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Revealing the Most Frequent Causes of MOT Test Failures and How to Avoid Them


The MOT test is a critical annual assessment of a vehicle’s roadworthiness and safety. Without a valid MOT certificate, it is illegal to drive on public roads in the UK. Unfortunately, over 30% of vehicles fail their MOT test on the first attempt each year.

There are many different reasons an MOT test can result in failure. Everything from faulty brake lights to worn out tyres can lead to a fail outcome. Some defects are categorised as dangerous, meaning the car is deemed unroadworthy and should not be driven until fixed. Other failures are labeled as major or minor defects.

In this blog post, we will explore the most common causes of MOT failures. We’ll look at which vehicle components frequently show faults and defects during testing. We’ll also discuss the implications of different categories of failures, from minor to dangerous. Finally, we’ll provide helpful tips to avoid the most frequent pitfalls and pass your MOT test first time.

Understanding the reasons behind MOT failures empowers drivers to proactively maintain their vehicles. Simple checks and repairs done ahead of the test can prevent many issues. With the right preparation, drivers can improve road safety and feel confident their vehicle meets high standards.

Common Reasons for MOT Test Failures

One of the most frequent causes of MOT test failure are issues with the vehicle’s lighting system. Faulty bulbs account for around 17% of all MOT failures, with common problems including blown headlights, brake lights, indicators, or rear lights. Even minor defects like a faulty number plate light can cause a car to fail its MOT. Drivers are advised to thoroughly check all external lights before taking a test.

Worn or damaged tyres are another major reason for MOT failures, responsible for up to 30% of rejections. Tyres with cuts, bulges, or tread depth below the legal 1.6mm limit will result in a fail. Tyre issues can escalate quickly, so drivers should regularly inspect their tyres and replace any that are worn out. The AA recommends doing a simple 20p test, inserting a 20p coin into the main tread grooves, and if the outer band is obscured the tyre may be illegal.

Suspension faults account for around 7% of MOT failures. Knocking noises when driving over bumps, fluid leaks, or excessive corrosion of suspension components like shock absorbers will lead to a failure. Worn suspension jeopardises handling and braking, so worn parts should be replaced before the test.

MOT defects fall into three categories – dangerous, major and minor. Dangerous defects like faulty brakes mean the car is unroadworthy and illegal to drive until fixed. Major defects like oil leaks must be repaired before passing the MOT, while minor defects may pass but require attention. Driving an unroadworthy vehicle is illegal and extremely hazardous.

Most Common MOT Fails

  • Lights – 17%
  • Tyres – 30%
  • Suspension – 7%
  • Windscreen – 5%
  • Brakes – 6%

The Importance of Pre-MOT Checks

Performing thorough pre-MOT checks on your vehicle is one of the best ways to avoid test failure. By examining all lights, tires, fluid levels, and components ahead of time, you can identify and address any issues before the inspection.

Checking All Lights

Blown bulbs are the leading cause of MOT failures, accounting for up to 30% of all test failures. Before your test, do a walk-around of your car to check that all exterior lights are functioning – headlights, brake lights, turn signals, hazard lights, reverse lights, and fog lights. Have a friend watch as you turn signals on and off to catch any burnt out bulbs. Replacing any faulty bulbs beforehand can help you pass the lights portion of the MOT.

Enlisting Help

Asking a friend or family member to assist with your pre-MOT checks can be extremely beneficial. They can spot issues that you may miss on your own, like a brake light that has stopped working. Be sure to check all lights from various angles to ensure proper visibility. The second set of eyes helps verify that all required lights are operational.

Simplicity and Cost-Effectiveness of Bulb Replacement

Fixing minor electrical issues like blown bulbs is one of the simplest and most cost-effective repairs prior to an MOT test. Bulbs are inexpensive to purchase, usually between £2-£10 depending on the bulb type. Replacing them yourself takes just a few minutes, requiring no professional mechanical skills. This small investment of time and money can easily prevent the hassle and expense of having to get your car retested due to a failed indicator bulb.

Concerns over Proposed Two-Year Test Intervals

The UK government has recently proposed extending the gap between MOT tests from one year to two years for cars over three years old. This suggestion has been met with strong opposition from the motor industry due to concerns over road safety.

Increased Risks of Critical Component Failure

Industry experts argue that doubling the time between MOTs significantly increases the risks of critical vehicle components like brakes and tyres degrading to dangerous levels. These safety-critical parts naturally wear down through regular use, so yearly inspections help identify problems before they lead to accidents.

More Frequent Breakdowns

Data shows a considerable rise in breakdowns among cars over 3 years old compared to newer vehicles. Less frequent MOTs would likely worsen this trend as minor defects go undetected for longer, eventually causing more major mechanical problems.

Long-Term Cost Increases

Though less frequent MOTs seem to save money in the short-term, the potential for more serious issues down the line can prove more costly. Catching minor faults early is more affordable than major repairs after critical failures. This may erase any savings from biennial tests.

Strong Public Opposition

Surveys indicate most drivers oppose less frequent MOTs. 76% said annual tests should be maintained, while just 22% supported biennial testing. The public clearly prioritises road safety over small potential savings.

Expert Warnings Over Road Safety Impacts

Industry bodies like the IGA warn biennial MOTs will compromise road safety standards. They argue the current yearly inspection regimen has been pivotal in maintaining the UK’s high road safety levels by catching dangerous defects.

In summary, there are compelling concerns from experts and the public that switching to two-year MOT intervals would significantly undermine road safety for little gain. The evidence strongly suggests maintaining annual tests as the responsible choice.


Regular MOT testing is vital for keeping vehicles roadworthy and drivers safe. As we’ve seen, many common MOT failures like blown bulbs, worn tyres, and obscured vision can be easily avoided with basic maintenance and pre-MOT checks.

However, there are valid concerns that extending MOT test intervals from one year to two could lead to more unroadworthy vehicles and potential increases in accidents. Many drivers oppose this proposed change, and industry experts have warned it could negatively impact road safety.

The best way to maximise your chances of sailing through the MOT is to be proactive. Check all lights and replace any blown bulbs. Inspect tyres for damage and ensure tread depth is above the legal limit. Top up screenwash, replace wipers if needed, and remove any items blocking your vision. And consider having a pre-MOT check done by a professional mechanic.

By understanding common MOT failure causes and taking preventative action, you can help keep your vehicle in a safe, roadworthy condition. Together we can work to oppose any changes that could compromise road safety in the years

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