- Camber
- The inward (negative) or outward (positive) tilt of a wheel viewed from the front. Wrong camber wears one tire edge and can pull toward the side with more positive camber.
- Caster
- The forward/rearward tilt of the steering axis viewed from the side. Positive caster gives straight-line stability and steering return; affects handling, not tire wear.
- Toe
- Whether the wheels point in (toe-in) or out (toe-out) viewed from above. Incorrect toe is the biggest cause of rapid, feathered tire wear; it is set last.
- MacPherson strut
- A front-suspension unit combining shock and coil spring that also serves as the upper steering pivot. A clunk on turns often means a worn strut bearing.
- Strut bearing (mount)
- The bearing at the top of a MacPherson strut that lets it rotate when steered. When worn it causes a clunk or bind during turns.
- Control arm
- A suspension link connecting the steering knuckle to the frame/body, locating the wheel while letting it move up and down. A bent arm (collision) throws off alignment.
- Ball joint
- A pivoting connection between the control arm and steering knuckle. Wear causes play, clunking, and uneven tire wear; a failed one can let the wheel collapse.
- Tie-rod end
- The steering link between the steering rack/center link and the knuckle. Wear causes steering play, wander, and toe wear.
- Steering knuckle (spindle)
- The cast part that holds the wheel hub/bearing and connects to the suspension and steering; it pivots to steer the wheel.
- Sway bar (stabilizer bar)
- A bar linking left and right suspension to resist body roll in turns, keeping the vehicle flatter and improving handling.
- Sway-bar link
- The connector between the sway bar and the suspension. A worn link rattles or clunks over bumps.
- Shock absorber
- A damper that controls spring oscillation. Worn shocks cause bouncing, poor ride control, and nose-dive under braking.
- Coil spring
- A spring that supports vehicle weight and absorbs road shock; a broken or sagging spring changes ride height and alignment.
- Leaf spring
- A layered steel spring used mainly on rear/truck suspensions to support load and locate the axle.
- Panhard rod (track bar)
- A lateral link that controls side-to-side movement of a solid axle, keeping it centered under the vehicle.
- Rack-and-pinion steering
- A steering gear where a pinion turns a toothed rack to move the tie rods, converting wheel rotation into side-to-side wheel movement.
- Power steering pump
- A belt-driven pump that supplies hydraulic pressure to assist steering. A whining noise often means low fluid or a failing pump.
- Electric power steering (EPS)
- Steering assist from an electric motor instead of a hydraulic pump, using a torque sensor to gauge driver effort.
- Torque sensor (EPS)
- A sensor that measures steering effort so the EPS motor applies the right amount of assist.
- Bump steer
- An unwanted change in toe as the suspension moves up and down, often from bent or worn steering/suspension parts after a collision.
- Wheel bearing
- The bearing that lets the wheel hub spin freely. A failing bearing growls or hums and the noise changes with speed or cornering load.
- Wheel hub
- The assembly the wheel bolts to, carrying the bearing and (often) the wheel-speed sensor.
- TPMS
- Tire Pressure Monitoring System — warns of low tire pressure via wheel sensors (direct) or wheel-speed data (indirect); often needs a relearn after service.
- Direct TPMS
- A TPMS that uses a pressure sensor inside each wheel; replacing a sensor or rotating wheels may require a relearn.
- Wheel alignment
- Adjusting camber, caster, and toe to spec so the vehicle tracks straight and tires wear evenly; required after structural collision repair.
- Thrust angle
- The direction the rear axle points relative to the vehicle centerline; a bad thrust angle makes the vehicle 'dog-track' or pull.
- Setback
- When one front wheel sits farther back than the other, often from collision damage, causing a pull and alignment trouble.
- Steering rack mounts
- The bushings securing the steering rack to the body; loose mounts cause clunks and vague steering.
- Idler arm / pitman arm
- Parts of a parallelogram steering linkage; the pitman arm is driven by the gearbox and the idler arm supports the other end.
- Center link (drag link)
- The steering link that connects the pitman and idler arms to the tie rods in a parallelogram steering system.
