Most Common MOT Failure Reasons in the UK

The most common MOT failure reasons UK cars face are lamps and electrical equipment, brakes, tyres, suspension, visibility and emissions. Most fails are not dramatic: a blown bulb, a worn tyre or a headlamp out of alignment is enough to fail a car, and most of these faults are cheap to prevent if you check them before the test. This guide explains each failure area, why testers record it, and how to avoid it.

Last updated: November 2026. All rules and fines in this guide are checked against GOV.UK and DVSA sources listed at the end.

A note on statistics: this guide does not quote percentage failure rates, because DVSA publishes MOT test data in releases that change over time. The ranking below follows the test areas of the DVSA MOT inspection manual, which is the document testers actually use.

How an MOT fail is recorded

An MOT test ends in a fail when the tester records a Major or a Dangerous defect. Both are fail grades, and the difference is how serious the risk is. A Major defect may affect safety, put other road users at risk, or harm the environment. A Dangerous defect is a direct and immediate risk to road safety, or has a serious environmental impact, and the car must not be driven until it is fixed. Advisory and Minor items, by contrast, still pass. GOV.UK states that a vehicle can only be driven away after a fail if its previous MOT is still valid and no Dangerous defect was listed. If you are not sure what each grade means, read how to read an MOT history report first, and what an MOT advisory means for the warnings that appear on a pass.

The six failure areas at a glance

Failure area	What the tester checks	Typical failure	Usually preventable?
Lamps and electrical	Headlamps, indicators, brake lights, reflectors and aim	Blown bulb or headlamp aim out of line	Yes, check lights and aim before the test
Brakes	Pads, discs, pipes, hoses and the parking brake	Worn pads or discs, corroded pipes, weak parking brake	Often, with regular servicing and inspection
Tyres and wheels	Tread depth, condition, size and wheel security	Tread below 1.6mm, cuts, bulges or damage	Yes, check tread and damage monthly
Suspension and steering	Springs, shock absorbers, bushes, joints and steering play	Broken spring, worn bush or excessive steering play	Partly, with servicing and by acting on advisories
Visibility	Wipers, washers, windscreen, mirrors and view of the road	Worn wiper blades, empty washer bottle, windscreen damage	Yes, often in minutes at home
Emissions and exhaust	Exhaust condition and emissions levels	Excessive emissions, exhaust leak or missing emission control	Partly, with servicing, warm engine and good fuel system health

1. Lamps and electrical equipment

Lamps are the classic avoidable fail. The tester checks that every lamp works, is the right colour, is securely fitted and is aimed correctly. A single blown brake light bulb is enough to fail the test, and headlamp aim is one of the most common single failure reasons in MOT histories. Aim matters because a headlamp that points too high dazzles other drivers, while one that points too low does not light the road properly. Aim can drift after a bulb change, a knock, or suspension work, which is why a car can pass one year and fail on aim the next.

The fix is usually a bulb or an adjustment, so this is the cheapest failure area to prevent. Before the test, switch on every light, check the indicators, brake lights, reversing light and number plate light, and ask a friend to confirm the brake lights work while you press the pedal. If a warning light is showing on the dashboard, such as an airbag or engine management light, get it checked first: the MOT inspection manual includes checks on warning lamps, and a lit warning can contribute to a failure. Our sample vehicle AB12 CDE, a Ford Focus 1.5 EcoBoost 2019 shown as illustrative sample data on the MOTBuddy MOT history checker, failed in March 2024 on headlamp aim and passed the same day after an adjustment, which is exactly how a lamp failure should end.

2. Brakes

Brakes are the most safety-critical failure area, and the one where testers are least forgiving. The MOT checks the service brake and the parking brake on a brake tester, which measures how strongly each wheel brakes and whether the effort is balanced across each axle. It also includes a visual check of pads, discs, pipes, hoses and the parking brake mechanism. Common failures are pads worn below the limit, discs scored or excessively worn, brake pipes corroded, and a parking brake that does not hold the car on the tester’s roller.

Brake wear is gradual, which is why the MOT history matters so much here. A brake advisory in one year that becomes a brake failure the next year is a familiar pattern in MOT histories, and it is entirely avoidable if the advisory is acted on. If your car pulls to one side when you brake, if the pedal feels soft or spongy, or if you hear grinding, do not wait for the MOT to tell you there is a problem. Get it checked straight away, because brake problems are safety problems, not paperwork problems. A Dangerous defect on a brake, such as a brake pipe at risk of bursting, means the car must not be driven at all.

3. Tyres and wheels

Tyres fail for two main reasons: not enough tread, and damage. The legal minimum tread depth for cars is 1.6mm across the central three-quarters of the tread, around the whole tyre. Testers measure the tread at several points, because a tyre can be legal in one place and below the limit in another, usually because of uneven wear from poor wheel alignment or worn suspension. Damage is the other cause: cuts, bulges and lumps in the sidewall, exposed cords, or a tyre that is the wrong size or type for the vehicle. A tyre pressure monitoring system, where fitted, is also checked, and a warning light can be a failure item.

Tyres are another failure that is easy to prevent. Check the tread with a 20p coin: the outer band of the coin is about 2mm wide, so if you can see the band when the coin is pushed into the tread, the tyre is close to the limit and needs replacing soon. Check the pressures against the handbook or the sticker on the door frame, and look at the sidewalls for cuts and bulges when you check the tread. AB12 CDE’s most recent test, in March 2026, passed with a single advisory for the front-left tyre worn close to the legal limit, which is the warning that comes before a tyre failure, not the failure itself. The owner who replaces that tyre now will not be the owner who fails on it next year.

