MOT & Servicing Glossary (UK)

Refilling the air-conditioning system with the correct refrigerant and oil, restoring cooling performance. Not part of an MOT, but common at services.

Prevents wheel lock under heavy braking. ABS warning light must go out; faults can cause an MOT failure.

Urea-based fluid used in diesel SCR systems to cut NOx emissions. Low AdBlue can trigger warnings and limp mode; level itself isn’t an MOT item, but emissions performance is.

A note of wear or deterioration that isn’t a failure today but needs monitoring or fixing soon. Appears on the MOT record.

Removes dust from intake air to protect the engine. Replaced during services per schedule.

If the SRS/airbag lamp shows a fault, it can fail the MOT because it indicates a safety system issue.

Adjusting steering geometry (toe, sometimes camber/caster) to reduce tyre wear and improve handling. Not part of MOT, but uneven wear can lead to advisories/fails.

Generates electricity to charge the battery and power systems while running. A weak alternator can cause warning lights and starting issues.

A bar linking left/right suspension to reduce body roll. Worn links/bushes can cause knocks and MOT faults.

Engine coolant with corrosion inhibitors. Checked at service; leaks may lead to overheating and repairs.

Pivot joint in suspension/steering arms. Excess play is a common MOT failure.

Load or conductance test to check battery health and cold-cranking ability, often done at service.

Headlight aim and cut-off shape must meet MOT specs to avoid dazzling other drivers.

Removing air from brake lines after repairs or fluid change to restore a firm pedal.

Rust in prescribed areas (e.g. within 30cm of seat-belt mounts, suspension, or brakes) can cause failure.

Rotors clamped by pads to slow the car. Excess wear, cracks or pitting can cause MOT fails.

Replacing hygroscopic fluid (typically every 2 years) to maintain boiling point and braking performance.

Flexible rubber/steel hoses to calipers. Bulges, cracks or leaks can fail the MOT.

Friction material that presses on discs. Below minimum thickness → advisory or fail.

Rigid lines carrying fluid. Corrosion or leaks can be dangerous and fail the MOT.

Friction linings used in drum brakes and some parking brakes. Worn or contaminated shoes reduce efficiency.

MOT machine measures brake force and imbalance across axles to published thresholds.

Replacing failed lamps (headlamps, indicators, stop lamps etc.). Lights are a top cause of MOT fails.

Rubber or polyurethane mounts isolating vibration. Excessive play or splits can fail the MOT.

Belt synchronising crank and cam(s). Replaced at time/mileage intervals; failure can destroy the engine.

Sensor for cam position used for timing and injection; faults trigger EML and poor running.

Converts harmful exhaust gases to meet emissions limits. Missing or damaged units can fail MOT.

System that locks/unlocks all doors. Not directly MOT-tested but must not compromise doors opening from inside.

Structural member of the body. Corrosion near key mountings is an MOT fail.

Typically pressure plate, friction disc and release bearing. Replaced if slipping, juddering or noisy.

Hydraulic cylinders operating the clutch. Leaks cause poor disengagement; fluid level checked at service.

Generates high voltage for spark plugs. Misfires raise emissions and can trigger an MOT fail on petrol cars.

Supports vehicle weight. Broken or displaced springs commonly fail MOTs.

Measures cylinder pressure to assess engine health (rings/valves/head gasket). Diagnostic, not MOT.

Suspension arm carrying bushes and ball joints. Wear leads to play and failures.

Rubber gaiter sealing grease in a CV joint. Split/greasy boots are common MOT fails.

Constant-velocity joint on driveshafts. Clicking on full lock suggests wear.

Indicator lamps (ABS, airbag, EML etc.). Certain illuminated faults can cause a fail.

Electronic fault-code reading and live data to pinpoint issues. Often the first step before repairs.

Two-piece flywheel that smooths vibration in many diesels. Failure causes rattle/jerk; usually replaced with the clutch.

Mirrors must be secure, provide a good view and have intact glass to pass the MOT.

Traps soot in modern diesels. Removal/tampering is illegal; excessive smoke/opacity causes MOT fails.

Short link joining anti-roll bar to suspension. Worn joints cause knocking and can fail MOT.

Recirculates some exhaust back to the intake to reduce NOx. Sticking valves cause smoke, rough running and EML.

MOT checks tailpipe gases (petrol) or smoke opacity (diesel) against limits for the vehicle’s age.

MIL that illuminates for emissions/engine faults. Persistent EML can cause an MOT fail.

Rear silencer that reduces noise. Holes or insecure hangers can fail the MOT.

Rubber/metal supports for the exhaust. Perished mounts lead to knocks and failures.

