Definitions of automotive terms as used on this site.

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10W30 An SAE classification for oil with an equivalent viscosity of 10 when cold (zero Celsius) and 30 when hot (100 Celsius.) (see also viscosity and SAE)

2-wheel alignment Wheel alignment, where measuring devices are only attached to the front wheels rather than all four, as in a four-wheel alignment. This is normally less expensive than four-wheel alignment and adequate under certain circumstances. For instance when the rear alignment is known good. (see also our Suspension Repair Category.)

4-wheel alignment Wheel alignment, where measuring devices are attached to all four wheels rather than just the front, as in a two-wheel alignment. This has the added advantage of correcting the rear as well as front alignment and insuring that tracking is correct on the vehicle. (see also our Suspension Repair Category. )

4WD An acronym meaning Four Wheel Drive. An arrangement where the front and rear wheels can be linked to the transmission and used to propel the vehicle. (see also FWD and RWD)

5W30 An SAE classification for oil with an equivalent viscosity of 5 when cold (zero Celsius) and 30 when hot (100 Celsius.) (see also viscosity and SAE)

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A/S tire Stands for all season, a tire that can be used in snow as well as on the highway, but less aggressive than an M/S designation.

A/T tire Stands for all terrain, a tire that can be used in mud and snow as well as on the highway, more aggressive than an M/S designation.

AALA An acronym meaning American Automobile Labeling Act. A little known law, requiring vehicles sold in the United States to be labeled as to the percentage of US/Canadian content and the Country of manufacture. This information should be provided, upon request, by new vehicle dealerships in the United States.

Actuator A device used to perform a mechanical action and is operated by electricity, vacuum or fluid pressure. Actuators are often used to direct air from air conditioning systems in the dash.

Aftermarket part A part not supplied as original equipment on a vehicle, rather built by a third party. A part that is not supplied by the original manufacturer of a vehicle. (See also OEM part)

AGCO An acronym standing for Altazan's Garage COmpany; A Good COmpany

Air bag Another name for the Supplemental Inflatable Restraint (SIR) system. A combination of computer controlled inflatable devices that help cushion the occupants of the vehicle in a collision. (See also SIR)

Alignment Attachment of measuring devices to the vehicle’s wheels in order to measure and correct their positioning to the proper specifications. This can be done on the front wheels only, in a two-wheel alignment or all four wheels, in a four-wheel alignment. (See also 4-wheel alignment) and our Suspension Repair Category.

Antifreeze A chemical, often comprised of ethylene glycol or propylene glycol which is combined with water and add to the engine to prevent freezing. It also contains additives to prevent corrosion and raise the point of the mixture. (see also coolant.)

API An acronym meaning American Petroleum Institute. A body that among other things, rates oil and lubricants and assigns a classification that producers can voluntarily display on products that meet the specifications. A rating beginning with “S” is for gasoline engine classification. SN is the highest rating at the time of publication. Ratings starting with “C” would pertain to diesel engines. (see also SAE)

Aspect ratio The ratio of width to sidewall height of the tire. For instance a 235/75R16 tires is 75% as tall as it is wide. For a calculator to demonstrate aspect ratio see our Michelin Tire Category.

ASTM An acronym meaning American Society for Testing and Materials. An organization that provides standards for testing of a multitude of products and services. As related to automotive, particularly standards for engine coolant.

ATF An acronym meaning Automatic Transmission Fluid. It does not denote a specific fluid rather a general term. (See also Dexron and Mercon)

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Back probe Using a thin metal device (made for the purpose) to connect with the contacts in an electrical connector. The probe can be connected to different measuring devices used to monitor a signal in the circuit. Back probing is far superior to piercing the insulation or probing the connection area, which can result in damage.

BCM An acronym meaning Brake Control Module. The computer that controls the anti-lock brake system, also know as the Electronic Brake Control Module or EBCM. See our section on Brake Service.

Belt slap A derogatory term for simply replacing a timing belt on a high milage engine, ignoring the water pump, seals and other components which also often fail around the same milage. Please see our Detailed Topic All About Timing Belts for more details.

Bleeding Term which describes the process of removing trapped air from fluid. Often refers to brake bleeding or cooling system bleeding.

Bottoming When a suspension travels to the maximum limit of it’s downward design. When jounce bumpers contact their mating surface. (See also jounce and rebound)

Brake job An obsolete and improper term. Often used to describe replacing certain brake components, with no regard to whether they are needed or will address the client’s problem.