- Strut tower
- The body structure the top of a strut mounts to; a shifted tower from a collision changes camber and caster.
- Ride height
- The designed distance from the body to the ground; sagging springs lower it and alter alignment angles.
- Feathered tire wear
- A wear pattern with one side of each tread block higher than the other, caused by incorrect toe.
- Cupping (tire)
- Scalloped tire wear from worn shocks/struts or a bad wheel bearing letting the tire bounce.
- Double-wishbone suspension
- An independent suspension using upper and lower control arms (wishbones) to locate the wheel with good camber control.
- Lateral link
- A suspension arm that controls side-to-side wheel location in an independent rear suspension.
- Variable-ratio steering
- A steering rack whose ratio changes with wheel angle, giving easy parking and stable highway response.
- Steering angle sensor
- A sensor that reports steering-wheel position to stability control and ADAS; it often needs a relearn after alignment or repair.
- Voltage
- Electrical pressure (potential difference) that pushes current through a circuit, measured in volts.
- Current (amperage)
- The flow of electric charge through a circuit, measured in amperes (amps).
- Resistance
- Opposition to current flow, measured in ohms. High resistance from corrosion or loose grounds causes dim or intermittent operation.
- Ohm's law
- Voltage = current × resistance (V = I × R). It ties together the three basic electrical quantities.
- Series circuit
- A circuit with one path; the same current flows through every component and voltage divides across them.
- Parallel circuit
- A circuit with multiple paths; voltage is the same across each branch and current divides between them.
- Open circuit
- A break in the path so no current flows; the device is completely dead.
- Short to ground
- An unintended path letting current flow straight to ground, bypassing the load; it usually blows the circuit's fuse.
- Short to power (short circuit)
- An unintended connection between circuits or to a power feed that can overload and damage components.
- Voltage drop
- The voltage lost across a wire, connection, or load. Excess drop signals high resistance such as corrosion or a loose ground.
- Voltage-drop test
- Measuring volts lost across a segment while current flows, by placing meter leads across it under load — finds high resistance a key-on check misses.
- Digital multimeter (DMM)
- A meter that reads voltage, resistance, and current; the core tool for electrical diagnosis.
- Resistance measurement rule
- To read resistance correctly the circuit must be de-powered, or the meter reading is wrong.
- Fuse
- A sacrificial device that melts to break a circuit when current exceeds its rating, protecting the wiring.
- Fusible link
- A short length of smaller-gauge wire that melts to protect a high-current circuit, acting like a heavy-duty fuse near the battery.
- Circuit breaker
- A resettable overcurrent device that opens on overload and can be reset (manually or automatically).
- Relay
- An electrically operated switch that uses a small control current to switch a large load current.
- Relay vs. fuse
- A relay switches a circuit on/off; a fuse only protects it from overcurrent — they do different jobs.
- Diode
- A one-way valve for current; it allows flow in one direction and blocks the reverse, used for rectification and spike suppression.
- Alternator diodes
- Diodes in the alternator that rectify AC to DC; heat and vibration cause failure, often signaled by AC ripple in the output.
- Battery
- Stores chemical energy and supplies DC to start the engine and run electronics when the engine is off.
- State of charge
- How full a battery is; measured by voltage or with a tester. A fully charged 12-V battery reads about 12.6 V at rest.
- Alternator
- The belt-driven generator that charges the battery and powers the electrical system while the engine runs.
- Charging-system test
- Checks that the alternator maintains roughly 13.5–14.5 V at the battery under load with no excessive AC ripple.
- Starter motor
- The high-current motor that cranks the engine; a slow crank can be a weak battery or high resistance in the starter circuit.
- Ground (return path)
- The metal return path that completes a circuit back to the battery; a corroded ground causes many odd electrical faults.
- Parasitic draw
- Current drawn with the key off; an excessive draw drains the battery overnight.
- CAN bus
- Controller Area Network — a serial data network letting modules share information over a twisted pair, ended by terminating resistors.
- CAN terminator
- A resistor (typically 120 ohms) at each end of a CAN bus that prevents signal reflections and keeps data readable.
