Why cars fail their MOT

The big five

Year after year, DVSA's figures show the same categories at the top of the fail list:

1. Lights and signalling — the single biggest cause. A blown bulb, a cracked lens, a number-plate light out, headlamps aimed too high. Cheap parts, easy fail.
2. Suspension — worn shock absorbers, broken springs, play in ball joints and bushes. You often don't feel it developing because it happens slowly.
3. Brakes — pads below the limit, discs worn or scored, a sticking caliper, a handbrake that doesn't hold, corroded pipes.
4. Tyres — tread below 1.6mm, cuts, bulges, cords showing, or the wrong size fitted. Below 1.6mm is graded dangerous, so the car can't be driven away.
5. Driver's view — windscreen chips in the wiped area, split wiper blades, empty washer bottle, things dangling from the mirror, a sat-nav mount in the wrong place.

Behind those come emissions (diesel smoke and petrol readings), exhaust leaks, corrosion near structural points, seatbelts that don't retract, and — since 2018 — any warning light that's on for the engine, ABS, airbag or electronic parking brake.

Which of these you can check yourself

Lights, tyres, washers, wipers, the horn, and the warning lights on the dash. That's most of category one, all of five and a chunk of four. Ten minutes with a friend on the drive: here's the checklist.

Which you can't

Brakes and suspension need the car in the air with a trained eye on it. That's where a service or a free brake check before the MOT earns its keep — you find out on your terms rather than the tester's.

If it does fail

Every item is graded dangerous, major, minor or advisory, and each grade means something different for what you can do next. Can you drive it? is the first question; Ask Lois will explain the actual items on your certificate.