Key takeaway: Around 36% of all cars fail their MOT on the first attempt in the UK. The top five failure reasons (lighting, tyres, suspension, brakes and driver's view) account for over 70% of all failures. Most of these can be checked and fixed at home for under £100 before your test, saving you a retest fee and the inconvenience of a second visit.
The MOT test is an annual safety inspection required for all cars over three years old in the UK. It costs a maximum of £54.85 (the DVSA cap), though many garages charge less. Failing means your car cannot legally be driven on public roads (except to a pre-booked MOT appointment or repair garage) until the faults are fixed and the car passes a retest.
In this guide, we break down the most common failure categories using real DVSA data, explain what you can check yourself before the test, and estimate the typical repair costs for each issue. If you want to see the full MOT history for any specific car, enter the registration number in our free tool. You will see every test result, advisory, and failure going back to the car's first MOT.
MOT Failure Rates: The Big Picture
According to DVSA data, approximately 36% of cars fail their MOT on the first attempt. That means more than one in three cars has at least one defect serious enough to fail. The failure rate increases with the age of the car:
| Car Age | Approximate Fail Rate |
|---|---|
| 3 years (first MOT) | 15-20% |
| 5 years | 25-30% |
| 7 years | 35-40% |
| 10 years | 40-50% |
| 15+ years | 50-60% |
The 10 Most Common MOT Failure Reasons
1. Lighting and Signalling (30% of all failures)
Lighting faults are the single most common reason for MOT failure, and also one of the easiest to fix. Common issues include:
- Blown bulbs: Headlights, brake lights, indicators, fog lights, number plate lights. Walk around your car with the engine running and all lights activated. Ask someone to press the brakes while you check the rear. Cost to fix: £5 to £30 for most bulbs, DIY in minutes.
- Headlight aim: Headlights must be aimed correctly. If you have replaced a headlight unit or the car has been in an accident, they may be misaligned. Cost to fix: £20 to £40 at a garage.
- Cracked or yellowed lenses: Damaged headlight lenses can reduce light output below the required level. Replacement lens: £30 to £150. Polishing kit for yellowed lenses: £10 to £20.
2. Tyres (18% of all failures)
Tyre failures come in several forms:
- Tread depth: The legal minimum is 1.6mm across the central three-quarters of the tyre. Check with a 20p coin: if the outer band of the coin is visible when inserted into the tread, the tyre is below the legal limit. Cost: £50 to £120 per tyre depending on size.
- Damage: Cuts, bulges, exposed cords. Any visible structural damage is an automatic fail. Cost: tyre replacement (£50 to £120).
- Mismatched tyres: Different tyre sizes on the same axle will fail. Check that both front tyres match and both rear tyres match.
3. Suspension (13% of all failures)
Suspension components wear out gradually, so you may not notice until the MOT tester checks. Common failures:
- Worn shock absorbers: Bounce each corner of the car and release. It should settle within one or two bounces. More than that indicates worn dampers. Cost: £150 to £400 per pair fitted.
- Worn ball joints and bushes: These cause knocking sounds over bumps. Cost: £80 to £250 per corner.
- Anti-roll bar links and bushes: Very common failure point. Cost: £50 to £150 per side.
- Broken coil springs: Particularly common in UK cars due to potholes. Cost: £100 to £250 per spring fitted.
4. Brakes (12% of all failures)
- Worn brake pads: Pads below the minimum thickness will fail. Cost: £80 to £180 per axle fitted.
- Worn or corroded brake discs: Discs with deep scoring, cracks, or excessive lip will fail. Cost: £120 to £300 per axle for discs and pads together.
- Brake fluid contamination: Brake fluid absorbs moisture over time, reducing its boiling point. A fluid change costs £40 to £80.
- Parking brake: The handbrake must hold the car on a slope. Adjustment or cable replacement: £50 to £200.
5. Driver's View of the Road (8% of all failures)
- Windscreen damage: A chip or crack larger than 10mm in the driver's swept area (zone A) will fail. Larger than 40mm anywhere in the swept area will also fail. Cost: chip repair £30 to £70, full windscreen replacement £150 to £400.
