Your car can fail its MOT on dozens of grounds, from a blown bulb to structural rust and most owners are caught off guard by a failed mot because they didn't know what testers look for. The 15 most common failure points affecting driver and vehicle safety appear across every major vehicle system, with the checks you can do at home before your test date.
What the MOT test actually checks
The MOT test checks your car against DVSA safety and emissions standards every year once it turns 3 years old (4 years in Northern Ireland). Testers work through every safety-critical system, checking that lights are working, tyres are sound, brakes respond well, steering is accurate, suspension is smooth, windscreen is clear, exhaust meets standards, and bodywork is intact.
Your car's registration date and plates matter for a handful of checks: vehicles first used on or after 1 March 2018 must have a rear fog light fitted, and exhaust noise limits are stricter for cars registered after that date. Around 7.3 million vehicles fail their initial MOT each year in Great Britain, roughly 1 in 3, with 8% carrying at least 1 dangerous defect. Check your own car against the most common failure points below before the test.
MOT failure categories: major, dangerous, and minor
Not every MOT defect is equal. Since May 2018, the DVSA has sorted all faults into 4 outcome categories and only 2 of them mean your car has officially failed.
| MOT Outcome | Test Result | Driving Implications |
|---|---|---|
| Dangerous defect | Fail | Must NOT be driven — illegal even to a repair garage without a pre-booked appointment |
| Major defect | Fail | Cannot drive legally until repaired and a retest passed |
| Minor defect | Pass | Recorded on your certificate; monitor the component |
| Advisory | Pass | Early warning; inspect before your next test |
Around 8% of all UK MOT tests, roughly 2.4 million vehicles a year, produce at least 1 dangerous defect. Driving without a valid MOT carries a fine of up to £1,000.
Which car systems are common MOT failures?
Two datasets cover this, and they don't agree.
DVSA records across 559 million tests rank suspension top at 18.8%, followed by tyres at 18.5%, brakes at 17.8%, lights at 13.3%, and emissions/noise/leaks at 7.2%. A separate RAC/DVSA analysis weights lighting highest at 25.5%, suspension at 19.4%, brakes at 17%, and tyres at 12%.
Both datasets agree on the order of concern. Across individual items, handbrake inefficiency is the single most-recorded failure — 9.1 million instances in DVSA records.
Driving without a valid MOT carries a fine of up to £1,000. If your car fails its new test after the previous certificate has expired, you cannot legally drive it away unless heading directly to a pre-booked repair.
Lights and indicators in electrical systems
Lamps, reflectors and electrical equipment is the single most common MOT failure category, accounting for approximately 25% of all car MOT fails, roughly 1 in 4 failures traces back to a lighting or signalling fault. DVSA data puts the figure at approximately 25.5% across analysis periods.
Most lighting faults cost a few pounds and 5 minutes to fix. Check every circuit before your test.
Headlight alignment and beam condition
Headlights must illuminate the road ahead without dazzling oncoming drivers. A misaligned beam angled too high is a failure because it blinds other road users. So is a fogged or yellowed lens, which scatters light instead of projecting it cleanly.
Check yours in daylight: do the lenses look cloudy or discoloured? Switch them on at dusk and stand 10 metres ahead, does the beam feel weak or scattered? If so, a garage can realign or polish the lenses before your test.
One point worth knowing for drivers heading to Europe: UK headlights project the beam slightly left to avoid dazzling oncoming traffic on the left-hand side of the road. On the Continent, that same beam dazzles drivers coming the other way. Headlight deflector stickers redirect the beam pattern for right-hand driving, they are not an MOT requirement for UK roads, but testers do check that your beam pattern is correctly set for UK use.
Brake lights and rear lights
Brake lights illuminate when you press the pedal; rear lights come on with the headlights. A blown bulb in either circuit is a straightforward failure you can catch yourself in 60 seconds.
Ask someone to stand behind the car while you press the brake, engage reverse, and switch on the headlights. Any light that fails to illuminate is a failure point.
Indicators and hazard lights
Lights and indicators must flash at the correct rate: too slow or too fast signals a bulb fault or a failing relay. Walk around your car with each indicator running, then repeat with the hazard lights. Every corner should flash brightly and evenly.
Number plate illumination
The number plate lamp is the 4th most common individual MOT failure item, responsible for 5.66% of all failure items and it takes seconds to spot. Switch on your headlights after dark and check whether your rear plate is clearly readable. A blown or missing bulb here is a failure, but one of the cheapest fixes on the list.
