Top 10 Common Reasons Cars Fail Their MOT

Understanding the most common reasons for MOT failures can save you time, money, and frustration. With approximately 29% of the 8.4 million vehicles tested annually failing their initial MOT examination, knowing what problems to look for and address proactively is invaluable knowledge for every UK driver.

The Driver and Vehicle Standards Agency (DVSA) publishes detailed statistics about MOT test results, revealing consistent patterns in failure reasons. The good news is that many of the most common MOT failures are preventable through regular maintenance and simple pre-test checks.

This guide examines the top 10 most common reasons for MOT failures based on official DVSA statistics, explaining why these problems occur, how to identify them, and what you can do to prevent them.

1. Lighting and Signalling Defects (18.9% of failures)

Lighting defects consistently rank as the number one cause of MOT failures, yet many of these problems are easily preventable with regular checks.

Common Problems:

• Blown bulbs in headlights, tail lights, brake lights, or indicators
• Headlight misalignment causing poor light distribution
• Damaged or clouded light lenses reducing light output
• Faulty electrical connections causing intermittent operation
• Incorrect bulb types or non-standard modifications

Prevention Tips: Check all lights weekly, including headlights (main and dipped beam), tail lights, brake lights, indicators, hazard warning lights, and number plate lights. Have someone help you test brake lights and indicators, or use reflective surfaces to check operation.

Replace blown bulbs immediately and ensure you’re using the correct bulb types specified by your vehicle manufacturer. Clean light lenses regularly and address any cracks or damage promptly.

Typical Repair Costs: £5-50 for bulb replacement, £30-100 for headlight alignment, £50-200 for lens replacement.

2. Suspension Component Failures (13.4% of failures)

Suspension system defects are the second most common cause of MOT failures, affecting vehicle safety, handling, and tyre wear.

Common Problems:

• Worn shock absorbers or struts leaking fluid
• Damaged suspension bushes causing excessive movement
• Broken or cracked coil springs
• Worn ball joints or track rod ends with excessive play
• Damaged anti-roll bar components

Prevention Tips: Listen for unusual noises when driving over bumps or turning corners. Check for oil leaks around shock absorbers and look for uneven tyre wear patterns that might indicate suspension problems.

Have suspension components inspected during regular services and address any developing problems promptly before they become serious enough to cause MOT failure.

Typical Repair Costs: £100-300 per shock absorber, £50-150 for bushes, £150-400 for springs, £80-200 for ball joints.

3. Brake System Issues (10.3% of failures)

Brake system defects represent serious safety concerns and are treated with utmost seriousness during MOT testing.

Common Problems:

• Worn brake pads or shoes below minimum thickness
• Damaged or excessively worn brake discs or drums
• Brake fluid leaks from calipers, cylinders, or pipes
• Corroded brake pipes or damaged brake hoses
• Poor handbrake adjustment or operation

Prevention Tips: Monitor brake pedal feel and listen for unusual noises during braking. Check brake fluid levels regularly and look for any signs of leakage around wheels or under the vehicle.

Have brakes inspected annually and replace worn components before they reach minimum thickness limits. Address any brake problems immediately as they represent serious safety hazards.

Typical Repair Costs: £80-200 for brake pads, £150-400 for brake discs, £100-300 for brake fluid system repairs.

4. Tyre Condition and Safety (7.8% of failures)

Tyre-related defects are easily preventable but remain a common cause of MOT failures due to inadequate maintenance and inspection.

Common Problems:

• Insufficient tread depth below the legal minimum of 1.6mm
• Cuts, bulges, or exposed cords indicating structural damage
• Incorrect tyre sizes or mixing different tyre types
• Damaged or corroded wheels affecting tyre mounting

Prevention Tips: Check tyre tread depth monthly using a tread depth gauge or the 20p coin test. Inspect tyres for damage, including cuts, bulges, or embedded objects.

Maintain correct tyre pressures and rotate tyres regularly to ensure even wear. Replace tyres before they reach the legal minimum tread depth to maintain optimal safety and performance.

Typical Repair Costs: £50-150 per tyre depending on size and quality, £100-300 for wheel repairs.

5. Exhaust System Problems (6.2% of failures)

Exhaust system defects include both physical damage and emissions failures, affecting both safety and environmental compliance.

Common Problems:

• Excessive emissions exceeding legal limits
• Holes, cracks, or corrosion in exhaust pipes or silencers
• Damaged or contaminated catalytic converters
• Loose or missing exhaust mounting brackets
• Failed diesel particulate filters (DPF)

Prevention Tips: Have emissions systems serviced regularly and use quality fuel to maintain clean combustion. Address any exhaust smoke, unusual smells, or increased noise levels promptly.

Avoid short journeys that prevent proper exhaust system operation, particularly for diesel vehicles with DPF systems that require regular regeneration cycles.

Typical Repair Costs: £50-200 for exhaust repairs, £300-1,500 for catalytic converter replacement, £1,000-3,000 for DPF replacement.

6. Steering System Defects (5.1% of failures)

Steering system problems can seriously affect vehicle control and safety, making them a priority during MOT testing.

