Why Your Car Might Fail its MOT Test

The MOT test is a crucial annual check for vehicles over three years old in the UK, designed to ensure they are roadworthy and meet environmental standards. Failing this test can be a frustrating and costly experience, but understanding the common reasons for failure can help you prepare and prevent it. This article delves into the most frequent culprits that lead to an MOT test failure, empowering you with the knowledge to keep your vehicle compliant and safe.

Understanding the MOT Test Categories

Before diving into specific failure points, it's important to understand how the MOT test categorises issues. Vehicles are assessed in several key areas, and problems are classified as either 'minor', 'major', or 'dangerous'.

• Minor: Defects that are not expected to cause danger but should be repaired as soon as possible.
• Major: Defects that could cause danger to yourself, others, or the environment. Your vehicle will fail the MOT test if it has any major defects.
• Dangerous: Defects that pose a direct and immediate risk to road safety or have a serious impact on the environment. Your vehicle will fail the MOT test immediately if it has any dangerous defects.

Any vehicle that fails will receive a refusal of an MOT test certificate and will need to be repaired. For dangerous defects, you cannot drive the vehicle until it has been repaired.

Top Reasons for MOT Test Failures

While the MOT test covers a wide range of checks, certain areas consistently contribute to a significant number of failures. Here are the most common:

1. Lighting and Signalling Equipment

This is a perennial favourite for MOT failures. It's not just about having all lights working; it's also about them being correctly aimed and the correct colour.

• Headlights: Incorrect aim (too high or too low), faulty bulbs, or damaged casings.
• Brake Lights: Not illuminating when the brake pedal is pressed, or being permanently on.
• Indicator Lights: Not flashing, flashing too fast, or showing the wrong colour.
• Number Plate Lights: Not illuminating the rear number plate correctly.
• Reflectors: Missing or damaged rear reflectors.

Tip: Regularly check all your lights, including brake lights when someone else presses the pedal, and ensure they are clean and undamaged.

2. Brakes

The braking system is paramount for safety, and any issues here will result in a fail. This covers the performance, condition, and operation of the braking system.

• Brake Performance: Insufficient braking efficiency on either the service brake or the parking brake. This is often detected during the roller test.
• Brake Fluid: Low brake fluid levels or contamination.
• Brake Lines: Corroded, leaking, or damaged brake lines and hoses.
• Brake Discs and Pads: Worn brake discs (below minimum thickness) or pads, or discs/pads that are cracked or excessively scored.
• Parking Brake: Ineffective parking brake, or a parking brake that binds or fails to release properly.

Tip: Listen for any unusual noises when braking, and if you notice a spongy brake pedal or the car pulling to one side when braking, get it checked immediately.

3. Tyres

Tyres are your car's only contact with the road, so their condition is critical. The MOT test checks for tread depth, damage, and correct fitment.

• Tread Depth: Tyres must have a minimum tread depth of 1.6mm across the central three-quarters of the breadth of the tread.
• Tyre Damage: Cuts, bulges, or exposed cords on the tyre sidewall or tread.
• Incorrect Fitment: Tyres that are the wrong size or type for the vehicle, or mismatched tyres on the same axle (unless they are identical).
• General Condition: Tyres that are deflated or showing signs of excessive wear and tear.

Tip: Regularly check your tyre pressure and tread depth. You can use a tyre tread depth gauge or a 20p coin – if you can see the Queen's head when inserted into the tread, it's time for new tyres.

4. Steering and Suspension

Problems with steering and suspension can significantly affect a vehicle's handling and safety.

• Steering: Excessive play in the steering wheel, worn steering rack, or damaged steering components.
• Suspension: Worn or damaged suspension components such as shock absorbers, springs, or ball joints. Leaking shock absorbers are also a common failure point.
• Wheel Bearings: Worn wheel bearings that exhibit excessive play.

Tip: If you notice your car pulling to one side, excessive vibration through the steering wheel, or a 'clunking' noise when going over bumps, these could be signs of suspension or steering issues.

5. Exhaust Emissions

This is a major category, especially for modern vehicles. The test ensures your car meets current environmental standards for exhaust emissions.

• Excessive Smoke: The exhaust system emitting visible smoke of an inappropriate colour (blue, black, or white) or density.
• High CO2 Levels: For petrol engines, the carbon monoxide (CO) levels may be too high.
• High Hydrocarbon Levels: For both petrol and diesel engines, excessive unburnt hydrocarbons can indicate combustion problems.
• Diesel Particulate Filter (DPF): For diesel vehicles, a missing or faulty DPF will cause a failure. Tampering with or removing a DPF is illegal.
• Catalytic Converter: A faulty or missing catalytic converter can lead to increased emissions.