Tyres and wheels
Tyre faults account for 12% of all MOT failures — up from 10% in 2018–19, and nearly 60% of all dangerous defect classifications are tyre-related. That upward trend matters: tyres are getting worse, not better.
Tread depth below 1.6 mm
UK law requires a minimum tread depth of 1.6 mm across the central three-quarters of the tyre width, measured around the full circumference. The central three-quarters means the middle 75% of the tyre from side to side, the shoulders can wear unevenly without triggering this rule, but the centre band cannot. Testers use a calibrated depth gauge or check the moulded wear indicators built into the tread grooves. Fall below 1.6 mm anywhere in that zone and the tester records a dangerous defect, automatic failure, no exceptions.
Sidewall damage, bulges, and cuts
The sidewalls of your tyres must be intact. Any cut, bulge, or visible deterioration is an automatic failure because it signals the tyre could blow out without warning. A bulge looks like an outward swelling in the rubber, caused by internal cord damage from a kerb strike or pothole. Kneel beside each wheel and run your eyes and fingers along the full sidewall. Cracks, cuts, or any raised lump means the tyre will fail.
Mismatched tyre types on the same axle
Mixing radial and cross-ply tyres on the same axle is illegal in the UK and causes unpredictable handling under braking. Your front pair must match each other, and your rear pair must match each other. Check the sidewall of each tyre: it will state "Radial" or show an "R" in the size code.
Checking tread depth with the 20p test
A 20p coin gives you a fast tread check before your MOT test:
- Find the raised outer border on the edge of the coin.
- Insert the coin into a tread groove at the centre of the tyre.
- If the border is visible above the tread, depth is below 1.6 mm — a failure.
- Repeat at the left, centre, and right of the tread band on each tyre.
- Check all 4 tyres. Any single tyre below the legal limit fails the whole vehicle.
Nearside front tyre tread depth failures are the single most common individual MOT failure item, with 7.2 million recorded incidents, offside front follows at 6.5 million, nearside rear at 4 million. Check the fronts first, since they wear more quickly, but don't skip the rears. Find one below the limit? Replace it before you book, a single tyre failure means the whole car fails, and you'll pay the re-test fee on top of the replacement cost.
Brakes
Brake faults cause approximately 17% of all UK MOT failures and brakes and tyres combined account for 88% of all 'dangerous' defect classifications, the category where your car cannot legally be driven until repaired.
Brake pad and disc wear
Brake pads and discs wear gradually, and the MOT tester checks both visually and with gauges. Pads worn below minimum thickness fail outright. Most cars have a small inspection window in the wheel where you can see the pad material. If it looks thinner than 2–3mm, book a garage check before your test. Discs should be smooth and metallic; deep scoring, cracking, or heavy corrosion are all failure triggers. If your discs show any of those signs, book a brake check before the test, a garage can measure disc thickness and surface condition in under 20 minutes.
Braking imbalance between wheels
All 4 wheels should slow evenly when you brake. The MOT roller brake tester measures each wheel's stopping force independently, a significant imbalance between sides means the car won't stop in a straight line, and that's an automatic failure. You can spot this yourself: if your car pulls left or right under braking on a straight, wind-free road, that's brake imbalance. Book a brake specialist before the test.
Parking brake effectiveness
The handbrake must hold the car securely on a slope. Across 209 million DVSA records from 2005 to 2025, parking brake inefficiency is the single most frequently recorded MOT failure item, with 9.1 million failures logged. Test it yourself: find a safe hill, select Neutral, release the footbrake, and apply the handbrake fully. If the car rolls, it will fail. Excessive lever travel, pulling the handle nearly to its stop before it holds, is also a failure trigger.
Steering and suspension
Suspension faults account for 19.4% of all MOT failures, this is the second most common category after lighting. Testers work through the steering rack, joints, dampers, and bearings methodically, and any component showing excessive play, visible damage, or abnormal movement triggers a major or dangerous defect.
Excessive steering play and column wear
Your steering wheel should respond almost immediately when you turn it. If the wheel moves several degrees before the road wheels react, the tester will flag excessive play, a sign of wear in the steering rack or column. Check it yourself: sit in a parked car and turn the wheel slowly from side to side. If you feel a loose, spongy zone where nothing happens before the wheels begin to move, book a steering inspection before your MOT.
Worn ball joints, track-rod ends, and bushes
Ball joints and track-rod ends link the steering system to the wheels. Worn or perished joints compromise directional control and fail the test. The tester rocks each wheel on the lift and checks for movement in the joints. You can spot early warning signs yourself: listen for clicking or clunking when you turn at low speed, or notice whether the car pulls to one side. Any clunking from the front suspension warrants a professional check.