Brake master cylinder A hydraulic pump attached to the brake pedal. On pedal application it supplies hydraulic pressure into the system to apply the brakes.

Brake shudder A condition where the steering wheel moves side to side when braking and quits when the brakes are released. Feels similar to improper wheel balance except braking brings it on rather than driving a certain speed.

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C V Boot An acronym meaning Constant Velocity Boot. The flexible cover that protects the C V Joint by holding lubricant in and sealing contaminants out. Often used on front wheel drive and independent suspension rear wheel drive vehicles. (see also C V Joint)

C V Joint An acronym meaning Constant Velocity Joint. A type of coupling that allows power to be transmitted to a wheel at a wide array of angles. Often used on front wheel drive and independent suspension rear wheel drive vehicles. (see also FWD and RWD)

Cabin filter A filter on the intake side of the air conditioner blower that protects the evaporator core from dirt build up. Not all vehicles are equipped with cabin filters.

Camber The angle formed by a line drawn through the vertical center of a wheel/tire and true vertical. See also included angle and SAI

Certified used vehicle A marketing term for a late model, used vehicle that normally has an extended warranty tacked on to the price. These may come from all the same places that any used vehicles come from (e.g., auctions, trade ins, repossessions, etc.) They should be viewed with the exact same cautions as any other used vehicle.

Check engine light Another name for the Malfunction Indicator Light (MIL.) An indicator to the driver that a fault has occurred in the computer management system See our section on Engine Diagnostics. (See also MIL)

Clunker A derogatory term for any vehicle that is not still in the new car dealer’s inventory; A vehicle on which the salesperson has already been paid their commission. For instance, a “state of the art machine” becomes a clunker as soon as the sale is passed.

Clutch master cylinder A hydraulic pump attached to the clutch pedal. On pedal application it supplies hydraulic pressure into the system to apply the clutch. (See also slave cylinder)

Clutch slave cylinder A hydraulic cylinder that receives pressure from the master cylinder when pressure is applied to the pedal. The hydraulic pressure is converted into movement that releases the clutch. (See also clutch master cylinder)

Condenser A heat exchanger, normally located in front of the engine radiator. The condenser is used to convert hot gaseous refrigerant to cooler liquid refrigerant. This is accomplished by allowing air flow to remove the heat from the refrigerant.

Constantly variable transmission A type of automatic transmission that uses a belt to transmit power rather than gears. By varying the size of the drive pulleys the ratio is constantly varied and continuously delivered to the drive axles.

Coolant A mixture of anti-freeze and water used to cool the engine. (See also Antifreeze)

COP An acronym meaning coil on plug. An ignition system design where the ignition coil mounts directly to the spark plug and is fired by a low voltage signal.

Cost The initial amount paid, plus other expenses involved, divided by how long the product or service last. (See also price and The Difference In Price and Cost in our AGCO Philosophy Category)

Counterfeit parts Cheap substitute parts, often substandard, copied from OEM parts and represented to be OEM parts. Often imported from countries with no enforcement of counterfeiting laws. (See also OEM)

Crank When the starter motor causes the engine to turn in an effort to start.

Curb weight The full weight of a vehicle, with all standard equipment and a full tank of fuel, but without passengers.

CVT An acronym meaning Constantly Variable Transmission. (See Constantly variable transmission)

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Dealership An organization that has purchased the rights to sell a certain line of new vehicles. The agreement also normally requires them to perform warranty work on those vehicles. Dealerships often operate an auto repair shop and a parts store as part of their operation.

Detonation A rattling, pinging type noise, normally experienced on acceleration and under load. Left unattended engine damage can result. For more information see our Detailed Auto Topics Valve clatter, spark knock, pinging and pre-ignition. (see also spark knock, pinging and labor knock)

Dexron A type of automatic transmission fluid, widely used by General Motors and several other manufacturers, until recent years. Often mispronounced as dex-tron, there is no “T” in the name. Actual pronunciation is dex ron. (see also Mercon and ATF)

Dog tracking When the front and rear wheels do not track in the same path causing the vehicle body to appear to travel in an angled path to forward motion. Often the result of mis-aligned suspension, body or frame components.

DOT An acronym meaning Department Of Transportation. A governmental body that regulates some safety aspects of vehicles.

