MOT Failures: Common Reasons

Understanding Common MOT Test Failures

The annual MOT test is a legal requirement for most vehicles over three years old in the UK. Its primary purpose is to ensure that vehicles on our roads are safe, environmentally sound, and meet the minimum legal standards. While many drivers prepare diligently, a surprising number of vehicles fail their MOT each year. Understanding the most common reasons for these failures can help you prepare your car and avoid the inconvenience and potential cost of a re-test.

The MOT test covers a wide range of checks, from the obvious like brakes and tyres to less visible components like emissions and lighting. Failures can range from minor issues that are easily rectified to more serious problems that could compromise safety. This guide will delve into the most frequent culprits behind an MOT failure, offering insights into what inspectors are looking for and how you can ensure your vehicle is in tip-top condition.

Tyres: The Foundation of Safety

Tyres are arguably one of the most critical safety components on any vehicle. They are the only point of contact between your car and the road, influencing grip, braking, and steering. It's no surprise, then, that tyres are a very common reason for MOT failures.

• Tread Depth: The legal minimum tread depth for car tyres in the UK is 1.6mm across the central three-quarters of the tyre's breadth. Any less, and it's an automatic fail. Inspectors will check the entire circumference and breadth of the tyre.
• Damage: Cuts, cracks, bulges, or exposed internal structure on the tyre sidewall or tread are all reasons for failure. Even minor damage can compromise the tyre's integrity.
• Incorrect Fitment: Tyres must be the correct size and type for your vehicle as specified by the manufacturer. Mixing radial and cross-ply tyres on the same axle is also prohibited.
• Under-inflation/Over-inflation: While not always a direct MOT failure point unless it causes visible damage or affects performance, severely incorrect tyre pressures can lead to uneven wear and compromised handling, which might be picked up during the test.

Pro Tip: Regularly check your tyre tread depth using a tyre tread depth gauge or a 20p coin. Insert the coin into the deepest groove; if the outer band of the 20p coin is visible, your tread is below the legal limit.

Braking System: Your Lifeline

The braking system is paramount for safety. Any issue that affects its performance or efficiency will result in an MOT failure.

• Worn Brake Pads/Discs: Insufficient material on brake pads or excessively worn or grooved brake discs are common reasons for failure.
• Brake Fluid: Low brake fluid levels or contaminated fluid can significantly impact braking performance. The MOT test also checks for leaks within the brake system.
• Brake Performance: The test includes a roller brake test to measure the efficiency of the braking system. If the brakes are unbalanced between wheels on the same axle, or if they don't meet the required stopping power, the vehicle will fail.
• Handbrake: The handbrake (parking brake) must hold the vehicle securely on a gradient. If it fails to do so during the test, it's a fail.

Key Component: Brake fluid should ideally be changed every two years as it absorbs moisture, which can reduce its effectiveness and lead to corrosion.

Lights: Visibility is Crucial

All lights on your vehicle must be in working order, the correct colour, and securely fitted. Faulty or missing lights are a frequent cause of MOT failure.

• Non-functioning Lights: Headlights (dipped and main beam), taillights, brake lights, indicators, and fog lights must all illuminate correctly.
• Incorrect Colour: Headlights should emit white light, rear fog lights red, and brake lights red. Indicators can be amber or yellow. Any deviation from these colours is a fail.
• Misaligned Headlights: Headlights that are aimed too high or too low can dazzle oncoming drivers or fail to illuminate the road effectively. The beam pattern is checked during the test.
• Cracked or Missing Lenses: Damaged light lenses can obscure the light or cause it to scatter, leading to a failure.

Suspension: For a Smooth Ride

The suspension system is vital for a comfortable and safe ride, affecting handling and tyre contact with the road.

• Worn Shock Absorbers: Leaking or excessively worn shock absorbers will result in a fail.
• Damaged Springs: Cracked or broken suspension springs are a significant safety hazard and an immediate reason for failure.
• Loose or Damaged Components: Any worn or loose suspension joints, bushes, or links can lead to instability and are grounds for failure.