4. Suspension and steering

Suspension and steering failures are common on older and higher-mileage cars, because these parts work hard on every journey and wear out gradually. The tester checks springs, shock absorbers, bushes, ball joints and the steering system, looking for broken springs, leaking shock absorbers, excessive play in joints, and steering that is stiff, loose or noisy. A broken coil spring is a common failure on cars that are a few years old, and it often goes unnoticed by the driver until the tester finds it, because the car can still feel normal to drive.

Warning signs include a car that bounces after a bump, knocks over uneven roads, sits lower on one corner, or has tyres wearing unevenly. As with brakes, the MOT history gives you the early warning: a suspension advisory one year often becomes a suspension failure the next. Fix worn bushes and joints when they are advisories, and you avoid both the failure and the extra tyre wear that worn suspension causes. Steering failures are rarer, but they are taken very seriously, because a steering fault can be Dangerous, and a Dangerous steering defect means the car must not be driven.

5. Visibility: wipers, washers, windscreen and mirrors

Visibility failures are the most frustrating of all, because they are usually free to prevent. The tester checks that the wipers clear the windscreen, that the washers work and the bottle is not empty, that the windscreen is not damaged in the driver’s view, and that the mirrors are secure and undamaged. A windscreen chip is a fail only if it is in the driver’s line of sight, specifically in the area swept by the wipers directly in front of the driver, and it is larger than 10mm. Elsewhere in the swept area the limit is 40mm, and damage outside the swept area is not a failure item, although it can still be recorded as an advisory.

The prevention routine takes two minutes: lift the wipers and check the rubber is not split or perished, top up the washer bottle, and check the windscreen for chips. Replace wiper blades once a year, or as soon as they smear or judder, because a pair of wiper blades costs very little compared with a failed test and a second trip to the test station. That second trip matters: if the car fails, the retest rules mean a partial retest is free only if the car is repaired and returned to the same test station within 10 working days for certain items, so even a small failure wastes time as well as money.

6. Emissions and exhaust

Emissions failures are the failure area that owners understand least, because the car can feel fine while it fails. The tester measures the exhaust gases against the limits for the vehicle’s age and fuel type, and checks the exhaust system for leaks and for the presence of emission control equipment such as the catalytic converter or diesel particulate filter. On diesel cars, a smoke test measures how much soot the exhaust produces. A car can fail on emissions for a long list of reasons, including a tired oxygen sensor, a failing catalytic converter, a blocked diesel particulate filter, or simply an engine that has not been serviced properly.

Some useful preparation helps. Take the car for a proper drive before the test so the engine and the exhaust system are fully warm, because cold engines produce higher emissions, and avoid a test on a car that has spent months doing only short trips. Keep up with servicing, because old oil, clogged air filters and worn spark plugs all make emissions worse. If your car does fail on emissions, do not guess: ask the garage to diagnose the cause, because replacing parts at random is expensive and may not fix the fault. Diesel owners should also know that a diesel particulate filter warning light, or evidence that the filter has been removed, is a failure item under the MOT inspection manual.

Worked example: a car that failed in several areas (illustrative sample data)

CD34 EFG, the Vauxhall Astra 1.2 Turbo 2018 shown as illustrative sample data on the MOTBuddy MOT history checker, shows what a multi-area failure pattern looks like. It failed in March 2024 on emissions, in March 2025 on headlamp aim and a worn tyre, and in March 2026 on worn brakes and a corroded exhaust, with no pass recorded after the 2026 test. Each failure is from a different area of the table above, which tells you the car has not been maintained between tests: problems have been left until the MOT forces the issue, and each year a new system has reached the point of failure. That is the record to watch for when you check a car’s MOT history before buying: a single failure is normal, but a different failure every year is a maintenance record, not bad luck.

What happens if your car fails

If your car fails, the tester will give you a list of the failure reasons and their grades, and you will need a retest after the repairs. GOV.UK sets out the retest rules: a partial retest is free if the vehicle is left at the test station for repair, or returned to the same station within 10 working days, for certain items. You can only drive the car away after a fail if the old MOT is still valid and no Dangerous defect was recorded. If a Dangerous defect was recorded, or the old MOT has expired, the car must stay off the road until it is fixed and passes. The maximum fee a test station can charge for a car MOT is 54.85 pounds, and no VAT is charged on the test fee, although repairs and retests can still cost money, so preventing a fail is usually cheaper than paying for one.

Nine checks to do before your MOT

• Switch on every light, including brake lights, indicators and the number plate light.
• Check tyre tread with a 20p coin and look for cuts or bulges in the sidewalls.
• Top up the washer bottle and replace wiper blades that smear or judder.
• Test the horn, handbrake and seatbelts.
• Check the windscreen for chips in the driver’s view.
• Look under the car for leaks and check fluid levels.
• Make sure the number plates are clean, legible and secure.
• Take the car for a proper drive so the engine is fully warm.
• Act on last year’s advisories before the test, not after it.

Related guides

If you are buying a car, read how to read an MOT history report to spot these failures in the record, learn what an MOT advisory means for the warnings that come before a fail, and read Dangerous MOT defects explained for the most serious grade.

Sources

• GOV.UK, Getting an MOT: MOT test result and MOT costs: gov.uk/getting-an-mot
• GOV.UK, Check the MOT history of a vehicle: gov.uk/check-mot-history
• DVSA, MOT inspection manual: gov.uk MOT inspection manual