all combined into one transmission-axle unit that connects directly to the driveshafts. Transaxles are used in many front-wheel-drive vehicles due to their compactness.
Transmission Drivetrain component that changes speed and power by using different gear ratios or other torque-altering mechanisms between the engine and drive wheels.
Transmission Control Module (TCM) The TCM microprocessor controls the automatic transmission's shift patterns, torque converter lock-up, power and economy modes and AWD operation by responding to inputs from a variety of sensors and switches. Self-diagnosis aids in serviceability, and a limp-home mode maintains driveability in the event of component failure. (see also: self-diagnosis and limp-home mode)
Transverse-Mounted Engine Most commonly found in front-wheel-drive vehicles, the installation of an engine in a "sideways" manner such as that the crankshaft runs across the car rather than front-to-back, in order to allow a larger passenger compartment.
Turbocharger A device used to pump air under pressure to engine cylinders in order to boost the normal air charge. This allows the engine to burn fuel more efficiently to produce additional power.
Turbochargers, unlike superchargers, require hot exhaust gases to drive the turbine pump. This results in a certain lag in the turbocharger effect at lower engine speeds, when the exhaust pressure is weak.
Tweeter An audio system speaker designed to reproduce only high frequencies.
Understeer Condition in which the slip angle of the front tires is greater than that of the rear. A car is said to "understeer" when it resists turning and tends to go straight, requiring the driver to turn the steering wheel further to maintain the same curve. Front-wheel-drive cars tend to understeer.
Universal Child Safety Seat System The UCSSS is a uniform anchorage (attachment) system for all new motor vehicles and child safety seats. The new system will greatly simplify child safety seat installation and will protect children by keeping seats more secure in vehicles.
Unit Body Body construction that incorporates the chassis floorplan and body structure as one unit, rather than requiring a full-length frame to provide structural strength or support for mechanical components.
Universal Joint (U-Joint) In the power train or a rear-wheel-drive vehicle, a jointed connection in the driveshaft that permits the driving angle to change. (see constant velocity joint for front-wheel-drive vehicles)
Unsprung Weight All weight in a vehicle that is not supported by the suspensions system. This is normally the weight of components such as brakes, hubs, wheels and tires.
User Check (U-Check) Method of informing the driver that a fault has occurred in a computer-controlled system. User check illuminates a warning lamp on the instrument panel.
Vacuum Advance Device that automatically adjusts the spark timing based on intake manifold air pressure. Vacuum advance offers the added spark adjustment needed for optimum fuel economy when the engine is only operating at part throttle.
Valve Engine part that allows fuel and air in or out the combustion chambers or any device that can stop and start the flow of fluid or a gas through a tube, pipe or other part.
Valves Per Cylinder The breathing capacity of an engine - more valves per cylinder typically produce better breathing, resulting in greater engine efficiency and a higher rpm redline.
Vapor Lock Occurs in high-heat conditions in which the fuel boils in the fuel system, forming vapor bubbles that slow or stop the flow of fuel to the carburetor or fuel-injection system.
Variable Torque Distribution (VTD) AWD System A Subaru AWD system that uses an electronically controlled hydraulic transfer clutch working in conjunction with a planetary gear-type center differential to control the power distribution between the front and rear wheels. Used in conjunction with the VDC system.
Vehicle Dynamics Control (VDC) System A Subaru system for vehicle dynamics control that monitors vehicle stabilityand reacts to minimize understeer, oversteer and drift conditions helping to maintain vehicle direction stability on all road surfaces. Using a yaw rate sensor to measure rotation movement of the vehicle, VDC can sense impending loss control at either the front or the rear of the vehicle and momentarily apply the brake(s) on one or more wheels to help restore stability, something that even skilled drivers cannot do. The VDC system also incorporates an all speed Traction Control System (TCS) to reduce wheel spin.
Viscosity Term refers to the resistance of any liquid to flow or its "thickness". Oil with its high viscosity is very thick and flows slowly, especially when cold.
Viscous Coupling A power transfer method employing a series of clutch plates surrounded by a silicon fluid that rapidly becomes very viscous when it is heated to a certain temperature. The friction caused by a slipping wheel or wheels, which makes one axle or drive shaft rotate faster than the other, causes the fluid to heat up, becoming thick and "locking" the differential. As a result, both axles or drive shafts (and thus both front and rear wheels or both rear wheels) turn at the same speed, sending the power to the wheel or wheels with the best traction. This is an integral part of the center and rear differentials on certain Subaru All-Wheel-Drive models.
Voltage Regulator Device that controls the voltage in a vehicle's charging system and prevents it from exceeding predetermined limits. It also helps maintain a constant system voltage.
Water Pump Device consisting of a driven pulley and an impeller, usually mounted at the front of the engine and driven by belt, pulley or gears off the front of the cranksaft, in order to circulate coolant through the engine's cooling system.
Weatherband Radio In addition to the standard AM and FM bands, a wetherband radio allows the listener to tune into any weatherband frequencies in the area for up-to-the-minute weather report.
Weight Distribution Manner in which total vehicle weight is distributed over each axle and tire of a vehicle. Proper distribution of vehicle and equipment weight is essential to the suspension's useful life and vehicle stability. Usually expressed as a percentage ratio front-to-rear such as 60/40.
Wheelbase The distance from the center of the vehicle's front wheels to the center of its rear wheels.
Wheel Cylinder Hydraulic cylinder used on brakes systems consisting of metal pistons and rubber seals. In drum brakes, a small spring-loaded hydraulic cylinder with two actuating piston forces the brake shoes against the drum when activated by the brake master cylinder. In disc brake system with a full floating caliper design, the cylinder pushes against the inner brake pad clamping the pads together against the brake disc.
Wheel Size The diameter and width of a road wheel to which a tire is mounted.
Wiring Harness A group of color-coded wires (bundled together for easier management and routing) that carry power to the various electrical compartments or systems.
Yaw Condition that puts a vehicle at an angle along a vertical axis to its forward line of travel; swinging from left to right. Similar to a ship's side-to-side motion in rough water.