- Control module (ECU)
- A computer that monitors sensors and controls outputs; vehicles have many networked modules.
- Hall-effect sensor
- A sensor that produces a digital on/off signal as a magnetic field passes, used for speed and position sensing.
- Inductive (magnetic) pickup
- A sensor that generates an AC voltage as a toothed wheel passes, used for crank, cam, and wheel-speed sensing.
- Pulse-width modulation (PWM)
- Switching a circuit on and off rapidly and varying the on-time to control output like motor speed or lamp brightness.
- DTC
- Diagnostic Trouble Code — a code a module stores when it detects a fault, read with a scan tool to guide diagnosis.
- Pre-repair scan
- A diagnostic (health) scan before collision work to document existing trouble codes and create a baseline.
- Post-repair scan
- A scan after collision work to confirm codes are cleared, no new faults appeared, and which systems need calibration.
- ADAS
- Advanced Driver-Assistance Systems — cameras, radar, and sensors (lane keeping, auto braking) that must be calibrated after collision repair disturbs them.
- ADAS calibration
- Aiming and relearning ADAS cameras/radar to OEM spec after repair so the systems read the road correctly.
- Battery disconnect (collision)
- Disconnect the negative terminal first to de-power airbags and protect modules before welding/pulling; reconnect it last.
- Wiring repair (collision)
- Repair damaged harnesses with proper splices/connectors and protect them from heat, sparks, and pulling forces during repair.
- Headlight aiming
- Adjusting headlight beams to spec after front-end repair so they light the road without blinding oncoming drivers.
- Battery management system (BMS)
- On hybrids/EVs, the system that monitors and balances high-voltage battery cells and manages charging and temperature.
- Master cylinder
- Converts brake-pedal force into hydraulic pressure sent to the wheel brakes.
- Tandem master cylinder
- A master cylinder with two pistons feeding two independent circuits so braking remains if one circuit leaks.
- Brake fluid
- A hydraulic fluid that transmits pedal force; it is hygroscopic (absorbs water), which lowers its boiling point over time.
- Spongy brake pedal
- A soft, low pedal caused by air in the hydraulic lines or a fluid leak; it needs bleeding or leak repair.
- Brake bleeding
- Removing air from the hydraulic system to restore a firm pedal after any brake-line or component repair.
- Proportioning valve
- Limits hydraulic pressure to the rear brakes during hard stops to keep the rear wheels from locking before the fronts.
- Disc brake
- A brake using a caliper to squeeze pads against a rotor; good at shedding heat and resisting fade.
- Brake caliper
- The clamp that presses the pads against the rotor; a sticking caliper drags and causes a pull and uneven wear.
- Brake rotor (disc)
- The spinning disc the pads clamp; a warped rotor causes a pulsing pedal and steering-wheel shudder.
- Warped rotor
- An out-of-flat or thickness-varying rotor that causes a pulsing brake pedal and vibration when braking.
- Brake pads
- Friction material pressed against the rotor; uneven pad wear points to a sticking caliper or slide pins.
- Drum brake
- A brake using shoes that press outward against a spinning drum, common on rear axles of lighter vehicles.
- Brake booster
- A vacuum (or hydraulic) assist that multiplies pedal force so braking takes less effort.
- Brake pull
- A vehicle that veers when braking, usually from a dragging caliper or contaminated pad on one side.
- ABS
- Anti-lock Braking System — keeps wheels from locking during hard braking using wheel-speed sensors and a hydraulic modulator.
- Wheel speed sensor
- Reads each wheel's rotational speed for ABS and stability control; a damaged sensor or tone ring sets a fault.
- Tone ring (reluctor)
- The toothed ring a wheel-speed sensor reads; a bent or damaged ring after a collision causes erratic readings.
- ABS modulator
- The hydraulic unit that rapidly releases and reapplies brake pressure to a wheel to prevent lockup.
- Electronic stability control (ESC)
- Builds on ABS, using steering-angle and yaw inputs to brake individual wheels and keep the vehicle on its path.
- Electronic parking brake (EPB)
- A parking brake applied by an electric motor/actuator instead of a cable and lever.
