In short
An MOT grade records how a defect measured against the test standard on the day. Dangerous and major defects fail the vehicle. Minor defects and advisories do not.
Road traffic law and DVSA's roadside enforcement use their own yardsticks. Where the three can be compared, they disagree in both directions.
In the year to March 2025, tyres and brakes made up 89% of the dangerous defects recorded on cars and light vans. Below that grade the label says little about risk, and the wording of the defect says more.
Since 20 May 2018, every defect recorded at an MOT test in Great Britain has carried one of three grades, with the advisory kept as a fourth, ungraded note. Anyone reading an MOT history meets those words on every line and has to decide what weight to give them. The grades decide a test result. Vehicle condition is measured in three other ways as well: by the offences in road traffic law, by DVSA's roadside checks and by the casualty statistics. Northern Ireland's test is run separately by the DVA and is not covered here.
What each grade means on paper#
The definitions originate in Article 7 of Directive 2014/45/EU and are repeated, almost word for word, in the introduction to the MOT inspection manual.
| Grade | Definition in the manual | Result | DVSA's advice to owners in 2018 |
|---|---|---|---|
| Dangerous | Defects that are "a direct and immediate risk to road safety or having an impact on the environment" | Fail | "Do not drive the vehicle until it's been repaired." |
| Major | Defects that "may prejudice the safety of the vehicle, have an impact on the environment, put other road users at risk or other more significant non-compliances" | Fail | "Repair it immediately." |
| Minor | Defects that "have no significant effect on the safety of the vehicle or impact on the environment and other minor non-compliances" | Pass | "Repair as soon as possible." |
| Advisory | An option the tester may select when an item "is not sufficiently deteriorated to justify rejection". It is a note to the owner and has no grade. | Pass | "Monitor and repair it if necessary." |
The final column quotes the table DVSA issued in its 2018 guidance for testers. That guidance was withdrawn in June 2019, yet it remains the plainest official statement of what each grade was meant to tell an owner.
The tester does not choose the grade. Each defect wording in the testing service has carried a fixed grade since the change, and the tester's judgement lies in selecting the wording that fits the vehicle. DVSA explained beforehand that the new rules "will pre-define what is considered as 'dangerous'". A minor must be recorded wherever one applies, and an advisory need not be. The manual states: "Unlike advisory items, the use of minor defects, where appropriate, is mandatory."
Driving the vehicle after a fail#
GOV.UK allows a failed vehicle to be taken away only if the current certificate is still valid and no dangerous problem was listed. In any other case it has to be repaired first. A vehicle that may be taken away "must still meet the minimum standards of roadworthiness at all times". The stated penalty for driving a vehicle that failed on a dangerous problem is a fine of up to £2,500, a driving ban and 3 penalty points.
The law on the road does not use the grades#
The main offences concerning the condition of a vehicle make no reference to an MOT grade. Section 40A of the Road Traffic Act 1988 makes it an offence to use a vehicle on a road when its condition "is such that the use of the motor vehicle or trailer involves a danger of injury to any person". Section 41A covers any breach of a construction and use requirement "as to brakes, steering-gear or tyres".
The requirements themselves sit in the Road Vehicles (Construction and Use) Regulations 1986. Regulation 27 sets the 1.6mm tread minimum for cars and forbids the use of a tyre "not so inflated as to make it fit for the use to which the motor vehicle or trailer is being put". Regulation 100 requires a vehicle and all its parts to be "at all times" in such condition that no danger is caused, or likely to be caused, to anyone in it or on the road.
Nor does a pass establish compliance. GOV.UK tells drivers that a vehicle "can be unsafe even if you have a current MOT certificate". The MOT testing guide is more exact: the test record "relates only to the condition of testable items at the time of the test" and should not be regarded as "evidence that the vehicle fully complies with all aspects of the law on vehicle construction and use".
A defect graded minor, or noted only as an advisory, can therefore describe a vehicle that is being used unlawfully. DVSA makes the equivalent point about its own roadside notices, described in the next section: continued use of a vehicle with the defects listed on them "risks prosecution under the Road Vehicles (Construction and Use) Regulations or Road Vehicles Lighting Regulations".
How DVSA grades the same defects at the roadside#
DVSA examiners and authorised police officers who inspect a vehicle on the road work from a separate document, the Categorisation of vehicle defects (December 2024 edition). It provides for three actions. An immediate prohibition is issued where further driving "would involve a risk of injury to any person". A delayed prohibition comes into force within 10 days and allows the vehicle to be used until then. An inspection notice "is advisory only and does not in itself prevent further use of the vehicle".