Common Problems:

• Excessive play in steering wheel or steering components
• Power steering fluid leaks or pump failures
• Worn steering rack or pinion components
• Damaged track rod ends or ball joints
• Steering wheel misalignment

Prevention Tips: Monitor steering feel and responsiveness, noting any changes in steering effort or precision. Check power steering fluid levels and look for leaks around steering components.

Have wheel alignment checked if the vehicle pulls to one side or if the steering wheel isn’t centered when driving straight.

Typical Repair Costs: £100-400 for steering component replacement, £50-150 for power steering repairs, £50-100 for wheel alignment.

7. Body Structure and Corrosion (4.7% of failures)

Structural problems can range from minor corrosion to serious safety concerns affecting vehicle integrity.

Common Problems:

• Corrosion affecting safety-critical areas like seat belt mounting points
• Damaged sills or floor panels compromising structural strength
• Faulty door or tailgate operation affecting safety
• Windscreen damage within the driver’s line of sight
• Insecure seat or seat belt mountings

Prevention Tips: Inspect your vehicle regularly for signs of corrosion, particularly around wheel arches, door frames, and sill areas. Address minor rust spots before they develop into serious structural problems.

Keep drainage holes clear to prevent water accumulation and accelerated corrosion. Consider professional rust treatment for older vehicles in high-risk areas.

Typical Repair Costs: £200-1,000 for minor structural repairs, £500-2,000+ for major bodywork.

8. Electrical System Faults (3.9% of failures)

Modern vehicles rely heavily on electrical systems, making electrical reliability increasingly important for MOT compliance.

Common Problems:

• Battery or charging system problems affecting system operation
• Damaged wiring harnesses causing system failures
• Faulty electronic control units (ECUs)
• Failed sensors affecting safety or emissions systems
• Warning lights indicating system malfunctions

Prevention Tips: Address warning lights promptly and have electrical problems diagnosed professionally. Maintain battery terminals clean and secure, and replace aging batteries before they fail completely.

Protect wiring from damage and have electrical systems checked during regular services.

Typical Repair Costs: £50-150 for battery replacement, £100-500 for electrical repairs, £200-800 for ECU problems.

9. Fuel System Issues (2.8% of failures)

Fuel system problems primarily involve safety concerns related to fuel containment and delivery.

Common Problems:

• Fuel tank corrosion or damage causing leaks
• Damaged fuel lines or loose connections
• Faulty or missing fuel caps affecting emissions
• Fuel pump or delivery system problems

Prevention Tips: Check for fuel odours that might indicate leaks and ensure the fuel cap seals properly. Have fuel system components inspected during regular services.

Address any fuel delivery problems promptly as they can affect engine performance and emissions.

Typical Repair Costs: £100-500 for fuel system repairs, £300-800 for fuel tank replacement.

10. Windscreen Wipers and Washers (2.3% of failures)

While seemingly minor, wiper and washer systems are essential for maintaining driver visibility and are therefore tested during MOT examinations.

Common Problems:

• Worn, damaged, or missing wiper blades
• Failed wiper motors or damaged linkages
• Empty washer fluid reservoirs or blocked jets
• Inoperative rear wiper systems were fitted

Prevention Tips: Replace wiper blades annually or when they show signs of wear. Keep washer fluid reservoirs topped up and clear blocked jets promptly.

Test wiper and washer operation regularly, particularly before winter weather when visibility systems are most critical.

Typical Repair Costs: £10-30 for wiper blades, £50-150 for wiper motor repairs, £20-50 for washer system repairs.

Prevention Strategies

Regular Maintenance

The most effective way to avoid MOT failures is through regular maintenance and prompt attention to developing problems. Many failures result from neglecting basic maintenance tasks that could prevent more serious problems.

Establish a regular inspection routine covering lights, tyres, fluid levels, and basic system operation. Address minor problems before they develop into MOT failure points.

Pre-MOT Inspections

Consider having a professional pre-MOT inspection performed several weeks before your test is due. These inspections identify potential problems without the legal implications of an official test, giving you time to address issues at your convenience.

When you need comprehensive MOT testing, choose a reputable test centre that offers thorough examination and professional advice about addressing any problems identified.

Professional Servicing

Regular professional servicing helps identify and address potential MOT failure points before they become serious. Qualified technicians can spot developing problems and recommend preventive maintenance that saves money in the long term.

Conclusion

Understanding the most common MOT failure reasons empowers vehicle owners to take proactive steps to maintain their vehicles and avoid test failures. The top 10 failure categories outlined here account for the vast majority of MOT failures, and many can be prevented through regular maintenance and simple checks.

The consistency of these failure patterns demonstrates that basic maintenance practices remain crucial regardless of advancing vehicle technology. Regular attention to lights, tyres, brakes, and other fundamental systems can significantly improve your chances of passing your MOT test first time.

Prevention is always more cost-effective than repair, and the financial benefits of avoiding MOT failures extend beyond retest fees to include preventing more serious problems that could develop if minor issues are ignored.