Why do cars fail the MOT most often in the UK?

The most common failure categories, ranked

These are the five categories DVSA records most often, taken from its own figures for classes 3 and 4, which cover cars, for the 2024/25 testing year in Great Britain. There were 35,229,047 tests in Great Britain across all classes that year.

These shares add up to more than the 28.08% initial failure rate. One car can be recorded against several categories at the same test — DVSA logged an average of 2.44 defects per initial failure — and the five rows above are not the full list of categories DVSA publishes.

Why tyres matter more than their ranking suggests

Ranking failures by how often they appear understates tyres badly. A blown bulb and a tyre below the legal tread depth both count as one defect, but only one of them is a reason to stop driving. DVSA grades the most serious findings as dangerous, meaning a direct and immediate risk to road safety or a serious impact on the environment, and tyres dominate that grade.

• Tyres: 60.12% of all dangerous defects
• Brakes: 29.01% of all dangerous defects
• Suspension: 5.34% of all dangerous defects

At least one dangerous defect was recorded in 7.70% of tests. So the lighting category is the one you are most likely to meet, and the tyre category is the one most likely to mean the car was genuinely unsafe on the road it arrived on.

What the 28.08% failure rate does and does not mean

DVSA recorded an initial failure rate of 28.08% for classes 3 and 4 in 2024/25. That number is a national rate: it describes the whole population of initial tests carried out in Great Britain that year, across every age, mileage and condition of vehicle presented.

It is not the chance that a given car will fail. A three-year-old car on its first test and a fifteen-year-old car on its twelfth sit inside the same 28.08%, and nothing in that figure tells you which one you are looking at. It also counts initial tests only, so a car that fails, is repaired and passes a retest still sits on the failing side of it. Treat it as context for how common failure is in general, never as a probability attached to one registration.

Minor, major and dangerous defects

Defects found at the test are graded, and the grade decides the result:

• Minor: the car passes. The defect is recorded on the certificate.
• Major: the car fails.
• Dangerous: the car fails, and the defect represents a direct and immediate risk to road safety or a serious impact on the environment.

An advisory is not a failure at all. It is a note that something is wearing and may need attention before the next test — brake pads getting thin, or tyres near, but not below, the limit. On a used car, a run of repeated advisories for the same item across several years is worth more to you than any single pass certificate, because it shows what has been left alone. We cover this in detail in what an MOT advisory means.

The maximum fee a garage in Great Britain may charge for a class 4 test is £54.85. It is a maximum rather than a set price, no VAT is charged on it, and it has not changed since 2010.

Northern Ireland is tested under different rules

Everything above comes from DVSA, which covers England, Scotland and Wales. Testing in Northern Ireland is run by the DVA, and the rules differ in ways that matter when buying:

• The first test is due at four years, not on the third anniversary.
• A full test is £38.00 and a retest £29.50. Like the Great Britain fee, these are maximums and carry no VAT.
• Public test history goes back only to 2017 in Northern Ireland, against 2005 in England, Scotland and Wales.

That last point is the practical one. Because the record in England, Scotland and Wales runs back to 2005, and cars are not tested before their third birthday, almost every used car sold there arrives with its complete published test history attached. In Northern Ireland the record starts in 2017, so a car first tested before then is missing its early results whatever its age.

What to check before you buy a used car

The failure categories tell you where to look. Lighting and electrical faults are cheap and visible: walk round the car with the lights, indicators and brake lights on. Tyres are the ones to take seriously, because they are where the dangerous defects are, and they are checkable in a couple of minutes on the forecourt.

The published test history is the strongest free evidence available on a used car. Use our MOT check tool to see when a car's next test is due, and read our guide to the most reliable used cars in the UK for what tends to go wrong on particular models. Unfamiliar terms on a certificate are explained in the glossary.