Why cars actually fail the MOT

The two that dominate

Across all recorded MOT defects, lighting accounts for roughly 24.7% and suspension for around 19.5%. Between them that is nearly half of everything logged.

The gap between those two is the interesting part. A blown bulb is a few pounds and five minutes. Suspension — springs, shock absorbers, bushes, drop links — is more often somewhere between a hundred and five hundred pounds in parts and labour.

Why lighting is worth checking yourself

It is the one category you can genuinely rule out in your own driveway. Headlights on main and dipped, sidelights, indicators front and back, brake lights, reversing light, fog lights, number plate lights. Reverse against a wall or a window at dusk and you can see almost all of them alone.

We would rather tell you a bulb is out before the test than record it as a failure and have you come back. Bring it in the week before if you want us to look.

Age changes everything

The failure rate is not flat. It sits near 14% at the first test, when a car is three years old, and climbs steadily to the mid-thirties by thirteen to fifteen years. Nothing about that is surprising, but it does mean a fifteen-year-old car with no recent work is a different proposition to a five-year-old one.

What actually reduces the risk

• Service the car to the schedule rather than to the warning light
• Get advisories looked at while they are advisories, not after they become failures
• Check every bulb the week before the test
• Tyres: tread, pressures and sidewalls, all four plus the spare if you carry one