Common MOT failure reasons — and how to avoid them

DVSA publishes the same story annually: lamps, tyres, brakes, suspension and visibility account for a huge share of fails. None of those require a diagnostic laptop. They require looking, listening, and not leaving the test to the last afternoon of the certificate.

Tyres

The legal minimum tread is 1.6mm across the central three-quarters of the tyre. Testers also fail tyres for cords showing, bulges, deep cuts, and incorrect size or load rating. “Close to the legal limit” is an advisory you should treat as a fail that has not happened yet.

Avoid it: check all four tyres and the spare if the vehicle has one that is part of the test. Measure the inner edge as well as the outer — worn wishbones and poor tracking eat the inside first. Inflate to the door-sticker pressures when the tyres are cold. A bald tyre is also a police matter, not just an MOT matter.

Brakes

The MOT measures brake performance and balance, not whether the pedal “feels fine”. Uneven discs, seized calipers, worn pads, leaking cylinders and a weak parking brake are routine fails. A car that pulls to one side under braking is already telling you the test will go badly.

Avoid it: on a quiet road, perform a controlled stop from 20–30 mph and a firm parking brake check on a gentle slope. Listen for grinding. Look through the wheels at pad thickness if you can see it. If the history already shows brake advisories, do not wait for the tester to upgrade them to a major defect.

Lights, indicators and electrical

Blown bulbs are the most avoidable fail in the country. Headlamp aim, cracked lenses, broken rear fog lamps, number-plate lamps and missing reflectors sit in the same family. Aftermarket HID or LED conversions that dazzle oncoming traffic fail aim and glare checks.

Avoid it: switch on every lamp, including hazards, fog lamps and the registration plate lights. Walk around the car. If a cluster is damp inside, budget a repair — condensation can take aim and output below standard.

Suspension and steering

Worn ball joints, split gaiters that have let grease out, leaking shock absorbers, cracked coil springs and excessive play in the steering rack are classic fails. They are also the defects that make a car feel “a bit loose” for months while the owner pretends it is normal.

Avoid it: bounce each corner. The car should settle, not keep bouncing. Listen for knocks over speed bumps. Look at spring coils for rust fractures, especially on the rear of older hatches. If the MOT history already lists play in a joint, assume it has not healed itself.

Visibility: wipers, washers, glass and mirrors

A windscreen chip or crack in the driver’s view (broadly the area swept by the wipers in front of the driver) is a fail if it is large enough. Worn blades that smear, empty washer bottles, and missing mirrors are embarrassingly common.

Avoid it: fill the washer bottle with proper fluid, replace blades that chatter, and get chips repaired before they spread. Sit in the driver’s seat and look through the glass the way a tester will.

Emissions and exhaust

Diesels with neglected DPFs, petrol cars with failing catalysts, and exhausts held on by gravity produce both emissions and noise fails. A car that has been used for five-minute journeys may fail a smoke or catalyst test even if it “drives fine”.

Avoid it: service it on time, fix the engine management light before the MOT, and give a diesel a proper run if it has been city-bound. Do not empty additives into a problem you have not diagnosed. Testers are not required to ignore a glowing MIL.

Body, structure and corrosion

Sharp edges, insecure bumpers, corroded brake and fuel lines, and rust in prescribed areas (sills, chassis, seat belt mounts, suspension towers) fail because they are safety items, not cosmetic ones. A tidy respray can hide this. A tester with a tap hammer will not.

Avoid it: look underneath on a dry day. Pay attention to the sills, jacking points and around the rear axle. If you are buying, never skip this because the MOT is “just done”. A pass last month can sit next to corrosion that is already close to the limit.

Registration plates and VIN

Illegal fonts, spaced-out plates, dirty inscriptions and missing VIN markings fail. They are also an insurance and police problem. If you bought “show plates”, put the legal ones back on before the test.

How to use failure history when you buy

Search the plate, then read every fail, not only the latest pass. Ask for receipts that match the defect text. A parking-brake fail with a receipt for cables is reassuring. A dangerous brake disc fail with no paperwork is a walk-away signal. Recurring tyre or corrosion fails suggest the car is being kept on a minimum budget. Price it accordingly, or leave it for someone else.