- Split-diagonal brake system
- A dual circuit pairing one front and the opposite rear wheel per circuit so one failure still leaves braking on both ends.
- Brake fluid pressure sensor
- Reports hydraulic pressure to the ABS/stability module; a faulty sensor can disable ABS and set a code.
- Refrigerant
- The fluid (R-134a or R-1234yf) that absorbs and releases heat as it cycles through the A/C system; it must be recovered, not vented.
- R-1234yf
- A low-global-warming refrigerant used in newer vehicles, replacing R-134a; it requires its own service equipment.
- A/C compressor
- Pumps and compresses low-pressure refrigerant vapor into a hot, high-pressure gas, driving the refrigerant loop.
- Condenser
- The front-mounted heat exchanger where the hot high-pressure gas sheds heat and condenses into a liquid; often damaged in front collisions.
- Evaporator
- The dash heat exchanger where cold low-pressure refrigerant absorbs heat from cabin air, cooling the air the blower delivers.
- Orifice tube
- A fixed-size metering restriction (used with an accumulator) that drops refrigerant pressure before the evaporator.
- Thermostatic expansion valve (TXV)
- A variable metering valve (used with a receiver-drier) that adjusts refrigerant flow based on evaporator temperature.
- Receiver-drier
- Stores refrigerant and removes moisture with a desiccant in TXV systems, on the high side.
- Accumulator
- Stores refrigerant and removes moisture in orifice-tube systems, on the low side, protecting the compressor from liquid.
- Desiccant
- A moisture-absorbing material inside the receiver-drier or accumulator that keeps water out of the refrigerant.
- High side / low side
- The A/C loop split by the metering device into a hot high-pressure side (compressor to metering) and a cold low-pressure side (metering to compressor).
- Refrigerant recovery
- Capturing refrigerant with approved equipment before opening the system; venting it is illegal and harmful.
- Evacuation
- Pulling a vacuum on the A/C system to remove air and boil off moisture before recharging.
- Recharge
- Refilling the A/C with the correct refrigerant type and exact specified amount after service.
- EPA Section 609
- The federal rule requiring certified technicians and approved equipment to service motor-vehicle A/C systems.
- Blend door
- An air door in the HVAC case that mixes heated and cooled air to set cabin temperature; a stuck actuator gives wrong temperatures.
- Mode door
- An HVAC door that directs airflow to the vents, floor, or defrost; a failed mode-door actuator misroutes airflow.
- HVAC actuator
- A small electric motor that moves a blend or mode door; a faulty actuator clicks or sets the wrong temperature/airflow.
- Heater core
- A small radiator in the dash that uses engine coolant to heat the cabin; a leak fogs the windshield with sweet-smelling vapor.
- Cabin air filter
- A filter that cleans incoming HVAC air; when clogged it reduces airflow from the vents.
- Thermistor (HVAC)
- A temperature-sensitive resistor used to sense cabin or evaporator temperature for climate control.
- Sunload sensor
- A sensor that detects sunlight intensity so automatic climate control compensates for solar heating.
- Evaporator frosting
- Ice on the evaporator from excess moisture or a stuck-low temperature, which blocks airflow and cuts cooling.
- Poor cooling at idle
- A/C that cools well at speed but poorly at idle usually points to weak airflow over the condenser (fan) or low idle performance.
- Thermostat
- A temperature-controlled valve that blocks coolant flow to the radiator until the engine warms, then opens to regulate temperature.
- Stuck-closed thermostat
- Blocks flow to the radiator, causing the engine to overheat.
- Stuck-open thermostat
- Lets coolant flow too soon, keeping the engine too cool and weakening cabin heat and economy.
- Water pump
- The belt- or chain-driven pump that circulates coolant through the engine and radiator.
- Radiator
- The heat exchanger where airflow sheds heat from the coolant; often damaged in a front collision.
- Radiator cap
- A pressure cap that seals the system and raises the coolant boiling point; its vacuum valve returns coolant from the recovery tank.
- Coolant (antifreeze)
- A water/glycol mix that transfers heat, resists freezing and boiling, and protects against corrosion.