Escaping gases before the tailpipe. Excessive noise, fumes or weakened hangers can fail MOT.

Auxiliary belt driving alternator, pump(s) etc. Cracks/squeal suggest replacement at service.

Rear fog lamp required on most cars; operation and colour are MOT checks. Front fogs aren’t always required.

Removes contaminants from fuel. Service item; clogged filters cause hesitation or poor starting.

Supplies fuel under pressure to engine. Failure leads to non-start or cutting out.

Testing and replacing blown fuses for electrical circuits. Quick fix for inoperative lights or accessories.

Diesel pre-heaters aiding cold starts. Faults cause hard starting and smoke.

Must hold the vehicle effectively and evenly; cable/electric systems are tested on the MOT brake machine.

Checks for combustion gases in coolant (sniff test) or mixing of oil/coolant. Diagnostic, not MOT.

Manual/automatic adjustment of beam height. Inoperative systems can fail MOT.

Small radiator inside the cabin for heating. Leaks cause sweet smell, misting and wet carpets.

Horn must work and be of a continuous, uniform note to pass the MOT.

Wheel bearings allow rotation; play or roughness is an MOT fail.

Regulates engine idle speed on some petrol cars. Faults cause stalling or fluctuating revs.

Monitors oxygen in exhaust to adjust fueling. Faults raise emissions and fuel use; can cause MOT failures.

Security nut requiring a key. Keep the key in the car so wheels/tyres can be serviced.

Record of services, invoices or a digital service schedule. Helps maintain value and warranty compliance.

A more in-depth service (typically annual/12k miles) including more filters and checks than an interim service.

Measures manifold pressure or intake airflow to control fueling. Faults cause poor running and high emissions.

Hydraulic cylinder pressurising the brake system. Internal leaks cause a sinking pedal and reduced efficiency.

Smaller service between majors — typically oil & filter plus key safety checks.

Official test result recorded digitally; shows pass, with any advisories, or fail with defect categories.

DVSA service showing past passes, fails and advisories by number plate — useful before buying a car.

Follow-up MOT after fixing failures. Rules on free/partial retests depend on time elapsed and items repaired.

Plates must be secure, readable, and correct font/spacing. Incorrect or damaged plates can fail MOT.

Replacing engine oil with the correct grade and a new filter — the core of every service.

Seepage from gaskets/seals or components. Severe leaks can be dangerous and may fail MOT.

Filters air entering the cabin. Blocked filters reduce airflow and can mist windows.

Hydraulic fluid for PAS systems (not EV/EPAS). Level/condition checked at service; leaks can be dangerous.

Heat exchanger at the front of the car. Leaks/blocked fins cause overheating.

Short drive to confirm repairs or check noises, braking pull, steering and gearshift quality.

Seal around the top cover of the engine; common source of light oil leaks onto the block or manifold.

Selective Catalytic Reduction using AdBlue to reduce NOx in diesels. Faults increase emissions.

Belts and buckles must be secure, undamaged and latch/release properly. Pretensioner lights must behave correctly.

Resetting the service interval indicator after maintenance so the next due date/mileage is tracked.

MOT measures the density of smoke during acceleration to verify the DPF/engine are working correctly.

Igniters for petrol engines. Replaced on schedule; worn plugs cause misfires and poor economy.

Electric motor that cranks the engine. Clicking/no-crank can indicate starter, battery or cable issues.

Rack converts steering wheel movement to wheel angle; inner/outer joints wear and can fail MOT.

Mount and bearing at top of MacPherson struts. Wear causes clunks/creaks and vague steering.

Controls coolant flow to help the engine warm up quickly and stay at the right temperature.

Metal chain linking crank and cam(s). Can stretch or wear; noisy chains risk engine damage.

Outer steering joint. Play is a common cause of MOT failures and poor alignment.

Exhaust-driven compressor increasing engine power/efficiency. Whine, smoke or low boost suggest issues.

Correct pressures improve safety and wear. TPMS lights must work on newer cars (MOT item).

Legal minimum 1.6 mm across the central ¾ of the tread. Below this fails MOT.

Vehicle Identification Number must be present and legible. Checked during MOT.

Wash/wipe must clear the screen effectively; splits or poor spray can fail MOT.

Circulates coolant. Often replaced with cambelt kits; leaks or noise indicate failure.

Adding weights to prevent vibration through the steering/wheel at speed. Not an MOT check.

Allows smooth wheel rotation. Play/noise can fail MOT and damage hubs.

Sensor reading wheel rotation for ABS/ESC. Faults light the ABS lamp and can fail MOT.