Mobile Mechanic & Car Repair Glossary

A

ABS (Anti-Lock Braking System)

A system that keeps the wheels from locking up during hard braking so you can keep steering. If the ABS warning light is on, normal braking usually still works but the anti-lock function may not. Get it checked soon, and treat a red brake light as more urgent. Read moreSee also: Brake Fluid, Wheel Bearing, Diagnostic Trouble Code (DTC)

AC Recharge

Adding refrigerant to the air conditioning system so it blows cold again. If the system is low, it usually has a leak somewhere, so a good service includes checking for leaks rather than only topping up. Read moreSee also: Refrigerant

ADAS Calibration

Re-aiming the cameras and sensors used by driver-assistance features such as lane keeping and automatic emergency braking. It is often needed after a windshield replacement, alignment or collision repair. It usually requires special targets and a level floor, so it is generally a shop job. Read moreSee also: Wheel Alignment, Bay

Aftermarket Parts

Parts made by companies other than the carmaker to fit your vehicle. Quality ranges from equal to or better than original down to low-grade, and prices vary to match. Using them does not by itself void your car's warranty in the US. Read moreSee also: OEM Parts, Magnuson-Moss Warranty Act

Alternator

The engine-driven generator that charges the battery and powers the electrics while the engine runs. A failing alternator can cause dim lights, a battery warning light, or a car that dies while driving even with a newer battery. Read moreSee also: Starter, Serpentine Belt, Battery Load Test

ASE Certification

A credential from the National Institute for Automotive Service Excellence (ASE), earned by passing tests in specific areas such as brakes or electrical and having hands-on work experience. Certifications must be renewed periodically. It shows tested knowledge; it is not a business license and not a promise about any single repair. Read moreSee also: ASE Master Technician, Mobile Mechanic

ASE Master Technician

A mechanic who has passed a full group of ASE tests in a category, such as automobile and light truck, and met the work-experience requirement. It shows broad tested knowledge across many systems. Read moreSee also: ASE Certification

B

Battery CCA (Cold Cranking Amps)

A rating of how much power a battery can deliver to start an engine in cold weather. A replacement should meet or exceed the rating your owner's manual calls for, which matters more in cold climates. Read moreSee also: Battery Load Test, Jump-Start, Starter

Battery Load Test

A test that checks whether a battery can hold its voltage while delivering a heavy current, like starting the engine. A battery can show normal voltage at rest and still fail a load test. It helps separate a worn-out battery from a charging or drain problem. Read moreSee also: Battery CCA (Cold Cranking Amps), Alternator, Parasitic Drain, Multimeter

Battery Terminal Corrosion

White, green or bluish crust on the battery posts or cable clamps. It can block current and cause slow cranking or a no-start. Cleaning and tightening the connections sometimes fixes the problem; wear gloves and eye protection because the residue is acidic. Read moreSee also: Jump-Start, Battery Load Test

Bay

A single work space inside a repair shop, usually with a lift and equipment for one car. Mobile mechanics do not have bays, which is one reason they can have lower overhead and why some jobs still need a shop. Read moreSee also: Lift, Mobile Mechanic

Brake Fluid

The hydraulic fluid that carries the force of your foot on the pedal to the brakes at each wheel. It absorbs moisture over time, so carmakers list a flush interval in the owner's manual. A soft or sinking pedal or a low-fluid warning is a reason to stop and get the brakes checked. Read moreSee also: Brake Pads, Calipers, ABS (Anti-Lock Braking System)

Brake Pads

The friction pads that squeeze the rotors to slow the car, and the brake part replaced most often. Squealing, grinding or a longer stopping distance are common signs they are worn. Grinding usually means metal is hitting metal, so get them checked right away. Read moreSee also: Rotors, Calipers, Brake Fluid, Brake Rotor Resurfacing

Brake Rotor Resurfacing

Machining a thin layer off a rotor to make its surface smooth and flat again, also called turning. It only works if the rotor stays above the minimum thickness stamped on it. Many mechanics replace rotors instead, since new ones are widely available. Read moreSee also: Rotors, Brake Pads

C

Cabin Air Filter

The filter that cleans the air coming through your heating and AC vents. A clogged one can cause weak airflow or a musty smell. It is often quick to change, and the interval is in your owner's manual. Read moreSee also: Engine Air Filter, AC Recharge