- Coolant concentration
- Usually a 50/50 coolant-to-water mix; the wrong ratio reduces freeze/boil protection and corrosion resistance.
- Coolant recovery tank
- Holds expanding coolant and returns it as the engine cools, keeping the system full and air-free.
- Cooling fan
- An electric or clutch-driven fan that pulls air through the radiator at low speed and idle.
- Fan clutch
- A thermostatic coupling that engages the engine-driven fan when the radiator is hot.
- Airlock
- Trapped air after a refill that blocks coolant flow and causes localized overheating even with no leaks; bleed the system.
- Cooling-system pressure test
- Applying pressure to the system to find external leaks or a cap that won't hold pressure.
- Combustion-gas (block) test
- A test that detects exhaust gases in the coolant, confirming a head-gasket or cracked-head leak.
- Heater core (cooling link)
- Part of the cooling circuit; a heater control valve or core directs hot coolant for cabin heat.
- Coolant temperature gauge
- Displays engine coolant temperature; a steady climb past normal warns of overheating.
- Overheating causes
- Low coolant, a stuck thermostat, a failed water pump or fan, a clogged radiator, an airlock, or a head-gasket leak.
- Rust-colored coolant
- Indicates internal corrosion or old/contaminated coolant; the system should be flushed and refilled with fresh coolant.
- Cooling-system flush
- Draining and cleaning the system to remove rust, scale, and old coolant, then refilling with the correct mix.
- Weep hole (water pump)
- A small drain hole on the pump; coolant leaking from it signals a failing pump seal.
- Torque converter
- A fluid coupling connecting the engine to an automatic transmission; it idles, multiplies torque at low speed, and locks up at cruise.
- Torque-converter lockup
- A clutch that mechanically links the converter at cruising speed to eliminate slip and improve fuel economy.
- Flexplate
- The plate that bolts the torque converter to the crankshaft; a crack causes a noise that changes with load.
- Automatic transmission
- A gearbox that shifts gears automatically using hydraulics, clutches, and (in many) planetary gearsets.
- Manual transmission
- A driver-shifted gearbox using a clutch to connect and disconnect engine power.
- Clutch
- The driver-controlled coupling in a manual transmission that connects and disconnects engine power for shifting.
- Synchronizer (synchro)
- A device in a manual transmission that matches gear speeds for smooth, quiet shifting; worn synchros cause grinding.
- Gear whine
- A whining noise from worn gears, low fluid, or improper gear mesh in a transmission or differential.
- Dual-clutch transmission (DCT)
- An automated manual using two clutches for fast, smooth shifts without a torque converter.
- Differential
- A gearset that splits drive torque to the wheels while letting them turn at different speeds in a corner.
- Limited-slip differential
- A differential that sends torque to the wheel with grip when one wheel slips, improving traction.
- CV joint
- A constant-velocity joint that lets a drive axle deliver power smoothly while the wheel steers and travels.
- CV boot
- The rubber boot that holds grease in and dirt out of a CV joint; a tear leads to a clicking, failing joint.
- CV-joint click
- A rhythmic click that gets louder when turning at low speed — the classic sign of a worn outer CV joint.
- Half-shaft (drive axle)
- The shaft with CV joints that delivers power from the differential to a front (or independent rear) wheel.
- U-joint (universal joint)
- A joint on a driveshaft that allows angle changes; wear causes a clunk on acceleration and a speed-related vibration.
- Driveshaft
- The shaft carrying power from the transmission to the rear axle; an unbalanced shaft vibrates at higher speeds.
- Driveline vibration
- A vibration that rises with vehicle speed, often from a worn U-joint or an unbalanced/bent driveshaft.
- Transfer case
- A gearbox in 4WD/AWD that splits power between the front and rear axles.
- Viscous coupling
- An AWD device that transfers torque between axles using fluid shear; a failure causes binding or lost AWD.
- Transmission mount
- A mount that supports the transmission and dampens vibration; a broken mount lets the drivetrain shift and clunk.
- Axle (drive axle) inspection
- Checking axles, joints, boots, mounts, and the driveline for damage and leaks after a collision.