DTC An acronym meaning Diagnostic Trouble Code. A combination of numbers and letters, stored by the vehicle’s computers to give an indication of the circuit in which a fault may be exist. See our section on Engine Diagnostics and our Vehicle Questions Category for What do OBDII codes actually mean?

Dynamic balance Balancing a wheel in both dimensions, side to side and from one face to the other. Because wheels have width, they need balance not only from side to side but also from one side of the width to the other. Dynamic imbalance normally manifest as a wobble from side to side, at higher speeds. (see also wheel balance, static balance and wheel weight)

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ECM An acronym meaning Electronic Control Module. ECM could describe any computer on the vehicle but is often used interchangeably with PCM or power control module. (see also PCM)

EGR An acronym meaning Exhaust Gas Recycle. A system that cools the fuel air mixture in the engine, under certain conditions to help prevent pre-ignition. For more information see our Detailed Auto Topics Valve clatter, spark knock, pinging and pre-ignition of. (see also spark knock, detonation, pinging and labor knock)

Emergency brake An outdated term to describe the vehicle parking brake. In early days before vehicle hydraulic brake systems employed redundant design, mechanical emergency brakes were used. In the case of brake failure they could be used to stop the vehicle. (see also parking brake)

Engine Flush A service often marketed to clean the engine crankcase. Very seldom actually needed and usually no more effective than more frequent oil changes. (see also wallet flush)

EP An acronym meaning Extreme Pressure. A lubricant that has been designed to withstand very heavy loading, often used in rear differentials. (see also viscosity)

EPDM An acronym for Ethylene Propylene Diene Monomer, a very tough and flexible material, often used in construction of high-quality automotive belts and hoses. EPDM is much tougher than neoprene and requires a different method of checking for wear, on belts. For more information on EPDM belts, please see our Detailed Topic, Symptoms of A Bad Serpentine Belt and EPDM Belts.

Evaporator A heat exchanger, normally located in the passenger compartment. Used to remove heat from the passenger area, by absorption, using a low pressure gaseous refrigerant.

Expansion valve A mechanical device used to regulate the flow of liquid refrigerant into the evaporator core, thus helping to regulate the temperature of the core. (see also orifice tube and evaporator core)

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Flash update An update to or replacement of computer software on the vehicle’s computer(s) performed by a repair shop. Vehicles that support flash updates can be reprogrammed, using the proper type of scan tool and without replacement of parts. Replacement computers must also be flashed after installation.

Flat rate A method of billing, where a predetermined amount of time is charged rather the actual time a repair takes to complete. The time billed is often taken from a guide, known as a flat-rate guide. Express your opinion on flat rate pricing.

Flat rate tech A technician paid a predetermined amount of time for a job, rather the actual time it takes to complete. The time paid is often taken from a guide, known as a flat-rate guide. Express your opinion on flat rate pay methods.

Frame A vehicle construction technique where the body is bolted to a separate frame. The frame provides the rigidity and an attachment points for suspension components, similar to the skeleton of the human body. Very few cars but several trucks and SUV’s use frame type construction. (see also uni-body)

FWD An acronym meaning Front Wheel Drive. An arrangement where the front wheels are linked to the transmission and are used to propel the vehicle. (see also RWD)

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Gas filled shock absorber A shock absorber containing a charge of low pressure gas that helps keep the hydraulic fluid from foaming.

Gov-lock differential A locking type rear differential that uses centrifugal force to move a counter-weight and lock the rear wheel together under wheel slip conditions. Widely used in trucks, by General Motors, starting around 1973. (see also limited slip and posi-traction)

Gray market A vehicle or part imported through other than the official distribution network. Such vehicles may not meet safety, emission or lighting standards of the country into which they are imported.

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Head gasket Material used to seal, coolant, oil and compression in the area where the cylinder head(s) attach to the engine block.

Hot tank A metal tank, filled with a heated caustic solution and used to clean cast iron and other ferrous materials. The hot tank is effective at removing grease, dirt and some rust. It is not appropriate for aluminum or soft metals and will cause damage to them. For this and for environmental reasons, the use of hot tubs has diminished greatly in recent years. (see also jet wash)

HSLA An acronym meaning high strength low allow, referring to a type of steel used in automobile construction.

HSS An acronym meaning high strength steel, referring to a type of steel used in automobile construction.

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Included angle The angle formed by a combination of camber and steering axis inclination (SAI). (see also camber and SAI)

Independent repair shop An organization designed to service vehicles and owned independently, as opposed to a franchise or mass-merchandiser.