Calipers

The clamp-like brake parts that hold the pads and press them against the rotors when you brake. A sticking caliper can make the car pull to one side, cause a burning smell or wear one pad much faster than the others. Read moreSee also: Brake Pads, Rotors, Brake Fluid

Catalytic Converter

An exhaust part that turns harmful gases into less harmful ones. It is often damaged by engine problems such as misfires, and it is a common target for theft. A rattle underneath, a rotten-egg smell or a failed emissions test can point to it. Read moreSee also: Misfire, Oxygen Sensor, Emissions Test

Check Engine Light

A dashboard warning (often an engine-shaped symbol) that the car's computer has found a fault, from a loose gas cap to a serious misfire. A steady light means get it checked soon; a flashing light usually means a severe misfire, so reduce speed and stop driving as soon as it is safe. Read moreSee also: OBD-II, Diagnostic Trouble Code (DTC), Misfire, Limp Mode

Coolant

Also called antifreeze, the fluid that carries heat away from the engine and keeps it from freezing in winter. Low coolant is a common cause of overheating. Use the type your owner's manual lists, and keep it away from pets and children because it is poisonous. Read moreSee also: Radiator, Thermostat, Water Pump, Head Gasket

Core Charge

A refundable deposit added to some parts, such as batteries, alternators and starters, to encourage returning the old part for rebuilding or recycling. You get it back when the old part is returned. Ask whether the mechanic handles the return and whether the quote already accounts for it. Read moreSee also: Alternator, Starter, Written Estimate

CV Axle

The drive shaft that sends power from the transmission to a front wheel (and on some cars the rear), with flexible constant-velocity joints at each end. A clicking noise when turning or grease sprayed inside the wheel from a torn rubber boot are common signs of wear. Read moreSee also: Wheel Bearing, Transmission Fluid

D

DEF (Diesel Exhaust Fluid)

A fluid, typically sold in jugs at gas stations and parts stores, that many modern diesel vehicles inject into the exhaust to cut emissions. It goes in its own tank, usually with a blue cap, never in the fuel tank. Letting it run out can cause the vehicle to limit its speed or refuse to restart. Read moreSee also: DPF (Diesel Particulate Filter), Limp Mode

Diagnostic Fee

What a mechanic charges to find the cause of a problem, such as testing, reading codes and checking wiring. It pays for time and skill even if no part is replaced. Many mobile mechanics credit it toward the repair if you go ahead with the work, so ask before booking. Read moreSee also: Trip Fee, Written Estimate, Scan Tool

Diagnostic Trouble Code (DTC)

A code, such as P0300, that the car's computer stores when it detects a fault. The code names the system or condition involved, not always the failed part. A mechanic uses it as a starting point for testing before replacing anything. Read moreSee also: OBD-II, Scan Tool, Freeze Frame Data, Check Engine Light

DPF (Diesel Particulate Filter)

A filter in a diesel exhaust system that traps soot. It cleans itself by burning the soot off during longer drives, a process called regeneration. Lots of short trips can clog it, which may trigger warning lights and reduced power. Read moreSee also: DEF (Diesel Exhaust Fluid), Limp Mode, Emissions Test

Drive Belt

A general term for a belt driven by the engine that runs accessories such as the alternator and AC compressor. Most modern cars use one serpentine belt; some older engines use several separate V-belts. Read moreSee also: Serpentine Belt, Alternator

E

Emissions Test

A state or local check that your car meets pollution rules, often by reading the OBD-II system or measuring exhaust. Requirements depend on where you live. A check engine light often means an automatic fail, and testing usually has to be done at a licensed station. Read moreSee also: OBD-II, Check Engine Light, Safety Inspection

Engine Air Filter

The filter that cleans air before it enters the engine. A very dirty one can reduce performance. It is inexpensive and easy to inspect, and is often checked during an oil change. Read moreSee also: Cabin Air Filter, Tune-Up

EV (Electric Vehicle)

A vehicle powered only by a battery and electric motors, with no gasoline engine. EVs still need tires, brakes, suspension, cabin filters and 12-volt battery service. Work on the high-voltage system requires special training and is usually done by a dealer or specialist. Read moreSee also: Hybrid Battery, Tire Rotation

