The Top Reasons Cars Fail Their MOT

The Top Reasons Cars Fail Their MOT

Most MOT failures come down to a small number of common faults. Lighting and signalling problems are the single biggest cause, followed by suspension, brakes, tyres and visibility. The encouraging part is that many of these are cheap and quick to put right before a test.

The pattern is remarkably consistent year after year. Lighting alone accounts for roughly three in every ten failures, often something as simple as a blown bulb. Because so many failures are small items, a short check before your test can turn a likely fail into a comfortable pass. Our guide on What an MOT Checks lists everything a tester inspects.

Knowing where cars trip up puts you a step ahead. The rest of this guide breaks down the top failure areas and the simple checks that head them off, so your car has the best chance of passing first time.

Where Cars Fail Most Often

The chart below shows the typical share of MOT failures by category, based on national testing data. It makes clear just how much lighting dominates the list.

The striking thing is how many of the top causes are inexpensive to sort. A bulb or a wiper blade costs very little, so a quick check beforehand pays for itself many times over. Our guide on When Your Car Fails an MOT explains what happens if a car does fail.

The Failure Areas to Watch

Four areas cause the great majority of failures. Knowing what the tester looks for in each helps you check them yourself before the test.

Tyres round out the big four. Tread must be at least 1.6mm across the central three quarters of the tyre, while cuts or bulges are an automatic fail. Our guide on Tyres and the MOT covers the tyre rules in full.

Simple Checks to Avoid a Fail

A few minutes of checking the day before can save a wasted test. None of these jobs are difficult, yet together they cover a large share of the faults that catch cars out.

These simple steps head off the majority of common failures. Our guide on When Your Car Fails an MOT explains what to do if the car does not pass despite your best efforts.

Why Lighting Tops the List Every Year

It can seem surprising that something as simple as lighting is the biggest single cause of failure, ahead of brakes and tyres. The reason is partly that a car has so many bulbs, from headlights and brake lights to indicators, fog lights and number plate lamps. Any one of them failing is enough to fail that part of the test, so the odds add up across the whole car.

Bulbs also fail without warning and often without the driver noticing, especially a brake light or a rear bulb you rarely see. That is why a two minute walk around with a helper is the single most valuable pre test check you can do. It costs nothing, catches the most common fault of all then leaves you free to focus on the bigger items. Our guide on What an MOT Checks lists every lighting item a tester inspects.

Pass First Time

This guide is part of our full MOT Guides hub, where the testing, cost and rules articles sit together so you can move to the exact detail you need next. When it is time to book, our team offers full MOT testing and repairs from our centre in Ely. You may also find it useful to read When Your Car Fails an MOT, Tyres and the MOT and Brakes and the MOT.

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