The guide describes itself as "not a legal document", and we have found no DVSA document that maps its roadside actions to MOT grades. The pairing below is therefore ours. Each MOT entry is set against the nearest entry for the same component in Part 2 of the guide, which covers cars and light goods vehicles.
| Defect | MOT grade (manual reference) | Roadside action |
|---|---|---|
| Tyre tread below 1.6mm | Dangerous (5.2.3 e) | Immediate prohibition |
| Tyre obviously under-inflated | Minor (5.2.3 l) | Immediate prohibition at half the recommended pressure or less, or where steering is likely to be affected. Otherwise an inspection notice |
| Service brake efficiency below the minimum requirement | Major (1.2.2 a i) | Immediate prohibition |
| Brake pad worn below 1.5mm | Dangerous (1.1.13 a ii) | Delayed prohibition |
| Brake pad worn down to the wear indicator | Major (1.1.13 a i) | Inspection notice |
| Shock absorber showing severe leakage | Major (5.3.2 b) | Inspection notice |
| Engine malfunction indicator lamp showing a fault | Major (8.2.1.2 h, 8.2.2.2 g) | Delayed prohibition |
| Brake fluid below the minimum mark | Minor (1.1.10 d i) | Inspection notice |
| Brake fluid significantly below the minimum mark | Major (1.1.10 d ii) | Delayed prohibition |
| Brake fluid not visible | Dangerous (1.1.10 d iii) | Immediate prohibition |
The three brake fluid entries show the two scales in step. Elsewhere they diverge, and in both directions. A service brake that falls short of the required efficiency is a major at the MOT and an immediate prohibition at the roadside. A pad worn to its indicator is also a major, and at the roadside it earns an advisory notice.
Where the dangerous grade lands in practice#
DVSA's MOT testing data for classes 3 and 4 (cars, vans and passenger vehicles with up to 12 seats) records 33.1 million tests in the year to March 2025. Of those, 28.08% failed at the first attempt, and 2,551,781 tests, or 7.70%, recorded at least one dangerous defect. By our arithmetic that is a little over a quarter of initial failures.
| Defect category | Tests failing on it | Tests with a dangerous defect in it | Share of all dangerous defects |
|---|---|---|---|
| Tyres | 6.39% | 4.74% | 60.12% |
| Brakes | 6.63% | 2.58% | 29.01% |
| Suspension | 8.73% | 0.50% | 5.34% |
| Body, chassis, structure | 3.41% | 0.18% | 1.82% |
| Lamps, reflectors and electrical equipment | 10.89% | 0.13% | 1.27% |
| Steering | 1.97% | 0.10% | 0.99% |
| Noise, emissions and leaks | 3.15% | 0.03% | 0.29% |
| Visibility | 4.54% | 0.01% | 0.11% |
Lamps are the most common reason for failure and are almost never graded dangerous. Tyres are the opposite case: about three in four tests that fail on tyres include a dangerous tyre defect (4.74% of tests against 6.39%). Tyres and brakes together account for 89% of all dangerous defects recorded.
The grades are distributed quite differently on paper. The defect table that DVSA publishes with its open data, from which our MOT defects list is built, contains 1,862 defect wordings applicable to cars: 510 graded dangerous, 1,159 major and 193 minor. Suspension has 169 wordings graded dangerous and tyres have 13. In the test lane, tyres produce more than eleven times as many dangerous defects as suspension.
What the collision record shows#
Police officers attending a collision can record the factors they believe contributed to it. The Department for Transport's table RAS0701 broke vehicle defects down by type until 2023, the last year of its contributory factor system.
| Factor recorded (Great Britain, 2023) | Collisions | Of which fatal |
|---|---|---|
| Defective brakes | 553 | 9 |
| Tyres illegal, defective or under inflated | 384 | 13 |
| Defective steering or suspension | 211 | 8 |
| Defective lights or indicators | 138 | 3 |
| Any vehicle defect | 1,350 | 36 |
Brakes and tyres head the list, as they do among dangerous MOT defects, and lamps trail. A vehicle defect of any kind was recorded in 1,350 of the 66,667 collisions that had a factor recorded, which is about 2%.
The road safety factors that replaced that system no longer separate brakes from steering and suspension. For 2025 they record defective tyres in 447 collisions, 9 of them fatal, and other vehicle defects (excluding tyres and lights) in 909, of which 35 were fatal.
These figures need to be read with care. DfT's guidance states that they "reflect the reporting officer's opinion at the time of reporting and are not necessarily the result of extensive investigation". One collision may carry several factors, so the rows cannot be added together. The table covers every type of vehicle, whereas the MOT figures above cover cars and light vans. The 2025 totals also combine two recording systems that DfT says should be compared with caution.