Extended Warranty

Coverage sold to pay for certain repairs after the factory warranty ends. Many are technically service contracts from third parties, with their own rules about which repairs are covered and where. Read what is covered and how claims are paid before buying or relying on one. Read moreSee also: Warranty, Magnuson-Moss Warranty Act

F

Flat Rate

A single fixed price for a job, usually based on a labor guide's standard time, no matter how long the job actually takes. It lets you know the cost up front. Ask what happens if the mechanic finds another problem partway through. Read moreSee also: Labor Rate, Labor Guide, Written Estimate

Fleet Maintenance

Scheduled servicing and repair for a business's group of vehicles, such as vans or trucks. Mobile mechanics can often do it at the company's lot to cut downtime, and keep service records for each vehicle. Read moreSee also: Mobile Mechanic, VIN (Vehicle Identification Number)

Freeze Frame Data

A snapshot the car's computer saves when it sets a trouble code, recording things like speed, engine temperature and load at that moment. It helps a mechanic understand the conditions when the fault happened. Read moreSee also: Diagnostic Trouble Code (DTC), OBD-II, Scan Tool

Fuel Pump

The electric pump, usually inside the gas tank, that sends fuel to the engine. A failing pump can cause sputtering, stalling or a car that cranks but will not start. If you smell raw gasoline or see a fuel leak, do not start the car and keep sparks and flames away. Read moreSee also: Relay, Fuse, Limp Mode

Fuse

A small, cheap part that protects an electrical circuit by breaking when too much current flows. A blown fuse can knock out things like the radio, lights or fuel pump. If a new fuse blows again right away, there is a deeper fault to find. Read moreSee also: Relay, Parasitic Drain, Multimeter

H

Head Gasket

The seal between the engine block and the cylinder head. A failed head gasket can cause overheating, white exhaust smoke, coolant loss with no visible leak, or oil mixing with coolant. It is major internal engine work, usually done in a shop. Read moreSee also: Coolant, Radiator, Thermostat

Hybrid Battery

The high-voltage battery pack in a hybrid that powers the electric motor and stores energy from braking. It is separate from the ordinary 12-volt battery. Only trained technicians with proper equipment should work on it because of the risk of serious electric shock. Read moreSee also: EV (Electric Vehicle), Battery Load Test

I

Ignition Coil

The part that turns battery voltage into the high voltage a spark plug needs. Many modern engines have one coil per cylinder. A failing coil is a common cause of misfires and a flashing or steady check engine light. Read moreSee also: Spark Plugs, Misfire, Check Engine Light

Ignition Switch

The switch, worked by your key or start button, that powers the car's systems and signals the starter to crank. A faulty switch can cause a no-start, a stall, or accessories that cut out. Ignition switches have been the subject of safety recalls on some models. Read moreSee also: Starter, Relay, Recall

J

Jack Stands

Sturdy supports placed under a raised car so it cannot fall. A jack is only for lifting; never get under a car held up by a jack alone. A mobile mechanic working on the ground should use stands or ramps on firm, level ground. Read moreSee also: Lift, Lug Nuts

Jump-Start

Starting a car with a dead battery by borrowing power from another car or a portable jump pack using cables. It gets you going but does not fix the cause. If the car will not stay running or dies again soon, the battery, alternator or a parasitic drain may need testing. Read moreSee also: Battery CCA (Cold Cranking Amps), Parasitic Drain, Alternator, Roadside Assistance

L

Labor Guide

A reference book or database listing the standard time for common repairs on each vehicle. Mechanics use it to set flat-rate prices. Your bill is often based on that standard time, not the minutes the job actually took. Read moreSee also: Flat Rate, Labor Rate, Written Estimate

Labor Rate

The hourly price a mechanic charges for their time, separate from parts. Many mobile mechanics quote most jobs as one flat price instead, but the labor rate still shapes that price. Read moreSee also: Flat Rate, Labor Guide, Written Estimate

Lift

The hydraulic hoist a shop uses to raise a car overhead. Jobs such as exhaust, transmission and some suspension work are much safer and easier on a lift, which is why mobile mechanics usually send them to a shop. Read moreSee also: Bay, Jack Stands, Mobile Mechanic