- Wiper blades: Worn or damaged wiper blades that do not clear the windscreen properly will fail. Cost: £10 to £30 for a new pair.
- Washer fluid: An empty washer bottle is a fail. Cost: £2 for a bottle of screenwash.
6. Exhaust and Emissions (7% of all failures)
- Emissions above limit: Petrol cars are tested at idle and at fast idle. Diesel cars undergo a smoke opacity test. A failing catalytic converter or diesel particulate filter (DPF) is the usual culprit. Cost: cat replacement £300 to £1,200, DPF cleaning £200 to £400.
- Exhaust leaks: Holes, corrosion, or loose connections in the exhaust system. Cost: £80 to £300 depending on the section affected.
7. Steering (5% of all failures)
- Excessive play in the steering: Worn track rod ends and steering rack bushes are the usual cause. Cost: £80 to £200 per track rod end, £300 to £600 for a steering rack.
- Power steering fluid leaks: Visible leaks from the steering system will fail. Cost: £50 to £200 depending on the leak source.
8. Body and Structure (3% of all failures)
- Corrosion: Rust within 30cm of a structural point (subframe mount, suspension mount, seatbelt anchor) will fail if it has weakened the structure. Cost varies enormously: welding repairs £100 to £500+.
- Sharp edges: Damaged bodywork that creates a sharp edge dangerous to pedestrians will fail. Cost: varies by panel.
9. Registration Plates (2% of all failures)
- Illegible plates: Faded, dirty, or damaged plates that cannot be read clearly will fail. Replacement: £15 to £30 per plate.
- Illegal fonts or spacing: Modified plates with non-standard fonts, misplaced screws affecting characters, or wrong spacing will fail.
10. Seatbelts (2% of all failures)
- Frayed or damaged belts: Any visible damage to the webbing is a fail.
- Buckle not latching: Seatbelt buckles must click securely and hold under load.
- Retractor not working: The belt must retract smoothly and lock under sudden force.
Pre-MOT Checklist: 15-Minute Walk-Around
Before your MOT, spend 15 minutes checking these items. Most can be fixed at home for under £50:
- Walk around the car and check every light: headlights (dip and main beam), indicators (front, rear, side), brake lights, fog lights, reverse lights, number plate lights.
- Check all four tyres for tread depth (1.6mm minimum), damage, bulges, and matching sizes on each axle.
- Check windscreen for chips and cracks, especially in the driver's swept area.
- Test wiper blades for streaking or juddering. Replace if worn.
- Top up washer fluid.
- Check mirrors for damage and secure mounting.
- Test the horn.
- Check number plates are clean, legible, and properly fixed.
- Test all seatbelts for smooth operation and secure latching.
- Check the handbrake holds the car firmly.
- Listen for unusual knocking from the suspension when driving over bumps.
- Look under the car for obvious fluid leaks.
- Ensure the engine management light is not illuminated on the dashboard.
- If you have a diesel, take the car for a 20-minute motorway run before the test to regenerate the DPF.
- Check the fuel filler cap seals properly (it is a testable item).
What to Do If Your Car Fails
If your car fails its MOT, you have several options:
- Free retest: If the car is retested at the same garage within 10 working days, the retest is free (for the failed items only).
- Partial retest: If you leave the car at the testing station and have it repaired there, the retest of failed items is free.
- Driving a failed car: You can only drive a car that has failed its MOT to a pre-booked test or to a garage for repairs. Driving for any other purpose is illegal and can result in a £1,000 fine and 3 penalty points.
Check Your Car's MOT History
Knowing your car's history helps you predict what might fail. Our free car check tool shows every MOT test your car has had, highlights patterns in advisories and failures, and predicts likely future issues based on the car's history and make/model data. Enter the registration number to see the full picture.
You can also check whether a car you are thinking of buying has a clean MOT history or a pattern of expensive failures. This is one of the most valuable checks you can do before handing over money for a used car.