MOT common failures: the 10 most common reasons cars fail the MOT
Around one in three UK cars fails its first MOT. The majority of failures are for items that can be checked and fixed cheaply before test day. This guide covers the ten most common failure categories, how to check them yourself, and typical repair costs if you need a garage.
DVSA data: Lighting faults alone account for roughly 30% of all first-time MOT failures — more than tyres and brakes combined. Most bulb failures can be fixed in under ten minutes for under £10.
Lighting and signalling
~30% of all failuresFaulty lights are the single most common MOT failure. Any failed bulb — headlight, brake light, indicator, fog light, number plate light — is an immediate fail. Light failure is also the easiest thing to check and fix yourself in under ten minutes.
How to check it yourself:
Walk around the car with someone pressing each light control: headlights (dipped and full beam), both indicators, hazard lights, brake lights, reversing lights, and fog lights. Check number plate lights too. Replace any blown bulbs before your test — they cost £2 to £10 at any motor factor.
Typical repair cost: £5 to £60 depending on the bulb and whether the housing is accessible
Tyres
~10% of all failuresTyres are checked for tread depth (minimum 1.6 mm across the central three-quarters of the tyre), condition (no cuts, bulges, or exposed cord), and correct fitment. A single illegal tyre is an immediate fail — and a £2,500 fine if caught on the road.
How to check it yourself:
Use a 20p coin as a rough guide: if the outer rim of the coin is visible when inserted into the tread, the tyre is at or near the legal limit. Check all four tyres and the spare. Look for sidewall bulges, cuts, or uneven wear (which may indicate a wheel alignment issue).
Typical repair cost: £60 to £150 per tyre fitted, depending on size and brand
Brakes
~10% of all failuresBrakes are checked for performance (the car must stop straight and within a minimum deceleration rate), condition (pad thickness, disc condition, handbrake operation), and fluid level. Uneven braking — pulling to one side — is a common cause of failure.
How to check it yourself:
In a safe, empty area, test emergency braking at 20 mph. The car should stop without pulling to either side. Listen for grinding or squealing. Check the handbrake holds on a slope. Low brake fluid can indicate worn pads or a leak — both fail.
Typical repair cost: £80 to £200 for front pads; £150 to £350 for pads and discs
Driver's view of the road
~8% of all failuresThis category covers windscreen damage and wipers. A chip or crack in the driver's swept zone (the area cleared by the wipers) larger than 10 mm is an immediate fail. Chips outside that zone up to 40 mm are also a fail. Failed wiper blades that smear or chatter are a fail too.
How to check it yourself:
Check the windscreen in daylight for chips or cracks. Run the wipers on a wet screen — they should clear cleanly without smearing. Replace wiper blades if they streak; blades cost £10 to £30.
Typical repair cost: Windscreen chip repair: £30 to £50; full replacement £150 to £400. Wiper blades: £10 to £30.
Fuel and exhaust systems
~7% of all failuresEmissions are tested (especially on older petrol cars and diesels). A car must not emit excessive CO, hydrocarbons, or visible smoke. Exhaust leaks upstream of the catalytic converter also fail. A loose or blowing exhaust joint is a straightforward fail.
How to check it yourself:
Listen for blowing or rattling from the exhaust, especially when cold. Excessive black, blue, or white smoke from the exhaust is a sign of emissions failure. For diesel cars, a blocked DPF (diesel particulate filter) commonly causes high emissions — a long motorway run can help clear it.
Typical repair cost: Exhaust repair: £50 to £300. Catalytic converter: £150 to £600. DPF clean or replacement: £100 to £1,000+.
Steering and suspension
~6% of all failuresWorn ball joints, track rod ends, shock absorbers, and anti-roll bar bushes are checked. A car that knocks on bumps or pulls to one side during braking is likely to fail. Steering play (excessive movement before the wheels respond) also fails.
How to check it yourself:
On a quiet road, let go of the wheel briefly at 30 mph — the car should track straight. Knocking over speed bumps or rough ground suggests worn suspension. Power steering fluid that is low or milky indicates a leak.
Typical repair cost: Track rod ends: £80 to £200. Shock absorbers: £150 to £400 per axle. Ball joints: £100 to £250.
Body and structure
~5% of all failuresThe tester checks for sharp edges on bodywork that could injure a pedestrian, and for significant corrosion in structural areas such as the sill, floor pan, or subframe. Minor cosmetic rust does not fail, but rust that penetrates structural metal or that is within 30 cm of a seat belt mounting point does.
How to check it yourself:
Inspect under the car with a torch, particularly the sill edges, floor pan, and the area around seat belt mounting points and subframe mounts. Press on any suspected rust — if it is soft or flaky, it may be structural.
Typical repair cost: Varies enormously: £100 to £2,000+ depending on the extent of the rust and whether welding is required.
