The most common reasons cars fail their MOT (and how to avoid them)

Nobody enjoys an MOT fail. It costs time, often money, and sometimes means a car can't be driven until it's fixed. Many of them, though, come down to simple, cheap faults you can find and fix before the test.

Why so many cars fail on simple things

Our analysis of DVSA's 2023 data, covering 32.7 million first MOT attempts, shows the pattern clearly: 11.3% of cars failed on lights and electrics, 8.9% on suspension, 6.8% on brakes and 6.3% on tyres. Many of these faults are things the owner could have spotted in a few minutes: a bulb, a wiper blade, a tyre, an empty washer bottle.

Fixing them yourself, or having them done before the test, means you're not paying for a retest or losing the use of your car. If it does fail, our guide to MOT retest rules explains how to get a free retest.

The usual suspects

Lighting and signalling

This is the area that catches out the most people, because bulbs fail without warning and you can't see your own brake lights. Testers check:

• headlamps (dipped and main beam), including aim
• sidelights, rear lights and brake lights
• indicators and hazard lights
• the rear fog lamp and number plate lamp
• reflectors and the condition of lenses

How to avoid it: once a month, park facing a wall or garage door and switch through every light. Ask someone to press the brake pedal while you look at the back. Replace any blown bulb, and replace both headlamp bulbs together if one goes, as the other is often close behind.

Suspension

Suspension failures are often the most expensive. Testers check for worn ball joints and bushes, broken or corroded springs, leaking shock absorbers and damaged mountings.

How to avoid it: listen for knocking over bumps and clunks when turning. If last year's test noted a worn bush or slight play in a joint, assume it'll fail this year and get it quoted in advance. You can see last year's notes with our MOT advisories check.

Brakes

Brakes are tested for efficiency, balance between the wheels, and the condition of discs, pads, pipes and hoses. The handbrake (or electronic parking brake) is tested too.

How to avoid it: pay attention to warning signs, such as grinding or squealing, a soft pedal, or the car pulling to one side. If the handbrake needs pulling up further than usual, it may need adjusting.

Tyres and wheels

Testers check tread depth (the legal minimum for cars is 1.6mm across the central three-quarters of the tread), cuts, bulges, exposed cords, tyre size and type, and that wheel nuts are secure.

How to avoid it: use a tread depth gauge or the edge of a 20p coin as a rough guide. Look along the sidewalls for bulges and cuts. Check that the spare isn't needed in place of a damaged tyre. Tyres aren't just an MOT issue either: driving on illegal tyres can mean up to £2,500 and 3 points per tyre.

For the full rules, see our guide to tyre tread depth and the MOT.

Visibility: windscreen, wipers and washers

The windscreen is divided into zones. Damage in the area directly in front of the driver is treated more strictly than damage elsewhere. Wipers must clear the screen effectively, and the washers must work.

How to avoid it: get chips repaired early, as a small chip is cheap to fix but can spread into a crack. Replace wiper blades if they smear or judder. Fill the washer bottle before the test, as an empty bottle is one of the easiest failures to avoid.

Dashboard warning lights

Warning lights for systems such as ABS, airbags, electronic stability control, power steering and engine management can cause a fail.

Our guide to dashboard warning lights and the MOT lists which lights fail and when.

How to avoid it: don't ignore a warning light hoping it'll go away. A garage with diagnostic equipment can read the fault code. Sometimes the cause is minor, such as a sensor, but it still needs fixing before the test.

Exhaust and emissions

The tester checks that the exhaust is secure and doesn't leak, and measures emissions. Petrol cars are tested for carbon monoxide and hydrocarbons. Diesels are tested for smoke. Diesel cars fitted with a particulate filter (DPF) can fail if the filter has been removed or tampered with.

How to avoid it: take the car for a decent run before the test, so the engine and exhaust are fully warmed up. Fix exhaust blows promptly, as a small leak can affect the reading.

Number plates

Plates must be secure, legible, made from reflective material and display the registration in the correct font and spacing. Personalised spacing, stylised fonts and badges in the wrong place can fail, and they can also lead to a fine of up to £1,000 outside the test.

How to avoid it: give your plates a wipe, check they're not cracked, and replace non-standard plates with legal ones from a registered supplier.

Other things that catch people out

• Seatbelts that don't retract or latch properly
• The horn not working
• Mirrors that are cracked or missing
• Doors that don't open from inside or outside
• Fuel cap missing or not sealing
• Excessive clutter that stops the tester inspecting the seatbelts or boot floor

What fails at different ages

The likely problems change as a car gets older, so it helps to know what to look for at each stage.

• First MOT (around three years old). Tyres, wiper blades and bulbs are the usual culprits. Cars that do high mileage in their first three years can also need brake pads and discs.
• Five to ten years old. Suspension bushes, ball joints and springs start to wear. Brake discs and pads are often due again. Exhaust components, particularly on cars that do lots of short trips, begin to corrode.
• Over ten years old. Corrosion becomes more significant, especially on brake pipes, subframes and sills. Rubber parts such as hoses, gaiters and bushes perish with age, even on low-mileage cars.

Knowing this, you can focus your checks and budget. A ten-year-old car with no suspension work in its history is more likely than not to need some soon. Vans follow a similar pattern but faster, because of the loads and mileage they do; see our van MOT check.

Your plan for passing first time

1. Look up last year's advisories and deal with any that have got worse.
2. Work through our pre-MOT checklist a week before the test.
3. Fix the cheap items (bulbs, wipers, washer fluid) yourself.
4. Get warning lights diagnosed.
5. Book within the early-testing window, so a fail doesn't take the car off the road. Our MOT due date checker shows when it opens.
6. Know the maximum fee before you book. For a car it's £54.85, and our MOT cost calculator covers other vehicles.

None of this guarantees a pass, but it removes the most common and most avoidable reasons for failing.