Around 1 in 3 cars fail their MOT in the UK every year — and the majority of failures are for faults you can spot and fix yourself before the test. Here are the most common MOT failure reasons, how much they cost to fix, and what to check before you book your car in.
MOT Failure by the Numbers
~35%
of UK cars fail their MOT first time
£50+
average cost of a retest and minor repair
7 of 10
top failures are easily preventable
The DVSA publishes annual MOT failure data and year after year the same categories top the list — lighting, tyres, brakes and the engine management light. Most of them are things any driver can check at home in under 20 minutes.
Good to know: Since 2018 MOT results are split into three categories — Dangerous (cannot drive away), Major (fail, must fix before driving) and Minor/Advisory (noted but passes). We've flagged the typical category for each failure below.
Top 10 Most Common MOT Failure Reasons
The single most common MOT failure every year. A blown bulb — headlight, brake light, indicator or number plate light — is an instant fail. Takes seconds to check and costs very little to fix before your test.
💷 Bulb: £3–£25
✓ Check yourself in 5 mins
Tread depth below 1.6mm, sidewall damage or bulges are instant fails. Use a 20p coin — if the outer band is visible, replace before your test. Incorrect tyre size or mixing tyre types also causes failures.
💷 Per tyre: £60–£180
✓ Check with a 20p coin
Worn brake pads, corroded discs, uneven braking or a brake fluid leak all cause failures. A brake imbalance test is carried out during the MOT — if one side grabs harder than the other, it fails.
💷 Pads + discs: £120–£300 per axle
✓ Listen for squealing or grinding
Any chip or crack in the driver's critical zone (the 290mm band swept by the wiper in front of the driver) is a fail. Wiper blades that smear, skip or fail to clear the screen properly are also commonly failed.
💷 Wiper blades: £10–£40
✓ Test wiper performance on a wet screen
Since 2018 an illuminated EML is an automatic MOT fail under "driver information systems." Even if your car drives perfectly, it will not pass. The underlying fault must be diagnosed and resolved before your test.
💷 Varies: £80–£600+
✓ Get a diagnostic before your test
Worn shock absorbers, failing ball joints, damaged wishbones or worn anti-roll bar drop links are all commonly failed. A clunking noise over bumps or uneven tyre wear can indicate suspension wear.
💷 Drop links: £60–£150
✓ Listen for clunks over bumps
Petrol cars must pass an emissions test at idle. Diesel cars face a smoke opacity test. A failing catalytic converter, blocked DPF or faulty oxygen sensor commonly causes emissions failures.
💷 Cat replacement: £300–£900
✓ Check for visible smoke or strong exhaust smell
Frayed webbing, a belt that won't retract properly or a buckle that doesn't click securely are instant fails. Check all seatbelts including rear — not just the driver's belt.
💷 Per belt: £80–£200
✓ Test all belts before your MOT
The horn must produce a continuous tone and be audible. A surprisingly common failure — many drivers don't test their horn until the MOT tester asks. Takes two seconds to check before your test.
💷 Replacement: £20–£80
✓ Press and hold — must be continuous
Cracked, faded or incorrectly spaced number plates fail. The number plate light must also work — one of the most overlooked checks. Non-standard fonts on aftermarket plates are an increasingly common failure reason.
💷 New plates: £20–£50
✓ Check plate condition and light
Warning Light On Before
Your MOT? Find Out Now.
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Typical MOT Repair Costs in the UK
| Fault | Typical Fix Cost | DIY Possible? |
|---|
| Blown bulb (headlight/brake) | £5–£30 | Usually yes |
| Wiper blades | £10–£40 | Yes |
| Tyre (per tyre) | £60–£180 | No |
| Brake pads (per axle) | £80–£180 | With experience |
| Brake pads + discs (per axle) | £120–£300 | With experience |
| Anti-roll bar drop links | £60–£150 | With experience |
| Shock absorbers (per pair) | £150–£400 | No |
| Catalytic converter | £300–£900 | No |
| Engine management fault | £80–£600+ | No |
| Seatbelt replacement | £80–£200 | No |
Pre-MOT Checklist — Do This the Week Before
Run through these checks yourself before your MOT. Most take under a minute and could save you a retest fee.
All lights working — headlights, brake lights, indicators, reverse light, number plate light, fog lights
Tyre tread depth — 20p coin test. If the outer band shows, replace before your test
Tyre pressure — inflate to correct PSI shown in door sill or handbook
Windscreen — no chips or cracks in the driver's swept zone
Wiper blades — clean screen without smearing or skipping
Horn — press and hold, must produce a continuous tone
All seatbelts — pull fully, check for fraying, test buckle clicks and releases
Dashboard warning lights — none should stay on after starting. EML on = automatic fail
Number plates — clean, undamaged, correct spacing, plate light working
Fluid levels — oil, coolant, brake fluid, screen wash all topped up
Want the full printable version? Download our free
25-point Car Health Checklist — covers all MOT prep checks plus ongoing maintenance. Free PDF, no sign-up needed.
Engine Management Light On Before Your MOT?
Don't attempt the MOT with the EML on. It is an automatic major fail — you'll pay for the test, a retest and the repair on top. Before spending £60 at a garage just to find out what the fault is, run a MotorLoom diagnostic for £1.99. Describe your symptoms and get likely fault causes, repair costs and a full MOT risk assessment instantly.
Summary
The most common MOT failures in the UK are lighting faults, tyre condition, brakes, windscreen issues and the engine management light — all of which you can check yourself before your test. A simple pre-MOT check takes 20 minutes and could save you £50–£100 in retest fees.
Got a warning light or fault you're not sure about? A MotorLoom diagnostic report gives you the likely cause, repair cost and MOT risk for £1.99 so you can go into your MOT with confidence.
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