Common MOT failure and advisory wording explained by a UK mechanic, grouped by the area of the car it relates to.
Around 30% of UK cars fail the MOT first time. The four biggest causes are lighting and signalling, suspension, brakes and tyres — together they account for well over half of all failures. Most are cheap to spot beforehand. A retest within 10 working days at the same garage is usually free.
Answered by Bob — 32 years on the tools, DVSA-approved MOT centre, Birnam, Perthshire.
Around 30% of UK cars fail the MOT first time. The four biggest causes are lighting and signalling, suspension, brakes and tyres — together they account for well over half of all failures. Most are cheap to spot beforehand. A retest within 10 working days at the same garage is usually free.
Answered by Bob — 32 years on the tools, DVSA-approved MOT centre, Birnam, Perthshire.
Dangerous, major and minor — what the three verdicts mean
Since 2018 every MOT defect is graded. A dangerous defect means the car is an immediate risk and must not be driven away — driving it is an offence even with a valid certificate still in date. A major defect is a failure and must be repaired and retested. A minor defect is not a failure but is recorded on the certificate, and an advisory is a warning that something will need attention before long. Advisories are worth reading: most of next year's failures are on this year's advisory list.
The failure categories that catch most UK cars
Lighting and signalling is the single biggest cause of failure and the cheapest to avoid — a blown bulb, a misaimed headlamp, a cracked lens. Suspension comes next: worn top mounts, tired shock absorbers, split bushes and corroded springs. Brakes follow: pads below the limit, scored discs, imbalance across an axle, a seized caliper, or a corroded brake pipe. Tyres fail on tread under 1.6mm across the central three-quarters, sidewall damage, or the wrong speed rating. Then driver's view — chipped screens in the swept area and torn wipers. Emissions and the exhaust round it off, along with an illuminated engine management, airbag, ABS or power steering warning light, each of which is an automatic major failure.
Corrosion — where cars in Scotland lose their MOT
Salted winter roads are brutal on brake pipes, subframes, sills and suspension mounting points. A tester can only fail corrosion in a prescribed area, but that includes anything within 30cm of a seatbelt mounting, steering or suspension component. Perforated sills on a fifteen-year-old car can be the difference between an MOT pass and a write-off decision, so it is worth getting a look underneath before the test rather than after.
What a failure costs you
A partial retest is free at the same garage if the car stays there and the repair is done within the working day, or within ten working days if it leaves and comes back for a limited list of items. Beyond that a full retest fee applies. Typical repairs: bulbs £5–£25, wiper blades £15–£35, front pads and discs £180–£350, a pair of rear shocks £200–£400, a brake pipe £80–£180, a tyre £55–£150, a windscreen £90–£350 depending on sensors. The £54.85 test fee is the same everywhere — it is the statutory maximum for a Class 4 car.
Can you drive a car that has failed?
Only if the previous certificate is still valid and the failure is not a dangerous defect, and even then only to a booked repair. If the old certificate has expired, the only legal journeys are to a pre-booked MOT or to a garage for repairs. A dangerous defect means it should not move under its own power at all.
How to stop most of it happening
Twenty minutes the weekend before the test catches most of it: walk round with someone pressing the pedals and indicators to check every bulb, top the screenwash, check wipers for tears, check tread depth with a 20p piece, check tyre pressures, listen for knocks over speed bumps, and make sure no warning lights stay lit. Bob sees the same handful of avoidable failures every week, and almost all of them cost under £30 to put right beforehand.