Limp Mode

A protective mode where the car limits power, speed or gear changes after it detects a serious problem. It is meant to let you get off the road slowly and safely, not to keep driving normally. Get the car checked before driving it further. Read moreSee also: Check Engine Light, Diagnostic Trouble Code (DTC), Transmission Fluid

Lug Nuts

The nuts that hold each wheel on the car. They must be tightened to the carmaker's torque spec, usually in a star pattern. It is common advice to re-check them after a wheel has been removed and the car driven a short distance. Read moreSee also: Wheel Lock, Tire Rotation, Jack Stands

M

Magnuson-Moss Warranty Act

A US federal law about consumer product warranties. In general, a manufacturer cannot void your car's warranty just because you used an independent mechanic or aftermarket parts, unless it can show that work or part caused the problem. Keep receipts for all maintenance. Read moreSee also: Warranty, Aftermarket Parts, Extended Warranty

Misfire

When one or more cylinders fail to burn fuel properly, causing shaking, rough running or loss of power. Common causes include worn spark plugs, a bad ignition coil or fuel delivery problems. A flashing check engine light usually means a severe misfire that can damage the catalytic converter. Read moreSee also: Spark Plugs, Ignition Coil, Catalytic Converter

Mobile Mechanic

A mechanic who comes to you, at home, work or the roadside, with tools and parts in a van or truck. They handle most everyday repairs and maintenance on the spot. Jobs that need a lift or special equipment still go to a shop. Read moreSee also: Trip Fee, Lift, Roadside Assistance

Multimeter

A handheld tool that measures voltage, current and resistance. Mechanics use it to test batteries, fuses, wiring and parasitic drains, which helps confirm a fault before parts are replaced. Read moreSee also: Parasitic Drain, Battery Load Test, Fuse

O

OBD-II

The standard on-board diagnostic system in most cars sold in the US since the 1996 model year, with a plug usually under the dashboard near the steering column. A mechanic connects a scan tool to it to read trouble codes and live data. A code points to where a problem is, not always what part to replace. Read moreSee also: Diagnostic Trouble Code (DTC), Scan Tool, Check Engine Light, Freeze Frame Data

OEM Parts

Original equipment manufacturer parts, made by or for the carmaker to match what came on the car. They usually fit exactly and cost more. Some warranty or lease situations call for them, so check if that applies to you. Read moreSee also: Aftermarket Parts, Warranty

Oxygen Sensor

A sensor in the exhaust that measures oxygen so the engine computer can adjust the fuel mixture. A faulty one can turn on the check engine light, hurt fuel economy and cause an emissions-test failure. Read moreSee also: Catalytic Converter, Check Engine Light, Emissions Test

P

Parasitic Drain

Something that keeps drawing power from the battery after the car is turned off, such as a stuck relay, a glovebox light or an aftermarket accessory. It can leave you with a dead battery after the car sits. Mechanics track it down with a multimeter. Read moreSee also: Multimeter, Relay, Fuse, Jump-Start

Power Steering Fluid

The hydraulic fluid in cars with hydraulic power steering. A whining noise when turning or heavier steering can mean it is low or leaking. Many newer cars use electric power steering and have no fluid at all.See also: Serpentine Belt

Pre-Purchase Inspection

An independent check of a used car before you buy it, covering things like the engine, brakes, suspension, fluids, leaks and stored trouble codes. It helps you spot costly problems and negotiate. A mobile mechanic can often do it where the seller keeps the car. Read moreSee also: VIN (Vehicle Identification Number), Recall, OBD-II

R

Radiator

The finned part at the front of the car that releases engine heat into the air as coolant passes through it. Leaks, clogs or a failed cooling fan can lead to overheating. Never open a radiator or coolant cap on a hot engine, because the coolant is under pressure. Read moreSee also: Coolant, Thermostat, Water Pump

Recall

An official action by a carmaker, usually overseen by NHTSA, to fix a safety defect in certain vehicles, typically at no charge at a dealer. You can check for open recalls with your VIN on NHTSA's website. Recall repairs are done by dealers, not independent mechanics. Read moreSee also: VIN (Vehicle Identification Number), TSB (Technical Service Bulletin), Warranty