Tip: If your car has been suffering from poor performance or has had starting issues, it could be a sign that the exhaust system or catalytic converter is not functioning correctly. Regular servicing can help identify these problems early.

6. Windscreen and Wipers

While seemingly minor, these components are crucial for visibility and driver safety.

• Windscreen: Cracks or chips in the windscreen that are larger than 10mm in the driver's direct line of sight, or larger than 40mm elsewhere.
• Wipers: Wipers that do not clear the windscreen effectively or are damaged.
• Washers: Windscreen washers that are not working, meaning you cannot clear the windscreen of dirt or spray.

Tip: Keep your windscreen clean and check your wiper blades for wear and tear. Small chips can often be repaired before they spread.

7. Body, Structure, and Chassis

The structural integrity of the vehicle is assessed for corrosion and damage.

• Corrosion: Significant corrosion to the vehicle's structure, chassis, or suspension mounting points.
• Damage: Any damage that compromises the structural integrity or could cause injury.
• Doors: Doors that do not open, close, or stay open correctly.
• Seatbelts: Faulty seatbelt mechanisms, frayed webbing, or missing seatbelts.

Tip: Keep an eye on areas prone to rust, especially around wheel arches and sills. Regularly check that all doors open and close smoothly and that seatbelts retract and lock correctly.

8. Other Common Failure Points

Beyond the major categories, several other items can lead to an MOT failure:

• Horn: A horn that does not sound or is not audible.
• Fuel System: Leaks in the fuel system.
• Oil Leaks: Excessive oil leaks that could pose a hazard.
• Speedometer: A malfunctioning speedometer.
• Engine Warning Lights: While not always a direct fail, if the engine management light is on and indicates a serious issue, it may lead to a fail.

Preparing Your Vehicle for the MOT Test

The best way to avoid an MOT failure is to be proactive with your vehicle's maintenance. Regular servicing, as recommended by the manufacturer, will help identify and rectify potential issues before they become serious enough to cause a fail.

Pre-MOT Checks

Before taking your car for its MOT, consider performing some basic checks yourself:

• Check all lights are working and clean.
• Inspect tyres for tread depth and damage.
• Check wiper blades and windscreen washer fluid.
• Ensure all seatbelts are present and functioning correctly.
• Check for any obvious fluid leaks under the car.
• Listen for any unusual noises from the engine, brakes, or suspension.

What Happens After a Failure?

If your vehicle fails its MOT, you will be given a 'refusal of an MOT test certificate' document which details the reasons for failure. You will then need to get the necessary repairs carried out. Depending on the severity of the defects, you may be able to drive your car to a pre-arranged repair appointment. However, if there are 'dangerous' defects, you cannot legally drive the vehicle on the road until it has been repaired and re-tested.

Re-testing Your Vehicle

After repairs, your vehicle will need to be re-tested. If you have the repairs done at the same test centre, a partial re-test might be free or cheaper. If you take it elsewhere, it will be a full MOT test again.

Conclusion

An MOT test failure can be avoided with a little foresight and regular maintenance. By understanding the common reasons for failure, performing basic checks, and addressing any emerging issues promptly, you can significantly increase your chances of passing the MOT test and ensure your vehicle remains safe and legal on UK roads. Don't wait for the MOT to be your first indication of a problem; maintain your car diligently.

Frequently Asked Questions (FAQs)

Q1: Can I drive my car if it fails its MOT?

You can drive your car if it fails its MOT, provided the existing MOT certificate has not expired and the failure does not involve 'dangerous' defects. If there are dangerous defects, you cannot drive the vehicle until it is repaired.

Q2: How long do I have to get repairs done after failing an MOT?

There is no strict time limit for completing repairs, but you cannot legally drive the vehicle on public roads if it has dangerous defects or if its MOT has expired.

Q3: What is the most common reason for an MOT failure?

Lighting and signalling equipment, along with tyres and brakes, are consistently among the most common reasons for MOT test failures.

Q4: Does a flat tyre cause an MOT failure?

Yes, a flat tyre, or any tyre that is significantly under-inflated or damaged, will cause an MOT failure.

Q5: What if my car fails the emissions test?

If your car fails the emissions test, it indicates that your exhaust emissions are too high. This often points to issues with the engine, catalytic converter, or exhaust system. You will need to have these components checked and repaired before the car can pass its MOT.

Q6: Can I get an MOT done at any garage?

No, only government-authorised MOT test centres can carry out MOT tests. You can find an authorised centre on the GOV.UK website.