Exhaust Emissions: Environmental Impact

Modern vehicles have strict emissions standards to meet. The MOT test checks that your car's emissions are within the legal limits for its age and fuel type.

• High CO2 Emissions: If your car emits more carbon monoxide (CO) than permitted for its engine type, it will fail.
• Other Pollutants: The test also checks for other harmful emissions like hydrocarbons (HC) and particulates.
• Visible Smoke: Excessive smoke from the exhaust, regardless of colour, can indicate an engine problem and lead to a failure.
• Catalytic Converter: A missing or faulty catalytic converter will cause emissions to be too high.

Important Note: Ensure your vehicle has had a recent service, especially if it’s older, as issues like worn spark plugs or a clogged air filter can contribute to increased emissions.

Visibility: Seeing and Being Seen

Clear visibility is crucial for safe driving.

• Windscreen: Damage to the windscreen in the driver's direct line of sight (the area swept by the wipers) that is larger than 10mm or any damage larger than 40mm outside this area will result in a fail.
• Wipers and Washers: Wipers must clear the windscreen effectively, and the washers must provide an adequate supply of washer fluid.
• Mirrors: All mirrors must be securely fitted and in good condition.

Bodywork and Structure: The Integrity of Your Car

The structural integrity of your vehicle is assessed to ensure it's safe to drive.

• Corrosion: Significant corrosion in critical areas, such as around suspension mounting points, the chassis, or structural members, is a fail. Small areas of surface rust are generally acceptable.
• Sharp Edges: Sharp or protruding parts that could injure pedestrians or other road users are prohibited.
• Doors: Doors must open and close correctly from both the inside and outside.
• Seatbelts: Seatbelts must be present, in good condition, and function correctly, including the locking mechanism.

Other Common Failures

Beyond the major categories, several other issues frequently cause MOT failures:

• Horn: The horn must be present and in working order.
• Fuel System: Leaks from the fuel system are a serious safety concern and will lead to a fail.
• Engine Warning Lights: If the engine management warning light is illuminated, the vehicle may fail, particularly if it indicates a serious fault.
• Steering: Worn steering components, excessive play in the steering wheel, or damaged steering racks are all reasons for failure.

Preparing for Your MOT: A Checklist

To maximise your chances of passing your MOT first time, consider the following checks before your appointment:

Frequently Asked Questions

Q1: What happens if my car fails its MOT?

A1: If your car fails, you will be given a refusal certificate. You can still drive your car if the existing MOT is valid and the new failure does not result in dangerous defects. You will need to have the necessary repairs carried out and then have the vehicle re-tested. If the repairs are done at the same test centre, a partial re-test might be free or at a reduced cost.

Q2: Can I drive my car if it has dangerous defects?

A2: No, you cannot drive your car if it has dangerous defects identified during the MOT test. Driving a vehicle with dangerous defects can lead to prosecution.

Q3: How much does an MOT cost?

A3: The maximum fee for an MOT test is set by the government. For cars, it's currently £54.85. Prices can vary between test centres, but they cannot charge more than the maximum fee.

Q4: What is the difference between a minor, major, and dangerous defect?

A4: Minor defects should be repaired as soon as possible but are not immediate reasons for failure. Major defects are defects that are likely to affect the safety of the vehicle or are not in conformity with the regulations. They will result in a failure. Dangerous defects are defects that could cause serious or fatal injury. A vehicle with dangerous defects must not be driven on the road.

Conclusion

The MOT test is a vital part of ensuring road safety in the UK. By understanding the most common reasons for failure, particularly concerning tyres, brakes, lights, emissions, and structural integrity, you can proactively maintain your vehicle. Regular checks and addressing minor issues before they become major problems will not only help your car pass its MOT smoothly but also contribute to its overall longevity and your safety on the road. Don't wait until the last minute; stay on top of your vehicle's maintenance to avoid unexpected failures and costly repairs.

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