Shock absorber and spring condition
Leaking dampers or broken springs fail the MOT on sight. Do the bounce test before your appointment: press down firmly on each corner of the car, release, and count the bounces. The car should settle after 1 bounce. More than that, or a wallowing, unsettled feel, points to a worn shock absorber. Also crouch down and look for oil streaks on the damper body, a leaking shock is an automatic failure.
Wheel bearing condition
Wheel bearings let your wheels spin smoothly. Worn bearings produce a rumbling or grinding noise that changes pitch as you steer. Drive at moderate speed and listen: if the noise shifts when you turn left or right, a bearing is likely failing. Testers lift each wheel and rock it, any play or grinding confirms the fault.
Windscreen, wipers, and washers
Windscreen and wiper faults account for 8.7% of MOT failures and the thresholds that separate an advisory from an automatic fail are more precise than most drivers expect.
Windscreen chips and cracks in the driver's zone
Your windscreen is divided into zones, and the rules differ by location. The critical area is a roughly 290mm band centred on the steering wheel, your direct line of sight to the road. Any chip or crack larger than 10mm in that zone is an automatic fail. Outside that zone but still within the wiper-swept area, the limit rises to 40mm. Smaller chips elsewhere are typically advisories.
To check: stand outside and look at the windscreen in good light. Any damage near the steering wheel wider than a 10p coin needs attention before the test.
Wiper blade condition and smear
Wiper blades must clear the windscreen cleanly in a single pass. Split, hardened, or missing rubber strips that leave streaks or chatter across the glass are a failure. Wiper blade ineffectiveness has contributed to a combined 5.5 million MOT failures across DVSA records — nearside and offside blades together, making this one of the most preventable failure causes on the list.
To check: spray your washers and watch both blades sweep. Any streaking, smearing, or juddering means the blades need replacing.
Washer jet function
Washer jets must spray fluid onto the windscreen on demand. Blocked or misdirected jets, cracked hoses, and empty reservoirs have caused 2.9 million MOT failures in DVSA records. The tester activates the system and checks that fluid reaches the glass.
To check: top up the reservoir and activate the washers. If nothing sprays, the jets may be blocked,a thin pin can clear most nozzles in seconds actually.
Engine, exhaust, and emissions
Emissions, exhaust faults, and fluid leaks account for around 5% of MOT failures, a smaller share than brakes or tyres, but the defects here carry some of the harshest severity ratings.
Exhaust emissions above legal limits
Your exhaust emissions must stay within DVSA thresholds set for your vehicle's age and fuel type. The tester measures carbon monoxide (CO), hydrocarbons (HC), and lambda using a specialist tailpipe analyser — you can't replicate this at home. Petrol and diesel engines have different limits, and readings that breach them are a major failure. Exhaust emissions failures account for 3.2 million individual fail items in DVSA records. Visible black smoke from a diesel is the clearest warning sign; a rough-running petrol engine is another. If either applies, book a service first.
Engine warning light illuminated
A lit malfunction indicator lamp (MIL) — the engine warning light on your dashboard, is an automatic major failure at the time of the MOT, regardless of the underlying fault. Check before the test: turn the ignition to position 2 without starting the engine and watch the dashboard warning lights. The light should illuminate briefly and then go out. If it stays on, or comes on while driving in the days before your test, book a diagnostic scan and fix the fault first.
Exhaust system security and leaks
The exhaust system must be fully secure and free of leaks. Blowing joints, corroded sections, or loose mounting brackets that allow exhaust gases to escape are a major failure, particularly if fumes can enter the cabin. With the engine running, listen from outside for a hissing or blowing sound from underneath. Exhaust fumes inside the cabin confirm a leak.
Visible fluid leaks
Oil or coolant dripping onto the floor during the test is a major failure if the tester judges it to pose an environmental or fire risk. Park on a clean surface the night before and check underneath in the morning. A fresh wet patch means a leak that needs fixing.
Diesel particulate filter (DPF) failures
A blocked, removed, or non-functioning diesel particulate filter (DPF) triggers an automatic major or dangerous defect classification. Testers identify DPF tampering through the emissions opacity reading, excessive visible smoke from a diesel that should have a functioning DPF is a near-certain fail. A DPF warning light and thick black or grey smoke are the 2 signs to check before the test. DPF removal is also illegal under the Road Vehicles (Construction and Use) Regulations 1986, creating both an MOT failure and a legal problem.
