Top Reasons Cars Fail Their MOT

The MOT test is a mandatory annual check that ensures your vehicle meets the minimum safety and environmental standards required to be roadworthy in the UK. It's a legal requirement for most vehicles over three years old, and failing it means you cannot drive your car until the necessary repairs are made.

Many MOT failures are entirely preventable with basic maintenance and routine checks. A quick inspection of key components ahead of your test can help avoid costly retests and ensure your vehicle is in good working order.

In this article, we'll explore the most common reasons cars fail their MOT, how to spot potential issues early, and what you can do to reduce your chances of failing.

Why MOT Failures Happen

Every year, around 30–40% of vehicles fail their MOT on the first attempt. While some of these are due to major faults, many are the result of minor issues that could easily be spotted and fixed in advance. It's also important to understand the distinction between a "major" failure and an "advisory" note. 

Major failures result in an automatic test failure and require immediate attention before the car can be driven again. Advisories, on the other hand, highlight items that may soon require repair or replacement but don't yet fail the vehicle. Regular maintenance and a simple pre-MOT check can make all the difference.

Top Reasons for MOT Failure

1. Faulty or Non-Working Lights

Lighting issues are among the top reasons vehicles fail their MOT. This includes not only headlights and brake lights, but also sidelights, indicators, reverse lights, fog lights, and number plate illumination. Testers check that all lights are working, correctly aligned, and emitting sufficient brightness. A misaligned headlight can dazzle oncoming drivers, while a broken brake light compromises safety. These are simple to check and fix at home, often requiring just a new bulb or fuse.

2. Tyre Issues

Tyres are crucial for road safety, and MOT testers inspect them for several criteria. Tread depth must meet the legal minimum of 1.6mm across the central three-quarters of the tyre, but anything close to this limit can still pose a safety risk. Testers also look for cracks, bulges, embedded objects, uneven wear, and signs of damage. Tyres that are under-inflated or over-inflated can impact braking and stability. Matching tyres on the same axle is also checked. Neglecting tyre condition not only risks an MOT failure but compromises safety on the road.

3. Brake Problems

Brake faults are one of the most serious reasons for failure, as they directly affect your ability to stop safely. MOT testers check brake pad and disc condition, fluid levels, and braking force through a rolling road test. Corroded or warped brake discs, worn pads, and contaminated or leaking fluid can all lead to failure. 

The vehicle must stop in a straight line and within a set distance. Unusual noises, dashboard warning lights, or pulling to one side while braking should be checked well before the MOT.

4. Suspension and Steering Faults

Suspension and steering systems play a critical role in handling, ride quality, and safety. Testers look for worn-out or broken springs, leaking shock absorbers, damaged ball joints, and any free play or stiffness in the steering. 

Drivers might not notice the gradual deterioration of these components, but they can make the vehicle unsafe. Uneven tyre wear, knocking sounds, or poor cornering are signs of trouble. These systems are more complex to check at home, so professional inspection is recommended if issues are suspected.

5. Visibility Issues

Clear visibility is essential, and testers inspect everything that might impair the driver’s view. Wiper blades must be effective at clearing the screen and free of splits or wear. Windscreen washers must spray adequately and consistently. 

Chips and cracks in the swept area—especially directly in front of the driver—can lead to failure if over 10mm in size. Rear-view and wing mirrors must be secure, free from damage, and provide clear views. Even items like stickers or dash-mounted devices can count against you if they obstruct visibility.

6. Number Plate and Registration Problems

Number plates must comply with legal standards for font, size, spacing, and visibility. MOT testers check that plates are securely attached, undamaged, and clearly readable. A dirty or cracked plate, or one with non-standard characters or spacing, will fail. 

Plates must also match the vehicle logbook. Personalised plates must still follow spacing and reflective rules. Making sure your plates are clean, legal, and securely fixed is a quick win before your test.

7. Exhaust and Emissions Problems

Excessive emissions or noise, damaged exhaust components, and visible smoke can result in failure. MOT testers inspect the system for leaks, corrosion, or insecure mounting. The exhaust must be sealed and quiet enough to meet legal limits. Emissions are tested based on fuel type and age of the vehicle. 

Diesels are particularly at risk of failing if fitted with a damaged or removed diesel particulate filter (DPF). Petrol cars may fail due to poor engine tuning or a faulty catalytic converter. Warning lights related to emissions systems must not be illuminated.

8. Windscreen Damage

The windscreen is critical for visibility and structural integrity. MOT testers focus on chips and cracks within the wiper’s swept area. Any damage over 10mm in this area—or 40mm outside it—is an instant fail. Even small chips can reflect light and obscure vision. 

Laminated screens may crack further if not repaired, so early intervention is key. Testers also check that the windscreen is secure, properly bonded, and free from delamination or other defects.

9. Fluid Leaks

Fluid leaks are a red flag for potential mechanical failure and environmental concerns. MOT testers look for leaks from brake lines, power steering systems, fuel tanks, coolant hoses, and engines. Brake fluid leaks are especially serious and can cause an immediate fail due to safety concerns. 

Oil leaks, while common in older vehicles, must not be excessive or dripping onto essential components. Parking on a clean, dry surface before your MOT can help reveal any leaking fluids.

10. Seatbelt and Restraint Issues

Seatbelts are vital for occupant safety and must be in excellent working condition. MOT testers check belt integrity, secure mounting, smooth retraction, and locking mechanism function. Fraying, cuts, or stretched belts are reasons for failure. Buckles must latch securely, and seat belt warning systems must work where fitted. 

Testers will also inspect child seat anchor points and airbag warning lights, which must not be illuminated. Ensuring your belts and restraint systems are fully functional is a straightforward but essential step before testing.

How to Reduce Your Risk of Failing

To reduce your risk of failing the MOT, it helps to do a basic check at home before your test. Inspect your lights, tyres, windscreen, wipers, and washer fluid. It’s also wise to book a full service ahead of your MOT, as a mechanic can spot underlying issues you might miss. Pay attention to any warning lights or strange sounds from your vehicle, and remember that regular maintenance throughout the year—not just before your test—will help keep your car roadworthy.

When to Get Help from Your Garage

If you're unsure about the condition of your car or want peace of mind before your MOT, booking a pre-MOT check with your local garage is a smart move. A trained technician can carry out a thorough inspection, diagnose hidden problems, and complete any necessary repairs quickly. 

Professional servicing not only increases your chances of passing the MOT first time but also helps extend the life of your vehicle and reduce the risk of future breakdowns.

Book Your Next MOT With Thurton Auto Centre

Most MOT failures are avoidable with a little preparation and awareness of what testers look for. Regular maintenance, routine checks, and addressing minor faults early can save time, stress, and unnecessary expense. A well-maintained vehicle is not only more likely to pass its MOT, but also safer and more reliable on the road.

If your MOT is approaching, whether for a car or motorhome, now is the ideal time to book a test or pre-check. At Thurton Auto Centre we offer MOT testing and support services to help ensure your vehicle meets the required standards. Book your MOT with us today and drive with confidence.