The 10 most common MOT failures (and how to avoid them)
Around a third of cars fail the MOT first time — and most fail on small, avoidable things. Here are the ten faults that catch people out, how to spot each one at home, and a ten-minute pre-test check.
The 10 things that fail MOTs most often
- Lights & signals — the number-one failure, and usually just a blown bulb. Walk round the car with sidelights, headlights, indicators, brake lights and fog lights on.
- Tyres — below the 1.6mm legal tread limit, uneven wear, or damage. Use the 20p test at several points across each tyre.
- Brakes — worn pads or discs, or imbalance between wheels. Listen for grinding or squealing and feel for any pull under braking.
- Suspension — worn bushes, joints or springs. Knocking over bumps or the car sitting unevenly are warning signs.
- Driver's view of the road — smeary wipers, empty washer bottle, or anything obstructing the swept area of the windscreen (including large chips) can all fail.
- Number plates — dirty, faded, cracked or incorrectly spaced plates are an easy fail. Give them a wipe.
- Registration lights & reflectors — small rear bulbs and cracked reflectors get missed because you rarely see them yourself.
- Seatbelts — check each one clicks in firmly, retracts, and isn't frayed or damaged.
- Windscreen wipers & washers — split or worn blades that smear, or washers that don't reach the screen.
- Dashboard warning lights — an engine management, airbag or ABS light staying on is an automatic fail. Get it diagnosed first.
Your 10-minute pre-MOT check
None of this needs tools or know-how — it's the quick walk-round we wish every customer did the week before their test:
- Turn on every light and walk around the car — get someone to press the brake pedal so you can see the brake lights.
- Do the 20p tread test on all four tyres and check they look properly inflated.
- Top up the screen washer bottle and test the wipers clear the glass without smearing.
- Press the horn — it needs to work.
- Clean the number plates front and rear so they're clearly legible.
- Click each seatbelt in and give it a firm tug.
- Start the car and check no warning lights stay on once it's running.
Anything you're not sure about, we can check and fix before the test — on your driveway, so a borderline car doesn't have to risk the drive to a garage.
Common questions
What is the most common reason cars fail the MOT?
Lighting and signalling faults are consistently the single most common MOT failure — usually just a blown bulb. They're also the cheapest to prevent: a two-minute walk around the car with the lights on catches most of them.
How many cars fail their MOT first time?
Around a third of cars fail their MOT at the first attempt. The striking part is how many of those failures are for small, avoidable things — bulbs, tyres, wipers and washer fluid — rather than serious mechanical faults.
What is the 20p tyre test?
Pop a 20p coin into your tyre's main grooves. The outer band of a 20p is roughly 1.6mm — the legal minimum tread depth. If you can see the band when the coin is in the groove, your tread may be too low and the tyre needs checking. Do this at a few points across each tyre.
Can I check my car myself before the MOT?
Yes, and it's well worth ten minutes. Check every bulb works, tyres have tread and are inflated, washer fluid is topped up, wipers clear the screen without smearing, the horn works, number plates are clean and legible, and no warning lights stay on. That covers the majority of common failures.
Does a warning light on the dashboard cause an MOT failure?
It can. A illuminated engine management light (MIL), airbag warning light, or several other warning lights are an automatic failure. If one is showing, get it diagnosed before the test rather than paying for a failure.
Can you fix these things at my home before the test?
Yes — as mobile mechanics we can carry out a pre-MOT check and sort bulbs, wipers, tyres, brakes and more on your driveway anywhere in Gloucestershire, so your car passes first time instead of failing on something small.
Want to pass first time?
We'll carry out a pre-MOT check and fix bulbs, tyres, wipers and brakes at your home or workplace across Gloucestershire — open 24/7, no callout fee within 5 miles.
More advice: MOT advisories explained · Can you drive with an expired MOT? · Free MOT check