Diesel variants tend to face higher emissions-related failure rates than their petrol equivalents. The Peugeot 207 diesel fails at around 35% versus 33% for the petrol version, largely because diesel emissions systems carry more components that degrade or get tampered with over time.
Bodywork, seatbelts, and other safety items
Bodywork and safety items catch many drivers off guard. Testers check areas most people never look at before booking.
Structural corrosion to sills and load-bearing panels
Not all rust fails an MOT. The rule is location: rust within roughly 30cm of any safety-critical component: suspension mounts, brake points, or seatbelt anchors, is a failure. This is the prescribed area. Surface rust on outer sills or wheel arches away from these zones is typically advisory.
To check, get underneath the car safely on ramps and inspect the sills, floor pan, and wheel arch inner edges. Press a screwdriver firmly against any suspect area. If the metal gives way, the corrosion has penetrated through that is structural and will fail. If it only flakes surface scale, it is likely advisory.
Sharp or dangerous bodywork edges
Your car's bodywork must not pose a risk to pedestrians. Torn metal, missing trim, or cracked bumpers with exposed jagged edges are a failure. Run your hand carefully along any dents, torn trim, or cracked bumper sections. If an edge feels sharp or catches your skin, a tester will flag it. Minor sharp edges can sometimes be filed smooth; anything more significant needs repair or replacement before the test.
Seatbelt condition and latch function
All seatbelts must retract smoothly, click firmly into the buckle, and release cleanly. Frayed webbing, a retractor that sticks, or a buckle that does not engage are all failures. Test each belt before the MOT: pull it fully out and let it go, it should wind back without snagging. Buckle and unbuckle it several times. Any hesitation, fraying, or failure to latch means it will not pass.
Mirrors and horn
All 3 mirrors: left wing, right wing, and interior, must be present, secure, and provide an adequate field of view. The horn must sound when pressed. Check each mirror cannot be wiggled loose and gives a clear rearward view. Press the horn: silence is a failure.
Preparing your car for not failing the MOT
A failed MOT retest costs £40–55 if you return within 10 days on the same items; leave it longer and you pay the full fee again.
Work through these 10 checks before your test:
- Lights — test headlights, indicators, brake lights, hazards, and number plate light
- Tyres, run the 20p tyre test on all 4 corners
- Brakes, test the handbrake on a safe incline
- Steering, feel for play; listen for clunks
- Wipers, run them on a wet screen; check for splits
- Windscreen, look for chips or cracks in the driver's zone
- Mirrors and horn, test all 3 mirrors and sound the horn
- Seatbelts, pull each one fully out and check it latches
- Suspension, push down on each corner; it should rebound once
- Exhaust, listen for blowing; check for fumes inside the cabin
Blown bulb or split wiper blade? Fix it yourself. Find brake noise, steering play, or suspension clunks and a professional pre-test inspection is worth booking — cheaper than a retest plus repair bill.
What does it mean for a car to officially fail an MOT?
Your car officially fails its MOT when the tester records at least 1 Major or Dangerous defect against it. Major defects mean the car poses a road safety risk and must be repaired before you drive it again. Dangerous defects are more severe still, the car cannot be driven at all until fixed. Advisory and Minor defects don't block a pass; your car receives a certificate, but those items need watching.
What to do if your car fails: retest costs, appeals, and timeline
A failed MOT means your next step depends on which defect category the tester recorded. Major and Dangerous defects make the car illegal to drive, arrange repairs or a tow immediately. A Minor defect lets you drive home, but fix it before the next test.
Retest within 10 calendar days at the same garage and you pay a discounted fee of £40–55 rather than the full MOT fee again. Wait longer, or go elsewhere, and you pay the full fee.
Driving a car with a failed or expired MOT is illegal and carries a fine of up to £1,000. An invalid MOT also voids your insurance cover, so any accident costs fall on you personally.
| Scenario | Cost |
|---|---|
| Retest within 10 days, same garage | £40–55 |
| Retest after 10 days, or different garage | Full MOT fee |
If repair costs exceed the car's current market value, scrapping is worth considering.
Final words
Most MOT failures are preventable and most cost very little to fix before test day. Lights, tyres, brakes, and suspension together account for over 70% of all failures, and you can check every one of them yourself in under 30 minutes using nothing more exotic than a 20p coin and a working pair of eyes.
Work through the 15 failure points in this guide before you book your slot. Roughly 7 in 10 cars pass on the first attempt and with a methodical pre-test check, yours has every chance of being one of them.
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