Dangerous, Major, Minor and Advisory MOT Defects Explained

Before May 2018 an MOT had two outcomes that mattered: pass or fail, with advisory notes attached. Since then testers have graded every fault they find into one of four tiers, and the wording of those tiers has real legal and practical consequences. Two of them fail the test. One of those two means you must leave the car where it stands. The other two appear on a pass certificate but are recorded permanently and publicly.

This guide sets out what each grade means, what you may and may not do with the vehicle afterwards, and why the same worn component can be graded differently from one year to the next.

The four grades at a glance

The two things people get wrong most often are at opposite ends of the scale. First, a minor defect is a pass, not a fail — the name misleads. Second, a dangerous defect is not a suggestion; it is the point at which the tester is telling you that continued use puts people at risk, and driving on is a separate offence from having no MOT.

Dangerous defects

A dangerous defect means the tester has identified a fault presenting a direct and immediate risk to road safety or a serious environmental impact. The certificate you receive is a refusal, and it will state clearly that the vehicle should not be driven until the fault is repaired.

Typical examples:

• A tyre with the cords or ply exposed, or a bulge in the sidewall.
• A brake pipe corroded to the point of imminent failure, or a fluid leak from a brake component.
• A steering or suspension component so worn that it could separate.
• Structural corrosion severe enough to compromise a suspension mount or seatbelt anchorage.
• A wheel not securely attached, or a badly cracked wheel.
• A fuel leak.

The legal position on driving away

This is where the grading system has teeth. Under road traffic law it is an offence to use a vehicle on a road in a dangerous condition, and that offence exists entirely independently of whether the vehicle has a valid MOT certificate. So the fact that your old certificate still has two months to run is irrelevant: the tester has documented that the car is dangerous, and that documentation is now on a public record with a date on it.

Using a vehicle in a dangerous condition can carry a fine of up to £2,500, three penalty points and, in serious cases, disqualification. The insurance dimension is arguably worse. If you drive away, crash, and an insurer establishes that a test centre had recorded a dangerous defect that morning, your prospects of a successful claim are poor.

Your options are to have the repair carried out at the test centre, arrange recovery to a garage of your choice, or arrange for the repair to be carried out where the vehicle stands. What you cannot do is drive it, including "just around the corner".

Major defects

A major defect is a fault that may affect the vehicle's safety, put other road users at risk, or have a significant environmental impact. It is a straightforward failure and must be repaired before the vehicle can pass.

Most failures are major defects. Common examples include:

• Brake efficiency below the required minimum, or excessive imbalance across an axle.
• Tyre tread below 1.6mm across the central three-quarters of the tread.
• A headlamp not working, or aimed incorrectly.
• Excessive play in a ball joint, track rod end or wheel bearing.
• An illuminated airbag, ABS or engine management warning lamp.
• Windscreen damage over 10mm in the driver's zone A, or over 40mm elsewhere in the swept area.
• Exhaust emissions above the applicable limit.
• Any visible smoke, of any colour, from a diesel fitted with a factory particulate filter.

What you may do after a major-defect failure

Here the rules are more permissive than people expect, and the distinction rests entirely on your existing certificate.

If your previous MOT certificate is still valid, it remains in force until its expiry date. A failure does not retroactively cancel it. You may legally drive the car — provided, of course, that it is not actually in a dangerous condition and that the specific defect is not itself a separate offence. Bald tyres are a good illustration: the tyre may have been graded major rather than dangerous, but driving on a tyre below 1.6mm is an offence in its own right carrying a fine and three penalty points per tyre.

If your previous certificate has expired, you may only drive the vehicle to a pre-arranged repair appointment or to a pre-booked MOT test. Nothing else. Driving without a valid MOT otherwise risks a fine of up to £1,000.

That difference is worth planning around. Getting the test done a few weeks before your certificate expires gives you a legal window in which to shop around for repairs rather than accepting the first quote you are offered.

Minor defects

A minor defect is a fault with no significant effect on the safety of the vehicle or on the environment. The vehicle passes, and the defect is listed on the certificate with a note to repair it as soon as possible.

The category was introduced in May 2018 to capture faults that previously sat awkwardly between an advisory and a failure. Examples include a small exhaust leak that does not affect the effectiveness of the silencer, a slightly damaged but functional lamp lens, a minor fluid leak, or a windscreen wiper that is deteriorating but still clears the screen.

Two practical consequences follow.

First, minor defects are published. They go onto your vehicle's permanent public MOT record alongside the pass, which means anyone who later looks up the registration can see them. That is not a reason to panic, but it is a reason to fix them — an unresolved minor defect appearing on three consecutive certificates says something about how the car has been maintained, as our guide to red flags in an MOT record explains.

Second, a minor defect will often be a major one next year. The threshold between the two is frequently a matter of degree, and nothing about passing the test makes the component stop wearing.

Advisories

An advisory is not a defect at all in the formal sense. It is a note from the tester that a component is deteriorating, or that something needs monitoring, without any current breach of the standard.