Injector flush The practice of cleaning fuel injectors with a chemical and some sort of pressurized device. Often sold as necessary or as maintenance but only beneficial when there is an actual problem. (see also wallet flushes)

Inner tie rod The flexible pivot that connects the steering mechanism to the outer tie rod, usually by a threaded connection. Steering-box type systems usually use a tie rod similar to the outer connecting each with a threaded sleeve. Rack and pinion systems normally use a rod as below. Threaded to the rack on one end and with threads to provide adjustment and attachment to the outer tie rod on the other end. (see also outer tie rod and rack and pinion)

IPC An acronym meaning Instrument Panel Cluster. The computer that operates the dash instruments and often the security system and overall communications between computers on the system.

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Jalopy A slang term for an old vehicle, particularly one in disrepair

Jet wash A cabinet fitted with high pressure nozzles and a rotating floor, used to clean automotive components. Hot soapy water is blasted against the components as they rotate inside the cabinet. The jet wash is very effective for cleaning aluminum, iron and plastic components. The cleaning solution may be recycled, is non-toxic, and the jet wash is considered environmentally friendlier than other cleaning methods. (see also hot tank)

Jounce Downward travel of the suspension; pushing the vehicle down in the front or rear to settle the suspension, as in alignment. (see also rebound)

Jounce bumper Flexible devices, often rubber, located at points on the suspension where contact might otherwise occur between components that move on jounce and rebound. Flexible cushions that slip over the shaft of McPherson struts and dampen bottoming. (see also jounce and rebound)

Jump timing A malfunction where a timing chain, belt or sprocket breaks or slips and the camshaft is no longer properly synchronized with the crankshaft.

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KAM An acronym meaning Keep Alive Memory. Battery powered backup memory used by the various control modules on a vehicle.

Keyless entry system Systems designed to unlock vehicles without the use of a key. Often a remote transmitter with a push button, but numeric key pads have also been employed. Very often linked to the onboard security system and can be used to activate personalize radio and seat position settings as well.

Killed When an engine unexpectedly quits running and the ignition is still on. (i.e., The engine killed)

Kink A type or degree of bend in a frame resulting in a fold of metal with a radius of 3MM or less. Generally accepted as the point at which a frame can no longer be structurally repaired.

KOEO An acronym meaning Key On Engine Off. One state in which pre-OBDII vehicles could be tested. (see also OBDII and KOER)

KOER An acronym meaning Key On Engine Run. One state in which pre-OBDII vehicles could be tested. (see also OBDII and KOEO)

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Labor knock A rattling, pinging type noise, normally experienced on acceleration and under load. Left unattended engine damage can result. For more information see our Detailed Auto Topics Valve clatter, spark knock, pinging and pre-ignition. (see also spark knock, detonation and pinging)

Lean A condition where the amount air to fuel is more than the ideal 14.7 to 1. Too much air or too little fuel in the ratio. Can result in loss of power, high cylinder head temperature and misfires.

Lease A method of purchasing a vehicle, where equity in the vehicle is traded for a lower monthly payment. A lease is similar to rental, except the person leasing is general committed to the term and conditions of the lease. Please see our Detailed Topic, Problems With Automobile Leasing for additional information.

Limited slip A type of differential that attempts to apply equal force to both drive axles. This is usually accomplished by linking them together through a series of clutches and drive plates that only slip when necessary. (see Posi-traction)

Lock-up (torque converter) A clutch in the torque converter that “locks” the input to the output at a specified time. This prevents further slippage of the torque converter and improves fuel mileage. Lock-up clutches are normally controlled by the computer through solenoids and hydraulic pressure. (see also Torque converter)

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M/S tire Stands for mud and snow, a tire that can be used in mud and snow as well as on the highway.

Maintenance Service performed and parts replaced in the hope of preventing other, more expensive parts from failing. For instance coolant is replaced in the hope of preventing corrosion damage to radiators, heater cores and engines. The cost of the coolant is a fraction of the cost of the repairs it can prevent. Read more on maintenance.

McPherson strut A suspension component that contains a shock absorber but also supports the weight of the vehicle through a spring or torsion bar. See also shock absorber

Menu pricing A method of assigning a price to a specific service decided on in advance. A name is assigned to the service with no regard to whether it is needed or will address a problem. Menu prices are often set at a level geared to get the client in the shop and never intended as what will be charged. (see also spiking the job, brake job and tune up) and how much is a brake job and how much is a transmission.

