MOT Failure Statistics: The Full Picture
Every year, the Driver and Vehicle Standards Agency (DVSA) publishes data on the most common reasons vehicles fail their MOT test. Understanding these statistics helps you focus your pre-MOT checks on the areas most likely to cause problems. Below are the top failure categories ranked by frequency, based on analysis of millions of MOT tests conducted across England, Scotland, and Wales. You can also see failure rates broken down by make and model for a more specific view.
| Failure Category | Share of Failures | Typical Fix Cost |
|---|---|---|
| Lights & Signalling | ~30% | 3 - 50 |
| Suspension | ~25% | 100 - 400 |
| Brakes | ~18% | 100 - 300 |
| Tyres | ~10% | 50 - 80/tyre |
| Visibility (wipers, screen) | ~8% | 10 - 150 |
| Exhaust & Emissions | ~4% | 50 - 500 |
| Steering | ~3% | 80 - 350 |
| Body & Structure | ~2% | 100 - 1,000+ |
1. Lights & Signalling (~30% of Failures)
Lighting defects are the number one cause of MOT failure and account for roughly three out of every ten failures. The most common issues include blown bulbs, headlights that have gone out of alignment, cracked or moisture-filled lens covers, and indicators that flash at the wrong rate.
What Is Checked
- Headlights (dipped and main beam) for operation, aim, and colour
- Front and rear position lights (sidelights)
- Stop lights (brake lights), including high-level brake light
- Direction indicators and hazard warning lights
- Rear fog light(s)
- Number plate light
- Rear reflectors
- Headlight aim — tested with a beam setter machine
How to Avoid This Failure
- Walk around the car with the ignition on and check every bulb. Ask someone to press the brake pedal while you check the rear.
- Replace blown bulbs immediately — most are under 10 pounds and can be fitted in minutes with the owner's manual.
- If a headlight lens is cloudy or yellowed, use a restoration kit (around 15 pounds) to clear it before the test.
- If you have replaced headlight bulbs with aftermarket LEDs, check they produce a correct beam pattern — badly aimed LEDs are a common reason for referral.
2. Suspension (~25% of Failures)
Suspension faults are the second most common failure category. The MOT tester checks shock absorbers, springs, wishbone bushes, anti-roll bar links, ball joints, and wheel bearings. Many of these components wear gradually, so a deterioration from advisory to failure can happen between annual tests.
What Is Checked
- Shock absorbers — leaking fluid or excessive travel
- Coil springs — cracked, broken, or corroded
- Wishbone and suspension arm bushes — worn, split, or perished
- Anti-roll bar links and bushes
- Ball joints — excessive play or damaged boots
- Wheel bearings — roughness or excessive play
- Mounting points — corroded or weakened by rust
How to Avoid This Failure
- Bounce each corner of the car firmly and release. If it bounces more than once, the shock absorber is likely worn.
- Listen for knocking or clunking sounds when driving over bumps or turning at low speed — this indicates worn bushes, drop links, or ball joints.
- Inspect coil springs visually for cracks. Broken springs are most common in winter due to salt corrosion.
- If your vehicle has had suspension advisories on previous MOTs, have the items inspected before the next test.
3. Brakes (~18% of Failures)
Braking defects account for nearly one in five MOT failures. Testers use a roller brake tester (or decelerometer for vehicles over 3,000 kg) to measure braking efficiency and check for imbalance between the left and right sides. The minimum service brake efficiency is 58% and the minimum parking brake efficiency is 16%.
What Is Checked
- Service brake efficiency (minimum 58%)
- Parking brake efficiency (minimum 16%)
- Brake imbalance — a difference of more than 30% between left and right sides results in a failure
- Disc and drum condition — excessive wear, scoring, or cracks
- Brake pad and shoe thickness
- Brake hoses and pipes — leaks, corrosion, chafing, or bulging
- Brake fluid reservoir level
- ABS warning light — must illuminate at ignition and extinguish within a few seconds
How to Avoid This Failure
- Check brake pads through the wheel spokes — if the friction material is less than 3mm thick, replace them before the test.
- Before arriving at the test centre, drive and brake firmly several times to ensure the brakes are warm and the discs are free of surface rust.
- Ensure the handbrake holds the car on a gentle slope. If you need to pull it excessively high, the cable likely needs adjusting.
- If the ABS warning light is on, have the system diagnosed before the MOT — a permanently illuminated ABS light is an automatic major failure.
4. Tyres (~10% of Failures)
Tyre defects are the fourth most common cause of MOT failure. The legal minimum tread depth in the UK is 1.6mm across the central three-quarters of the tread width, around the entire circumference. However, most motoring organisations recommend replacing tyres at 3mm, as stopping distances increase significantly below this level.