Refrigerant

The chemical in your AC system that absorbs heat from the cabin. Common types are R-134a in older cars and R-1234yf in many newer ones, and they are not interchangeable. Handling it is regulated by the EPA, so technicians need training and proper recovery equipment. Read moreSee also: AC Recharge

Relay

An electrically controlled switch that lets a small signal turn on a high-current circuit, such as the fuel pump, starter or cooling fan. A failed relay can cause a no-start or a part that will not switch on, and a stuck one can drain the battery. Read moreSee also: Fuse, Fuel Pump, Parasitic Drain

Roadside Assistance

A service, often from an auto club, insurer or carmaker, that helps with jump-starts, lockouts, flat tires, fuel delivery and towing. It gets you moving or to a shop, but usually does not include repairs. If you are stopped somewhere dangerous, get to safety first and call 911 if anyone is at risk. Read moreSee also: Tow, Jump-Start, Mobile Mechanic

Rotors

The metal discs attached to the wheels that the brake pads clamp onto. Worn or warped rotors can cause a vibration or pulsing in the brake pedal. They are often replaced together with pads when they are too thin or damaged. Read moreSee also: Brake Pads, Calipers, Brake Rotor Resurfacing

S

Safety Inspection

A periodic state-required check of items such as brakes, lights, tires and steering. Only some states require one, and it usually must be done at a licensed inspection station. A mobile mechanic can often fix what failed so you can pass the retest. Read moreSee also: Emissions Test, Brake Pads

Scan Tool

A device that plugs into the OBD-II port to read trouble codes and live data. Basic code readers are inexpensive; professional scan tools can also run tests and view data from systems such as ABS and airbags. Read moreSee also: OBD-II, Diagnostic Trouble Code (DTC), Freeze Frame Data

Serpentine Belt

One long rubber belt that drives parts such as the alternator, power steering pump and AC compressor. A squeal at startup or cracks on the belt are common warning signs. If it breaks, several systems can stop working at once, sometimes including engine cooling. Read moreSee also: Drive Belt, Alternator, Water Pump

Shocks and Struts

Suspension parts that control bouncing and keep the tires pressed to the road. Worn ones can cause excessive bouncing, nose-diving when braking and uneven tire wear. Struts also help support the car, so replacing them is often followed by a wheel alignment. Read moreSee also: Wheel Alignment, Tire Rotation

Shop Supplies Fee

A small charge on some repair bills for items such as rags, cleaners, lubricants and disposal. It should appear on your written estimate. Ask what it covers if it is not listed. Read moreSee also: Written Estimate, Trip Fee

Spark Plugs

Small parts that make the spark to ignite the fuel in each cylinder of a gasoline engine. Worn plugs can cause rough idling, misfires, slow acceleration and worse fuel economy. The replacement interval is in your owner's manual. Read moreSee also: Ignition Coil, Misfire, Tune-Up

Starter

The small electric motor that turns the engine over when you turn the key or press the start button. A single click, repeated clicking or no sound with working lights can point to the starter, though a weak battery or bad connection causes similar symptoms. Read moreSee also: Alternator, Ignition Switch, Jump-Start

Synthetic Oil

Engine oil made from chemically refined base oils, designed to resist breakdown and flow well in the cold. Many newer engines require it. Use the oil type and grade in your owner's manual. Read moreSee also: Engine Air Filter, Warranty

T

Thermostat

A valve that controls when coolant flows to the radiator so the engine warms up and then stays at the right temperature. One stuck closed can cause overheating; one stuck open can leave the engine running cold with weak cabin heat. Read moreSee also: Coolant, Radiator, Water Pump

Timing Belt

A toothed belt inside the engine that keeps the crankshaft and camshafts turning in step. It is replaced on a schedule in the owner's manual, because on many engines a snapped timing belt causes major internal damage. Some engines use a metal timing chain instead. Read moreSee also: Water Pump, Serpentine Belt

Tire Rotation

Moving tires to different positions on the car so they wear more evenly and last longer. The interval is in your owner's manual and is often done alongside an oil change. Read moreSee also: Wheel Balancing, Wheel Alignment, Lug Nuts, TPMS (Tire Pressure Monitoring System)