Mercon A brand name for a type of automatic transmission fluid, widely used by Ford Motor Company. The name is also used, with a suffix, for several other specialty automatic transmission fluids, such as Mercon Premium, Mercon LV, Mercon V, etc. (see also Mercon V, Mercon SP, Dexron and ATF)

Mercon SP A brand name for a type of specialized synthetic automatic transmission fluid, with additional additives, and used by Ford Motor Company in certain transmissions. Mercon SP may not be replaced with Mercon V, which would not meet the same specifications. (see also Mercon V, Dexron and ATF)

Mercon V A brand name for a type of synthetic automatic transmission fluid, with special additives and widely used by Ford Motor Company. Mercon V may not be replaced with Mercon, which would not meet the same specifications. (see also Mercon, Dexron and ATF)

Metal on metal The characteristic grinding noise made when the friction material wears off of brake shoes or pads and the metal backing scores the rotor or drum surface.

MIL An acronym meaning Malfunction Indicator Light. An indicator to the driver that a fault has occurred in the computer management system See our section on Engine Diagnostics. (see also Check Engine Light)

Multi viscosity In oil, the ability to change the resistance to flow over a range of temperatures. For example 5W30 is the SAE designation for an oil that can flow like a five-weight oil at low temperature (0 degrees Celsius) and like a thirty-weight oil at high temperature (100 degrees Celsius.) (see also viscosity)

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NEFR An acronym meaning Not Economically Feasible to Repair. A vehicle that has deteriorated to a state where repair would far exceed the value of the vehicle. A condition often brought on by following extended maintenance intervals. (see also our Detailed Topic entitled The Sad Truth)

Negative The smaller of the two tapered battery post on top mount batteries. Normally attached to ground and color coded black. (see also positive)

NHTSA An acronym meaning National Highway Traffic Safety Administration. A division of the Department of transportation that regulates automotive recalls and safety issues. See our Links Category for current recalls and more information.

NIST An acronym meaning National Institute for Standards and Technology. A national organization concerned with setting standards for automotive air-conditioning systems.

Normal service As defined by most manufacturers, should more properly be called ideal service. For example longer trips at highway speed with little stop and go driving. Under these conditions the normal service schedule is okay. (see also severe service and maintenance)

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OBD II An acronym meaning On Board Diagnostics II. This is a diagnostic standardization of fault codes and connections to the vehicle diagnostic system. Implementation began around 1994 and was implemented fully by 1996. (see also our Vehicle Questions Category for What do OBDII codes actually mean?)

Octane The word octane is often interchanged with octane rating. In reality octane is a hydrocarbon and octane rating is a point of pressure at which gasoline will spontaneously combust. This is important in an engine, because when fuel combust before the ignition ignites it, damage may occur. For more information see our Detailed Auto Topics Valve clatter, spark knock, pinging and pre-ignition of. (see also octane rating and posted octane rating)

Octane rating Octane rating refers to the ability of fuel to resist spontaneous combustion (pre-ignition.) Iso-octane has a rating of 100 (great resistance to spontaneous combustion) and n-heptane has a rating of 0 (little resistance to spontaneous combustion. Basically, fuel with a rating of 87 octane would have at minimum, the same spontaneous combustion point as a mixture of 87 percent iso-octane and 13 percent n-heptane. (see also octane and posted octane rating)

OEM An acronym meaning Original Equipment Manufacturer. For instance a part that is the same manufacturer as the original part that came on the vehicle may be called an OEM part. See also aftermarket part

Orifice tube A small fixed tube used to regulate the flow of liquid refrigerant through the evaporator core, thus helping to regulate the temperature of the core. (see also evaporator core and expansion valve)

Outer tie rod The flexible pivot that connects the steering arm to the remainder of the steering mechanism. Usually tapered and threaded at the connection with the steering arm and threaded to provide adjustment on the other end. Steering-box type systems usually use a similar rod on the inner side connecting each with a threaded sleeve. (see also inner tie rod)

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Parking brake A series of mechanical devices that use a pedal or lever and cables to apply front or rear brakes. So called because they are intended to hold the vehicle in place when parked. (see also emergency brake)

PCM An acronym meaning Power Control Module. The power control module is a computer that operates the engine and sometimes transmission of the vehicle. (see also ECM)

Phaser A variable camshaft sprocket, used to change the valve timing while the engine is running. Phasers are normally operated by oil pressure and controlled by the power control module. Solenoids may vary oil pressure supplied to the phaser and enable adjustment to camshaft timing.