The classic advisory is a tyre measured at 2mm — perfectly legal, well above the 1.6mm minimum, and clearly not going to last another year. Others include light surface corrosion to the underbody, brake pads approaching the end of their useful material, slight play in a joint that is still within tolerance, and oil seepage that is not yet a leak.

Advisories are the most useful part of the certificate and the most widely ignored. They are a professional prediction of your next repair bill, written by someone who has just had the car on a ramp. Acting on them at your own convenience is always cheaper than acting on them under the pressure of a failed test.

Why the same fault is graded differently on different tests

This is the most common source of frustration, and the explanation is usually mundane rather than sinister.

Many defects are graded on measurement, not on presence

A large share of steering, suspension and brake defects are assessed against a numerical threshold. The tester levers a component and judges the movement; below a defined amount it is an advisory, above it a major defect. A ball joint with movement sitting a fraction under the threshold will be advised. The same joint a year later, with slightly more movement, fails. Nothing dramatic happened between the two tests — the component simply crossed a line.

The same applies to brake performance. Efficiency and imbalance are measured on a roller brake tester, and a car that recorded a marginal pass can fail the following year with less pad wear than you would expect, because a partially seized calliper has shifted the balance.

Judgement is genuinely involved

DVSA sets the standard, but applying it to a real car involves assessment. "Excessive" corrosion, a windscreen chip right on the boundary of zone A, a slightly discoloured lamp lens, a seat belt with light surface fraying — these are marginal calls, and two competent testers can reach different conclusions on the same vehicle. This is not a flaw in the system so much as an inherent feature of any inspection carried out by people.

Conditions on the day change the outcome

Brake performance depends on how warm the brakes are, whether the discs are lightly corroded from standing, and how the vehicle is loaded. Emissions results depend on whether the engine reached full operating temperature. A diesel driven three miles from cold to the test centre can produce a worse smoke reading than the same car after a motorway run.

The standard itself changes

The testing standard is updated periodically. Items have been added over the years — daytime running lamps, reversing lamps, tyre pressure monitoring, the diesel particulate filter rules, and the visible-smoke rule for DPF-equipped diesels among them. A car that passed comfortably in one year can fail on something that was not tested at all in the year before. The full current scope is set out in what is checked on an MOT.

Reading your certificate

A pass produces a certificate listing any minor defects and advisories. A failure produces a refusal notice listing every dangerous and major defect, plus any minor items and advisories found. Both go onto the public record.

Work through the document in this order:

1. Check for the word "dangerous". This determines whether you can move the car at all.
2. Check the expiry date of your existing certificate. This determines what you may legally do after a major failure.
3. Separate expensive failures from cheap ones. Bulbs, wipers, washer fluid, plates and mirrors are usually trivial. Brakes, suspension, corrosion and emissions are not.
4. Read the advisories. These are next year's failures, and you have twelve months to deal with them at your own pace.
5. Look up anything you do not understand. Defect wording is standardised and often opaque; entries like brake performance below requirements or suspension arm bush worn mean something specific.

Retests: what you pay and when

The retest rules are more generous than most drivers assume, and knowing them before you leave the test centre can save you the price of a whole test.

• Leave the vehicle at the test centre for repair, and the partial retest is free.
• Take the vehicle away and bring it back before the end of the next working day, and the retest is free for a specified list of straightforward items — lamps, wipers, mirrors, registration plates, seat belt condition, the fuel filler cap, the horn and several others.
• Return within 10 working days for a partial retest covering only the failed items, and a reduced fee may apply at the centre's discretion.
• Return after 10 working days, and you pay for a complete new test.

The maximum fee for a full class 4 test — most cars and light vans — is £54.85. That cap is set by DVSA and a centre cannot charge more for the test itself, though there is no cap on what it charges for repairs.

If you think the grading is wrong

Start with the test centre. Ask the tester to show you the defect on the vehicle and explain which part of the standard it breaches. A competent tester will do this readily, and a large proportion of disputes end here, either because the fault becomes obvious or because a marginal call is reconsidered.

If that does not resolve it, you can appeal to DVSA. The appeal is made on form VT17, and DVSA asks for it within 14 working days of the test. Crucially, do not have the disputed work carried out before the appeal is decided — DVSA needs to inspect the vehicle in the condition it was tested in, and repairing it destroys the evidence. Note that a fee may apply, refundable if your appeal succeeds.

You can also complain if you believe a vehicle was passed when it should not have been, which matters if you have just bought a car with a suspiciously fresh certificate.

The practical summary

Two questions resolve almost every situation:

Did anything come back as dangerous? If yes, the car does not move under its own power until it is repaired, regardless of what your old certificate says.

Is your existing certificate still valid? If yes, and the failures are major rather than dangerous, you have breathing room to get quotes and choose where the work is done. If no, you can drive only to a booked repair or a booked test.

Everything else is a question of cost and timing. Fix the majors because you must, fix the minors because they are cheap now and expensive later, and treat the advisories as a written forecast of the year ahead. Doing that consistently is also what produces the clean, uneventful MOT record that makes a car straightforward to sell, which is exactly what a careful buyer looks for when checking a used car before buying.