Tow

Moving a car that cannot be driven on a tow truck. Towing costs can add up quickly, which is one reason people call a mobile mechanic when the repair can be done where the car sits. Some cars, such as many all-wheel-drive models, should only be towed on a flatbed. Read moreSee also: Roadside Assistance, Mobile Mechanic

TPMS (Tire Pressure Monitoring System)

The system that warns you, usually with a horseshoe-shaped light with an exclamation point, when a tire is well below its recommended pressure. Check and fill your tires to the pressure on the driver's door-jamb sticker. If the light stays on or flashes, a sensor may need attention. Read moreSee also: Tire Rotation, Wheel Balancing

Transmission Fluid

The fluid that lubricates and cools the transmission and, in automatics, helps it shift. Dark, burnt-smelling or low fluid, slipping or harsh shifts are warning signs. Some transmissions have no dipstick and need special procedures to check or change fluid. Read moreSee also: Limp Mode, CV Axle

Trip Fee

A charge some mobile mechanics add for driving to you, also called a service-call fee. It is often waived or credited if the repair is done on the same visit. Ask whether it is included in the quote. Read moreSee also: Diagnostic Fee, Labor Rate, Mobile Mechanic

TSB (Technical Service Bulletin)

A notice from a carmaker to technicians about a known problem on certain models and the recommended fix. Unlike a recall, it is not always a safety issue or a free repair. It can save diagnosis time if your symptom matches one. Read moreSee also: Recall, VIN (Vehicle Identification Number), Diagnostic Trouble Code (DTC)

Tune-Up

An older term for routine engine maintenance. Today it usually means replacing spark plugs and checking filters, fluids and ignition parts. Since the meaning varies, ask exactly what a quoted tune-up includes. Read moreSee also: Spark Plugs, Ignition Coil, Engine Air Filter

V

VIN (Vehicle Identification Number)

The unique 17-character code for your vehicle, usually visible through the windshield on the driver's side and on your registration. Mechanics use it to order the right parts, and you can use it to check for recalls. Read moreSee also: Recall, TSB (Technical Service Bulletin), Pre-Purchase Inspection

W

Warranty

A carmaker's or seller's promise to fix certain defects for a set time or mileage. Parts and repair work can also carry their own warranties, so ask a mechanic what theirs covers and get it in writing. Keeping maintenance records helps with any claim. Read moreSee also: Extended Warranty, Magnuson-Moss Warranty Act, Recall

Water Pump

The pump that moves coolant through the engine and radiator. A leak near the front of the engine, a whining noise or overheating can point to it. On some engines it is driven by the timing belt, so the two are often replaced together. Read moreSee also: Coolant, Radiator, Thermostat, Timing Belt

Wheel Alignment

Adjusting the angles of the wheels so they point straight and sit correctly on the road. Signs you may need one include the car pulling to one side, an off-center steering wheel or uneven tire wear. It needs an alignment machine, so it is usually done at a shop. Read moreSee also: Tire Rotation, Wheel Balancing, Shocks and Struts, ADAS Calibration

Wheel Balancing

Adding small weights to a wheel and tire so it spins without wobbling. An unbalanced wheel often causes vibration in the steering wheel or seat at highway speeds. It needs a balancing machine, usually at a shop or a dedicated mobile tire service. Read moreSee also: Tire Rotation, Wheel Alignment

Wheel Bearing

The bearing that lets each wheel spin smoothly on its hub. A worn one often makes a humming or grinding noise that gets louder with speed or when turning. A badly worn bearing can affect steering and safety, so do not put it off. Read moreSee also: CV Axle, ABS (Anti-Lock Braking System)

Wheel Lock

A special lug nut that needs a matching key socket to remove, used to deter wheel theft. Keep the key somewhere you can find it, often the glovebox or trunk, and have it ready when a mechanic needs to take a wheel off. Read moreSee also: Lug Nuts, Tire Rotation

Wiper Blades

The rubber blades that clear your windshield. Streaking, chattering or skipping are signs they are worn. They are an inexpensive part that matters a lot for seeing in rain and snow. Read more

Written Estimate

A written list of the parts, labor, fees and total a mechanic expects to charge before starting work. Getting it in writing (a text or email counts) gives you something to compare against the final bill. Ask the mechanic to contact you before doing anything not on it. Read moreSee also: Flat Rate, Diagnostic Fee, Shop Supplies Fee