Pinging A rattling, pinging type noise, normally experienced on acceleration and under load. Left unattended engine damage can result. For more information see our Detailed Auto Topics Valve clatter, spark knock, pinging and pre-ignition. (see also spark knock, detonation and labor knock)

Plug Short for spark plug. A replaceable component in the ignition system that provides the spark necessary for combustion.

Posi-traction A brand name for a type of limited slip differential that used clutches and springs to assist rear traction. The name is outdated today but is still often used to describe any limited slip differential. (see limited slip)

Positive The larger of the two tapered battery post on top mount batteries. Normally marked with a plus sign and color coded red. See also negative

Posted octane rating US octane ratings are assigned based on a combination of two testing methods. The results of the Research method and the Motor method are averaged for a posted octane rating. On the label below, R stands for research and M for motor methods. See also octane and octane rating

Price The initial amount paid for a product or service without regard to other expenses involved or how long the product or service last. See also The Difference In Price and Cost in our AGCO Philosophy Category. (see also Cost)

Program car A marketing term for a late model, low mileage used vehicle that is still under factory warranty. These may come from all the same places that any used vehicles come from (e.g., auctions, trade ins, repossessions, etc.) They should be viewed with the exact same cautions as any other used vehicle.

PSI An acronym meaning Pounds per Square Inch; a measure of pressure. Also expressed as PSIA meaning pounds per square inch absolute. PSI includes atmospheric pressure which is approximately 14.7 PSI at sea level. NOT the measure of tire pressure. (see also PSIG)

PSIG An acronym meaning Pounds per Square Inch Gauge; a measure of pressure that a gauge is likely to read. It does not include atmospheric pressure which is approximately 14.7 PSI at sea level. The pressure in a tire is expressed as PSIG. (see also PSI)

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Quad-driver A portion of the power control module (PCM) that receive inputs are sends outputs to other sensors and devices. Similar to the drivers on a home or office computer that control the printer and disk drives. Each quad-driver controls four functions.

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R12 The name of an air conditioning refrigerant also often referred to as Freon. Largely discontinued from automotive use by 1993.

R134A An automotive air conditioning refrigerant brought into use after the discontinuation of R12.

Rack and pinion steering A device that attaches the steering wheel to a small gear, known as the pinion. When the gear is rotated by turning the steering wheel, the pinion drives a long gear known as the rack. The rack moves at a 90 degree angle to the steering column. The ratio of the two gears multiplies the steering effort and redirects motion in the proper direction to turn the front wheels in the direction desired.

Rebound Upward travel of the suspension; suspension returning to normal position after jounce. (see also jounce)

Recall A mandatary correction of a defect in a vehicle, ordered by the National Highway Traffic Safety Administration (NHTSA.) Recalls are for defects that may affect public safety. For information on recalls look in our Links Category.

Refrigerant A gaseous compound used in the air conditioner system, normally R134A or in older vehicles R12.

Rich A condition where the amount of air to fuel is less than the ideal 14.7 to 1. Too much fuel or too little air and can result in fowled spark plugs, poor fuel mileage and dark smoke from the exhaust.

Rotation Moving front tires to the rear of the vehicle in an attempt to even out the wearing process. Often the left-front is placed on the left-rear and the right-front on the right-rear. Tires may also be crossed to the rear in many cases (e.g., left-front to right-rear and right-front to left-rear. Rotation does not require balance, which is a totally different process. (see also wheel balance)

RWD An acronym meaning Rear Wheel Drive. An arrangement where the rear wheels are linked to the transmission and are used to propel the vehicle. (see also FWD)

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SAE An acronym meaning Society of Automotive Engineers. One of the organizations that helps set automotive standards such as oil ratings, used in the United States.