Mirrors
~3% of all failuresYour car needs at least two functional mirrors that are not cracked or obscured. The driver's door mirror and the interior rear-view mirror must be intact and adjustable. A missing or badly cracked passenger door mirror is also a fail.
How to check it yourself:
Check all mirrors are intact and give a clear, undistorted view. Cracks across the reflective surface fail; stone chips to the glass edge do not.
Typical repair cost: Mirror glass: £15 to £80. Mirror housing or motor replacement: £50 to £250.
Registration plates
~2% of all failuresNumber plates must be legible, properly fixed, correctly lit, and conform to the standard format: white at the front, yellow at the rear, black lettering on a reflective background. Plates that are cracked, faded, or have non-standard spacing or fonts are an immediate fail.
How to check it yourself:
Check both plates are clean, firmly attached, and fully legible. Non-standard fonts (e.g. 3D printed characters with italic spacing) are illegal and will fail. Confirm the rear plate light works.
Typical repair cost: Replacement plates: £15 to £30 per pair from a registered supplier.
Seatbelts
~2% of all failuresAll seatbelts present in the vehicle must retract, latch, and lock correctly. A belt that does not retract, that has fraying or cuts in the webbing, or that fails to lock in a sharp-stop test, is an immediate fail.
How to check it yourself:
Test each belt: pull the tongue out fully and allow it to retract. Check the webbing for fraying or cuts. Pull sharply while buckled in — the belt should lock. Check the buckle latches and releases cleanly.
Typical repair cost: Seatbelt repair or replacement: £80 to £200 per belt.
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Frequently asked questions
What are the most common reasons for an MOT failure?
The most common MOT failure categories are lighting and signalling (about 30% of all failures), tyres (10%), brakes (10%), driver's view of the road such as windscreen chips and wiper condition (8%), and fuel and exhaust emissions (7%). In most years, simple lighting faults — a blown brake light or indicator bulb — account for more MOT failures than any other single cause.
What percentage of cars fail their MOT?
DVSA statistics consistently show that around 30 to 35% of all cars fail their MOT first time. Of those failures, a significant proportion are for minor items (lights, wiper blades, number plates) that could have been checked and fixed before the test at a fraction of the retest cost. Older cars and those that cover fewer miles per year tend to fail at higher rates.
What is a dangerous fail at an MOT?
From May 2018, MOT failures are classified into three categories. A Dangerous defect is one that poses an immediate risk to road safety — the car must not be driven until it is repaired. A Major defect must be fixed and the car retested. A Minor defect (previously an advisory) is recorded but does not cause a fail; it should be monitored and repaired soon. Dangerous items include severely corroded brake pipes, tyres with exposed cord, and non-functional steering.
Can I drive my car home if it fails its MOT?
If the car has a Dangerous fail, you cannot legally drive it on public roads. If the fail is for Major defects only, you can drive it home or to a garage for repairs, but you are taking on legal risk if the defect contributed to an incident. If your MOT expired before the test, you cannot legally drive the car regardless of the outcome. Check your certificate carefully before driving away.
What does a free MOT retest include?
If your car fails and you have the repairs done at the same garage within 10 working days, most garages offer a free or reduced-price retest of the failed items only. If you take the car elsewhere for the retest, the garage must conduct a full MOT and charge accordingly. Always confirm the retest policy with your garage before booking repairs elsewhere.
Does a windscreen chip fail an MOT?
Yes, in certain positions. A chip or crack in Zone A (the area directly in front of the driver, approximately 290 mm wide) larger than 10 mm is an immediate fail. In the remaining swept area (Zone B, the area the wipers clear), damage larger than 40 mm fails. Outside the swept area, damage larger than 40 mm can also fail if it obscures the driver's view. A chip repair carried out by a professional typically restores the structural integrity and removes the visual distortion that causes the fail.
Can I get an MOT if my car has warning lights on?
Warning lights are part of the MOT check. An engine management light (EML) on during the test is typically a Major fail. A dashboard warning light that should not be illuminated — such as an ABS warning, airbag warning, or brake warning — also fails. Turn warning lights off before your test by having the fault diagnosed and repaired.
How long does an MOT take?
A standard car MOT takes between 45 minutes and one hour if the car passes. If additional checks are needed or if the tester finds items to investigate further, it may take longer. It is best to allow 90 minutes and not plan anything time-critical immediately after dropping the car off.
How can I reduce the chance of my car failing its MOT?
The most effective preparation is a 15-minute pre-MOT check you can do yourself: test all lights (headlights, brake lights, indicators, fog lights, number plate lights), check tyre tread depth and condition, confirm wipers clear cleanly, ensure the windscreen has no qualifying chips, check the horn works, and check all fluid levels. This catches the most common cheap-to-fix fails before you pay for a test.