- Oxygen (O2) sensor
- Measures oxygen in the exhaust and tells the computer if the mixture is rich or lean for closed-loop fuel control near 14.7:1.
- Catalytic converter
- An exhaust device that converts carbon monoxide, hydrocarbons, and NOx into less harmful gases; a plugged one kills power.
- Carbon monoxide (CO)
- A colorless, odorless, poisonous exhaust gas; a crash-damaged exhaust can leak it into the cabin — a key safety check.
- Mass airflow (MAF) sensor
- Measures the air entering the engine so the computer can meter fuel; a faulty MAF causes poor running and drivability codes.
- Fuel pressure regulator
- Maintains the correct fuel-rail pressure for the injectors; a fault causes rich or lean running.
- Fuel injector
- An electronic valve that sprays metered fuel into the intake or cylinder; a clogged or leaking injector skews the mixture.
- Gasoline direct injection (GDI)
- Sprays fuel directly into the cylinder at high pressure, using a high-pressure fuel pump for efficiency and power.
- EGR valve
- Exhaust Gas Recirculation valve — routes inert exhaust into the intake to lower combustion temperature and cut NOx.
- Turbocharger
- An exhaust-driven compressor that forces more air into the engine for more power.
- Intercooler
- A heat exchanger that cools the compressed intake air from a turbocharger, increasing air density and power.
- Air filter
- Filters intake air; a clogged filter restricts airflow and can richen the mixture and cut power.
- Fuel-line inspection (collision)
- Checking fuel lines and the tank for leaks and damage after a crash — a fuel leak is an immediate fire hazard.
- Restricted exhaust
- A crushed or plugged exhaust that chokes the engine, causing power loss especially at higher RPM.
- Exhaust leak
- A crack or loose joint that lets exhaust escape; near the cabin it is a carbon-monoxide hazard and must be repaired.
- Supplemental restraint system (SRS)
- The airbags, seat-belt pretensioners, crash sensors, and control module that protect occupants in a crash, supplementing the seat belts.
- Airbag (air bag)
- An inflatable cushion that deploys in a crash to cushion the occupant; a deployed bag must be replaced, never reused.
- SRS control module
- The computer that reads crash sensors and deploys airbags and pretensioners; it stores crash and fault data.
- Crash (impact) sensor
- Detects the rapid deceleration of a collision and signals the SRS module to deploy the restraints.
- Rollover sensor
- Detects a vehicle tipping over so the SRS can deploy side curtains and tension the belts.
- Seat-belt pretensioner
- A one-time pyrotechnic/mechanical device that instantly retracts the belt in a crash to remove slack before the airbag inflates.
- Pretensioner replacement
- A fired pretensioner is a one-time device and must be replaced, not reset, after deployment.
- Clockspring (coil spring connector)
- A coiled ribbon that keeps the driver-airbag and steering-wheel circuits connected as the wheel turns.
- Side-impact airbag
- An airbag that deploys from the seat or door for side crashes, protecting the torso or pelvis.
- Curtain airbag
- A roof-rail airbag that drops to cover the side windows, protecting the head in side impacts and rollovers.
- Seat-belt retractor
- The spool that takes up belt slack and locks in a crash; a faulty retractor won't lock or retract properly.
- Occupant classification sensor
- A seat sensor that detects occupant weight/presence so the system can enable or suppress the passenger airbag.
- SRS de-power procedure
- Disconnect the battery and wait the manufacturer-specified time before working near airbags to prevent accidental deployment.
- Live (undeployed) airbag handling
- Carry the module with the cover facing away and set it face-up; it is an explosive device handled per the OEM procedure.
- Airbag disposal
- Deploying or disposing of live airbags only per OEM/manufacturer and regulatory procedures.
- SRS warning light
- A dash light that, when lit, means a stored restraint-system fault that must be scanned and repaired.
- Head restraint
- The headrest positioned so its top is near the top of the occupant's head to reduce whiplash in a rear impact.
- Post-repair SRS scan
- Scanning the restraint system after repair to confirm no faults remain before returning the vehicle.
