Why Do Cars Fail MOTs?

It’s an age old question, but unlike most of those troubling car maintenance questions we ask ourselves, the question of why cars fail MOTs actually has an answer. Well, several answers to be precise.

Here’s my attempt at listing the main reasons your car is likely to fail its MOT.

Why do cars fail MOTs?

So, the answer to this is pretty simple – because they don’t meet the legal standards set by the government in one or more specific areas, like safety, emissions, condition or performance.

The bad news is that your car can fail it’s MOT for quite a few reasons. The good news is that most failures can be easily prevented with a bit of prior car maintenance, and by checking your car over quickly before you send it for it’s MOT.

My blog, A Guide To MOT Testing, goes into the exact things that your car is tested on in more detail so that you can know what to check, but here’s a brief rundown.

Things your car is tested on in an MOT:

  • Vehicle Identification Number and number plate
  • Lights
  • Steering
  • Suspension
  • Wipers and washers
  • Windscreen
  • Horn
  • Seats and seatbelts
  • Fuel system
  • Emissions
  • Bodywork
  • Doors
  • Wheels and tyres
  • Brakes

The types of faults in an MOT test

Few cars emerge as completely perfect when it comes to the MOT test.

As of May 2018, faults in an MOT test are now split into 4 kinds called:

  1. Dangerous defects
  2. Major defects
  3. Minor defects
  4. Advisories

Dangerous Defects

Just one of these faults means that your car fails its MOT instantly. Dangerous faults include all of your brake lights not working, all of your seatbelts being broken and your doors not closing and locking properly.

This category was added in the recent 2018 changes to the MOT terminology to make it clearer to drivers that these faults are a danger to safety.

Major Defects

These are serious defects that will cause an instant MOT. For the types of major defects, think of things that might not have an immediate impact on safety but are still very serious, like emissions breaching the permitted amount.

Main reasons why cars fail MOT tests

The Government’s own website, Gov.UK, has some interesting stats on the most common reasons that cars fail their MOT tests. It says that:

  • Poor tyre condition and incorrect air pressure makes up 10% of all MOT faults.
  • Lighting and signalling problems make up 30% of all MOT faults.
  • Mirrors, washers and wipers contributed to 8.5% of MOT faults when it comes to the ‘Driver’s clear view of the road’ part of the test.
  • Brake problems make up around 9.6% of all MOT faults.

Tyre problems

Cuts, bulges and damages to your tyres are a major problem that can cause an MOT failure. As is not having the right levels of tread depth and air pressure. The minimum permitted tread depth is 1.6mm so make sure you check this regularly and get a new tyre when it comes close to this depth.

Brake problems

Brake problems are a very serious problem and can cause an instant MOT failure. You can check their condition when you first set off in your car by listening and feeling how the car reacts to braking.

If you hear an odd sound when you brake, or if braking pulls the car to one side, you should stop driving immediately and contact a garage.

Lighting and signalling problems

Checking your lights is really easy, so there’s no excuse to be failing your MOT test for faults associated with your lights. You just need to tap them lightly to see if they’re damaged or loose. If they are, just replace them.

Signalling problems could be more challenging to fix, so, if you spot a problem, it’s probably better to take your car to a garage rather than try to fix it yourself.

Mirrors, washers and wipers

Part of the MOT test when it comes to your windscreen is making sure that the driver has a clear view of the road. Anything that obstructs or hinders that view – like a malfunctioning wiper, or a big chip or crack, is likely to result in a minor or major fault. The condition of your mirrors and performance of your washers will also be tested, so make sure that all of these are up to the required standards.