Research on the link between test results and collisions is sparse. A TRL report for DfT in 2011 estimated that vehicle defects were "likely to be a contributory factor in perhaps 3% of accidents" and found "no established link between MOT measured roadworthiness and vehicle defects contributing to accidents, other than the common sense approach". We have found no published study that tests whether advisories or minor defects predict a later collision.
The evidence supports only a limited conclusion: at the top of the scale, the dangerous grade and the collision record point to the same two systems. Whether a particular major or minor matters on the road is a question the statistics cannot answer, which leaves the wording of the defect.
Where a grade understates the risk#
Thresholds#
A grade changes at a measured limit. A tyre with 1.6mm of tread meets the requirement and passes, and the tester may add the advisory "worn close to legal limit". A tyre measuring fractionally less is dangerous, the top grade: tread depth has no major or minor wording in between. The Royal Society for the Prevention of Accidents recommends replacing tyres "ideally as soon as they reach 3mm". A history line reading "worn close to legal limit" therefore describes a tyre that passed on the day and that RoSPA would already have had replaced.
Brake pads have a similar step. A pad worn to the wear indicator is a major. Below 1.5mm it is dangerous.
Tyre pressure#
"Tyre obviously under-inflated" is a minor, and the vehicle passes. Regulation 27 forbids the use of a tyre in that state, and the roadside guide prescribes an immediate prohibition at half the recommended pressure. In the contributory factor system that DfT used until 2023, the tyre factor in collisions was named "tyres illegal, defective or under inflated".
Brake hydraulics#
Several wordings in the brake section are minors, and the vehicle passes with each: brake fluid below the minimum mark, a flexible hose "slightly damaged, chafed or twisted", a brake pipe "inadequately clipped or supported". Each has a neighbour one wording away that fails: fluid "significantly below" the mark, a hose "excessively" damaged, a pipe "likely to become detached or damaged". Which of the two is recorded depends on the tester's judgement of degree. A brake fluid warning light that is lit is likewise a minor, whereas an ABS warning that shows a malfunction is a major.
Brake performance#
Service brake efficiency below the minimum requirement is a major. It becomes dangerous only below half the required value. The roadside guide draws no such line and prohibits immediately whenever the prescribed performance is not met.
Advisories#
Advisories carry no grade, and testers are not obliged to give them. DVSA told testers in 2015 that "in many cases testable advisories have become overused, sometimes with the same advisory being used year after year". They also age. One contributor to a MoneySavingExpert thread on buying a car with corrosion advisories put it this way: "everything is now going to be 6+ months worse than described".
Where a grade overstates the risk#
The definition of a major extends beyond safety to "an impact on the environment" and "other more significant non-compliances". A number of majors are accordingly failures on environmental or administrative grounds: an engine malfunction indicator lamp that is lit, visible smoke of any colour from a car fitted with a diesel particulate filter, exhaust noise above the permitted level, and a number plate that "does not conform to the specified requirements". An excessively corroded brake pipe carries the same grade.
Other majors are treated more lightly at the roadside than at the test. Pads worn to the indicator and a leaking shock absorber are both majors, and both receive only an inspection notice under the DVSA guide.
The top grade is itself mostly a tyre grade. Six in ten dangerous defects are tyre defects, and the remedy for a dangerous tyre line is a new tyre. It was a sound reason not to drive the car as it stood that day. It is weaker evidence about the car a buyer is looking at now.
Reading the grades in an MOT history#
- Read the wording, and the manual reference printed at the end of each line, before the grade. "Major" covers everything from a number plate to a service brake short of its required efficiency. Our MOT defects list gives every wording with its grade.
- Sort dangerous lines by section. Tyres and brakes supply 89% of them. Suspension (5.34%), body and structure (1.82%) and steering (0.99%) supply few, and a dangerous line in one of those sections merits a closer look.
- Do not discount a minor in the brake section. The wordings above sit one step from a fail.
- Follow advisories from year to year. The same advisory in successive tests may mean a fault left unrepaired, and by DVSA's own account it may also mean an overused advisory.
- Expect no grades before 20 May 2018. Older tests record a plain fail, as set out in pre-2018 vs post-2018 MOT defects.
How to read an MOT history covers passes, mileage and gaps in the record.
Dabers ANPR puts that history in front of you without leaving the listing. Right-click a car photo and the full DVSA record opens on the same page, with every test, mileage reading, advisory and failure. How it works explains the steps and pricing sets out the cost per check.
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