SAI An acronym meaning Steering Axis Inclination. The angle formed by a line drawn through the upper and lower pivot points of the suspension and true vertical. (see also Included angle and camber)

Severe service As defined by most manufacturers is often the service most folks operate under. For instance, ANY of the following would be considered severe service. Most daily trips are less than five miles one way. Most driving is stop and go. High temperatures, above 90' F. Towing If ANY of these conditions describes your use, it is better to follow the severe service schedule. (see also normal service and maintenance)

Shimmy A condition where the steering wheel moves side to side when driving at certain speeds. Often a condition of improper wheel balance. (see also wheel balance, dynamic balance, static balance and wheel weight)

Shock absorber A hydraulic device that resist motion in the suspension of an automobile. They are designed with specific rates of dampening and these rates may vary with the amount of force applied and differ on jounce and rebound. (see also jounce, rebound, gas filled shock absorber and McPherson strut)

SIR An acronym meaning Supplemental Inflatable Restraint. A indicator to the driver that a fault has occurred in the air bag management system See our section on Engine Diagnostics. (see also air bag)

Solenoid In automotive terms a solenoid is an electromagnetic device used to convert electrical energy into physical movement. Widely used in a many applications from controlling the valves in an automatic transmission to moving the starter drive gear. An electrical coil is energized and draws a magnetic plunger in or out, depending on design. Movement of the plunger is used to open valves, move switches, make or break electrical connections.

Spark knock A rattling, pinging type noise, normally experienced on acceleration and under load. Left unattended engine damage can result. For more information see our Detailed Auto Topics Valve clatter, spark knock, pinging and pre-ignition. (see also detonation, pinging and labor knock)

Spark plug A replaceable component in the ignition system that provides the spark necessary for combustion.

Speed rating A testing method used to determine quality of a tire to resist centrifugal force. Tires are tested by spinning at increasing speed until they are destroyed. A heavier belted tire normally has a higher speed rating and is so noted on the tire sidewall with a letter designation. S = 112 mph T = 118 mph U = 124 mph H = 130 mph V = 149 mph Z = in excess of 149 mph W = 168 mph Y = 186 mph

Spiff A reward or monetary sum paid to a technician or service advisor in order to influence the sale of a specific product or service. For instance ten dollars for each transmission flush. Express your opinion on flat rate pricing. (see also wallet flushes)

Spiking the job I derogatory term, used to describe the practice of misleading a client, in order to get the vehicle in the shop and disable it. Often used with low-ball pricing. Once the vehicle is disabled, it is far less likely to be taken out of the shop, once the true price is revealed. (see also menu pricing)

Starter The electrically operated motor that causes the engine to rotate when the starter switch is activated.

Static balance Balancing a wheel in a single plane only (e.g., like a bubble balancer from days gone by) Because wheels have width, they need balance not only from side to side but also from one side of the width to the other. Static imbalance normally manifest as a bouncing vibration. (see also dynamic balance, wheel balance and wheel weight)

Swaptronics A derogatory term for an unskilled technician’s method of changing parts, especially electronic components hoping to solve a problem and rather than proper testing.

Synthetic oil A name that refers to certain properties possessed by an oil. Contrary to common belief, it does not specify what the oil is made of and some oils sold as synthetic are actually highly refined petroleum products. Also see our section on Oil, Lubricants and Gasoline for more.

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TCM An acronym meaning Transmission Control Module. Another name for the computer that controls the transmission. Sometimes transmission control is handled by the power control module, without a separate transmission computer see also PCM

Temporary battery end A terminal that clamps onto the end of a battery cable, as opposed to a proper factory crimp style terminal. Often causing high resistance and damage to the electrical components of the vehicle.

TIM An acronym meaning Technician Induced Malfunction; A derogatory term for an unskilled technician’s who causes further damage while testing or in an attempt to repair.

Top Tier Gasoline Six top automakers, Audi, BMW, General Motors, Honda, Toyota and Volkswagen felt the EPA minimum detergent standards were too low. These automakers established the Top Tier standard to address the problem. In order to meet Top Tier, gasoline producers must meet several standards for reduced deposits and detergency in all of their grades. The list of Top Tier providers may serve as a guide to motorist. Some of the companies in our area that meet Top Tier are: Chevron Texaco Conoco Phillips 66 Shell

Torque Converter On automatic transmissions, the coupling device between the engine and transmission. A fluid-filled turbine that allow the engine to continue to run while the vehicle is stopped. As engine speed increases, torque is transmitted to the transmission. Torque converters serve much the same function as the clutch on a manual transmission.

TPMS An acronym meaning Tire Pressure Monitoring System. A system that monitors tire air pressure and warns of a low tire. Mandated by 2008 but also used on several vehicles much earlier.

Transfer case An apparatus that allows power to be transmitted from the transmission to the front and/or rear wheels. (see also FWD, RWD and 4WD)

Transmission flush Using a machine to run transmission fluid through a transmission, in an attempt to clean it. The filter is not cleaned and sometimes a universal fluid is used, rather than that specified by the manufacturer. (see also wallet flushes) and the section on proper transmission service.

