What are the Most Common Reasons for MOT Failure?

car mot failures

As a motorist, there are various responsibilities you are expected to adopt, from paying road tax to obtaining insurance coverage and beyond. But perhaps the most important obligation you have is to take your car in for an annual MOT.

Any car that has been on the road for more than three years is eligible for an MOT – and without an MOT certificate, your car cannot legally be driven on UK roads. There are special exemptions for cars that are over 40 years old, but MOTs are nonetheless a requirement for the vast majority of motorists. If your current MOT is near expiry, or your new car is approaching its fourth year on UK roads, you should book your MOT online before you incur a fine.

An MOT is a comprehensive test, that examines the key functions and conditions of each car. Your car’s parts and mechanisms are judged using a three-tier ‘defect’ system, as problems and issues represent ‘minor’, ‘major’ or ‘dangerous’ defects. Complex as the test rubric is, the results are simple: a single major or dangerous defect results in an MOT failure. But what are the most common causes of MOT failure?

Lights and Lamps

The single most common cause of MOT failure amongst motorists is attributed to lights and indicator lamps. According to government MOT test data from 2022, over a quarter of all vehicle defects reported were related to lamps, reflectors and electrical equipment.

There is a number of ways in which lighting and electronics can result in you failing your MOT. Broken or missing headlights or indicator lamps are an immediate fail, as are installed headlight reflectors – which are used to redirect headlights for driving in Europe.

There are also fail conditions relating to the warning lights on your driver-side dash. These lights are meant to indicate a major issue with your car, and should cause you to visit a service mechanic immediately. If any warning lights are lit during your MOT, your car will fail – even if they are lit as a result of an electrical issue.


Tyres are another extremely common cause of MOT failure, being an ancillary part of a vehicle often forgotten about by motorists. Tyres are only road legal if they have a tread depth above 1.6mm. Checking tyres before you book your next MOT could save you the cost of a re-test, and the marked-up price of tyres from your local test centre.


According to government data, brake defects make up more than 16% of all reported defects. These may be a result of low or non-existent brake fluids, worn brake pads or discs, or even mechanical failure of the brakes altogether. This can be difficult to avoid for motorists, especially those who own older cars – but checking fluids is a strong way to avoid unnecessary failure.

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