What Can Fail My Car's MOT?

Understanding the most common reasons behind MOT failures can help you avoid the stress and cost of a retest.

Every year, countless cars fail their MOT tests due to issues that could have been easily prevented with a quick inspection or bit of maintenance.

Whether you’re getting ready for your first MOT, or you’ve been through it many times before, knowing what can cause a failure is essential for keeping your car roadworthy and legal.

In this guide, we’ll break down the most common MOT failures, what testers look for, and how to prepare your car in advance.

What is a Car MOT?

A car MOT (Ministry of Transport test) is a mandatory annual inspection for most vehicles over three years old in the UK.

The test ensures that your vehicle meets minimum safety and environmental standards to be driven legally on public roads.

Driving without a valid MOT certificate is illegal and can result in fines, penalty points, and even invalidated insurance in the event of an accident.

So it’s not just about ticking a legal box – it’s about ensuring your vehicle is safe to drive.

Top Reasons Why Cars Fail Their MOT

While many different faults can cause an MOT failure, there are some common culprits that appear time and time again.

While not limited to, the following are the most common factors of MOT failure:

1. Lights and indicators
2. Tyres and tread depth
3. Brakes
4. Windscreen, wipers, and washers
5. Suspension and steering
6. Exhaust and emissions
7. Number plates and vehicle identification

1. Lights and Indicators

Lights are one of the most frequent MOT failure points, often because of something as simple as a blown bulb.

The MOT checks include:

• Headlights (main beam and dipped)
• Brake lights
• Indicators (front, rear, and side repeaters)
• Number plate light
• Rear fog light (if fitted)
• Daytime running lights (for newer vehicles)

Make sure all your lights are working properly, lenses are clean and not cracked, and there’s no water ingress that could affect performance.

2. Tyres and Tread Depth

Tyres are essential for both safety and performance, and any issue here can lead to a failed MOT.

Your car's tyres must meet the legal minimum tread depth of 1.6mm across the central three-quarters of the tyre. They must also be free of cuts, bulges, or other visible damage.

Don’t forget to check the spare tyre if your vehicle carries one – some testers may inspect it depending on your vehicle’s configuration.

Learn how to check your tyre's tread depth by reading our tread depth check guide today.

3. Brakes

Brakes are critical to safety and undergo a thorough inspection during the MOT test.

The tester will check:

• Brake pads and discs for wear
• Brake fluid levels
• Handbrake function
• Any unusual noises or signs of imbalance during the rolling road test

If you’ve noticed reduced braking performance or noises when stopping, it’s worth getting them checked before your MOT.

4. Windscreen, Wipers, and Washers

You might not think your wipers can cause a failed MOT – but they can.

MOT testers will check that:

• Your windscreen is free from cracks or chips larger than 10mm in the driver's line of sight
• Wipers clear the windscreen effectively
• Screen wash jets function properly and spray correctly

Remember and top up your screen wash and replace worn wiper blades before the test.

5. Suspension and Steering

Uneven roads and potholes can take a toll on your suspension system, which is another leading cause of MOT failures.

The MOT checks for:

• Leaking or damaged shock absorbers
• Broken or corroded springs
• Excessive play or wear in steering components

If your car feels unstable, or you’ve heard clunking noises while driving, these could be signs of suspension issues worth addressing before test day.

6. Exhaust and Emissions

Your car’s exhaust system and emissions output must meet the legal standards for pollution.

The MOT tester will check:

• The exhaust system for leaks, noise levels, and secure fitting
• CO2 and other emissions using a gas analyser (for petrol or diesel engines)
• A warning light on your dashboard related to the engine or emissions can also result in a failure –  so don’t ignore it.

7. Number Plates and Vehicle Identification

Believe it or not, something as small as a dirty or incorrectly spaced number plate can cause a failure.

Make sure:

• Number plates are clean, clearly legible, and securely fixed
• Font and spacing comply with DVLA rules
• Your Vehicle Identification Number (VIN) is present and readable

How to Avoid a Failed MOT

The good news is many of these issues are avoidable with a quick pre-MOT check or minor maintenance.

A simple 10-minute inspection could save you the cost and hassle of a retest.

Here’s a quick pre-MOT checklist:

• Check all bulbs and replace any that are out
• Inspect tyre tread depth and sidewalls
• Make sure wipers are effective and washer fluid is topped up
• Test your horn, lights, and indicators
• Look under the car for any obvious leaks or damage

Final Thoughts

An MOT failure doesn’t have to be a surprise.

By staying aware of what can cause your car to fail and preparing in advance, you can pass your MOT the first time and stay road-legal without any added stress.

If your car does fail, don’t panic. The issues will be listed clearly, and a qualified garage can carry out any necessary repairs before a retest.

Staying on top of regular maintenance is key to keeping your vehicle roadworthy – not just for your MOT, but for everyday safety. A little preparation goes a long way.