TSB An acronym meaning Technical Service Bulletin. This is information, released by the manufacturer of a vehicle, subsequent to production. Often it points to an improvement or change to resolve a problem. It is NOT a recall and does not obligate the manufacturer beyond the normal vehicle warranty terms (see also recall)

Tune up An obsolete and improper term. Often used to describe replacing certain ignition components, with no regard to whether they are needed or will address the client’s problem.

Type F An automatic transmission fluid used by Ford Motor Company several years ago. Largely out of current use except in classic vehicles. (see also Dexron, Mercon, ATF)

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U-joint An abbreviation for universal joint. A cross with four caps using roller bearings to allow the drive-shaft to operate at a limited range of angles.

U.S. built vehicle According to the American Automobile Labeling Act (AALA) A vehicle assembled in the United States, using at least 75% components that are from the United States or Canada. (see also AALA)

Uni-body A vehicle construction technique where structural body panels are welded together to support the vehicle with no separate frame used. Most cars built today are uni-body construction. (see also frame

Unidirectional tread A tire tread pattern where the grooves follow a single direction. Theoretically better at dissipating water from under the tread while in motion. Care must be taken to insure the tire is mounted properly and most have an arrow showing proper rotation.

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Vacuum brake booster A chamber with a diaphragm dividing the two halves. Vacuum is present on both sides until the brake is applied. On application, atmospheric pressure enters the pedal side, forcing the diaphragm towards the master cylinder. This applies the brakes and greatly reduces brake pedal effort.

Valve body A component of the automatic transmission where valves, solenoids, check balls, passage ways and springs are used to control shifting and other functions of the transmission.

Valve clatter A rattling, pinging type noise, normally experienced on acceleration and under load. Left unattended engine damage can result. For more information see our Detailed Auto Topics Valve clatter, spark knock, pinging and pre-ignition. (see also detonation, pinging and labor knock)

Variable-ratio power steering A system that uses a solenoid to control the amount of boost the power steering receives, based on speed and steering input. At low speed the boost is raised for ease of steering. At speed the boost is reduce for firmer control.

VIN An acronym meaning Vehicle Identification number. A unique 17 digit number that identifies the vehicle and gives specific information. For instance the first digit reveals the country of origin. The eighth digit represents the engine option. The tenth digit is the year model and the final seven digits are the serial number of the vehicle.

Viscosity In oil, the resistance to flow at a given temperature and often expressed on a numeric scale. On the scale established by the Society of Automotive Engineers (SAE) the lower the number, the less resistance to flow. For instance an oil rated 10 oil flows more quickly than an oil rated 90, at the same temperature. There are also other scales such as the one established by International Standards Organization (ISO).

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Wallet flush Any of a number of services, of questionable worth, often marketed by shops, merely to increase their profit. (see also fuel injection flush, engine flush and transmission flush)

Wheel balance Placing wheel weights on the outside and inside of a wheel to allow for variations in the weight of the wheel/tire assembly. A properly balanced wheel will have only one weight per-side of the wheel and will not require re-balance under normal service, for the life of the tire. (see also rotation)

Wheel offset The distance from the mounting face of a wheel to the actual centerline of the wheel. A wheel with a mount face at the actual center would have zero offset. If the mounting surface is inboard (toward vehicle center) of the wheel centerline, the offset is negative. If the mounting surface in outboard (away from vehicle center) of the centerline, the offset is positive.

Wheel weight Small pieces of metal (usually lead alloy) clipped or adhesively attached to a wheel in order to achieve balance of the wheel/tire assembly. Wheel weights come in a variety of shapes to fit different style wheels as well as several different weight amount. (see also wheel balance)

White box A derogatory term for cheap aftermarket parts, often sold in a white box with no name. (see also aftermarket part and counterfeit part)

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X-frame A vehicle frame that has an X-member welded between the frame rails. (see also X-member)

X-member An X-shaped member welded between the frame rails to strengthen a vehicle frame.

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Y-pipe A Y-shaped pipe that connect the two exhaust banks of a V-style engine into one single pipe. Often used to save money routing both banks through a single muffler and catalytic converter.

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Zerk fitting The small fitting used to attach a hydraulic grease gun to a component in order to apply lubrication (e.g., a ball joint or tie rod.)