What Is Checked
- Tread depth — minimum 1.6mm across the central three-quarters
- Tyre condition — cuts, bulges, cords exposed, or cracking
- Tyre size and type — must match the vehicle manufacturer specification
- Tyre compatibility — the same type (radial or cross-ply) must be fitted on each axle
- Tyre pressure — grossly under-inflated tyres may be failed
How to Avoid This Failure
- Use a 20p coin to check tread depth. Insert it into the main grooves — if the outer band of the coin is visible, the tyre is close to or below the 1.6mm limit.
- Inspect tyre sidewalls for bulges, cuts, or cracking. Sidewall damage is a common failure that drivers often overlook.
- Check tyre pressures and inflate to the manufacturer's recommended levels (usually found on a sticker inside the driver's door frame).
- Ensure all four tyres are the correct size and speed rating for the vehicle. Mixing radial and cross-ply tyres on the same axle is a failure.
5. Visibility (~8% of Failures)
Visibility defects cover the windscreen, wiper blades, washers, and mirrors. A chip or crack in the windscreen can result in a failure depending on its size and position. The MOT defines two zones: Zone A (a 290mm-wide band centred on the steering wheel) where damage greater than 10mm is a failure, and the swept area outside Zone A where damage greater than 40mm is a failure.
What Is Checked
- Windscreen condition — chips, cracks, and surface damage in the swept area
- Wiper blades — splits, tears, or missing rubber
- Wiper operation — must clear the screen effectively
- Windscreen washer operation — jets must provide adequate fluid to the screen
- Interior and exterior mirrors — condition and security
How to Avoid This Failure
- Replace wiper blades if they leave streaks or have visible splits in the rubber. A pair costs around 10 to 25 pounds.
- Fill up the washer fluid reservoir before the test. Empty washers are an instant failure.
- Inspect the windscreen for chips. Small chips outside Zone A can often be repaired for free through your car insurance.
- Ensure both wing mirrors and the interior mirror are securely attached and the glass is intact.
6. Exhaust & Emissions (~4% of Failures)
Exhaust and emissions failures cover both the physical condition of the exhaust system and the vehicle's tailpipe emissions. For petrol vehicles first used from 1 August 1975, CO emissions are tested. For diesel vehicles first used from 1 August 1979, smoke opacity is tested. Since February 2014, diesel MOT emission limits have been significantly tightened.
What Is Checked
- Exhaust system security, condition, and leaks
- Catalytic converter presence and condition
- Diesel Particulate Filter (DPF) presence — removal is an automatic failure
- Tailpipe emissions — CO, HC, and lambda (petrol); smoke opacity (diesel)
- Engine management light (EML) — must not be illuminated during emissions test
How to Avoid This Failure
- Take the car for a 20-minute drive before the test so the catalytic converter and DPF reach operating temperature. This is especially important for diesels with DPFs.
- If the engine management light is on, have the fault diagnosed and cleared before the MOT. A lit EML is a major failure regardless of the underlying cause.
- Check for blowing exhaust joints — listen for a rasping sound under acceleration, which suggests a leak.
- Use the correct grade of engine oil. Overly thick or degraded oil can increase emissions.
7. Steering (~3% of Failures)
Steering defects include excessive play in the steering system, worn track rod ends, damaged gaiters, power steering fluid leaks, and power steering warning lights. The tester will rock the steering wheel and observe the front wheels for excessive free play.
What Is Checked
- Steering wheel free play and column security
- Steering rack gaiters — splits, tears, or missing
- Track rod ends and ball joints — wear and security
- Power steering — fluid level, leaks, and operation
- Power steering / EPAS warning light
How to Avoid This Failure
- With the engine running, turn the steering wheel slightly left and right. If you feel excessive movement before the front wheels respond, there may be wear in the track rod ends or steering rack.
- Check the power steering fluid level (if hydraulic). Top up if low and inspect for leaks around the rack and pump.
- Listen for knocking sounds when turning the wheel — this can indicate worn inner or outer track rod ends.
8. Body & Structure (~2% of Failures)
Structural corrosion is one of the more expensive MOT failures to rectify. The tester inspects load-bearing areas of the body shell — sills, floor pans, chassis legs, subframe mounting points, and spring mounting areas — for excessive corrosion or damage that compromises structural integrity. This category also covers doors, bonnet catches, bumpers, and sharp edges.
What Is Checked
- Structural integrity of sills, floor pans, and chassis rails
- Subframe and suspension mounting points
- Door security — hinges, catches, and operation
- Bonnet catch security
- Bumper security and sharp edges
- Fuel tank and filler cap security
- Towbar condition and security (if fitted)
How to Avoid This Failure
- Inspect the sills, wheel arches, and underside of the car for rust. Pay close attention to the jacking points and spring mounting areas.
- If corrosion is found, have it repaired by a welder before the MOT. Surface rust alone is not a failure, but corrosion that has weakened the metal is.
- Check that all doors open and close securely, the bonnet catch holds firmly, and there are no sharp edges from accident damage or missing trim.
Check Your Vehicle's MOT History
See past failures, advisories, and mileage readings for any UK vehicle. Use the MOT history to identify recurring problems and plan repairs before your next test.
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