What fails an MOT? Failure categories explained
Since May 2018, MOT failures have been classified into three categories: dangerous, major, and minor. Understanding which category a defect falls into determines whether you can drive the car away immediately, need to arrange repairs, or receive a note to monitor before the next test.
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MOT failure categories: dangerous, major, and minor
The current MOT test classifies all defects into one of three types. A dangerous defect is an immediate failure - the vehicle poses a risk to road safety and must not be driven away. A major defect is also a failure, but the car may be driven away if the previous MOT certificate is still valid, or driven to a place of repair if the certificate has already expired. A minor defect is a pass with an advisory note - the item is recorded for the driver to monitor but does not cause the test to fail.
This three-category system was introduced in May 2018 in line with updated European testing standards and replaced the older pass-or-fail system.
What is a dangerous MOT defect?
A dangerous defect is one that the tester has assessed as posing a direct and immediate risk to road safety or the environment. If your car receives a dangerous defect, it has failed the test and must not be driven away. Examples include total brake failure, severely cracked or deformed suspension components, or severe structural corrosion affecting safety-critical areas. You will need to arrange recovery or have the car repaired on-site.
What is a major MOT defect?
A major defect is a failure but is less immediately dangerous than a dangerous finding. If your previous certificate is still valid, you may drive the car away to get it repaired. If the previous certificate has expired, you can only drive the car to a place of repair and must not use it for general driving. Major defects are the most common cause of MOT failures. Examples include tyres with tread below the 1.6mm legal minimum, a cracked windscreen in a critical zone, worn brake pads below the minimum thickness, and faulty headlights.
What is an MOT advisory?
An advisory is not a failure - it is a note attached to a passed test flagging an item approaching but not yet at the legal limit. Advisories are not requirements but should be taken seriously. A common example is brake pads noted as wearing and due for monitoring before the next test. Acting on advisories promptly reduces the chance of a failure at the following test.
Common MOT failure reasons
According to DVSA data, the most common reasons for MOT failures in the UK are:
- Lighting and signalling - bulbs, wiring, and adjustments account for a large proportion of all failures
- Suspension - worn or damaged components
- Brakes - brake pad thickness, disc condition, and brake balance
- Tyres - tread depth below 1.6mm, bulges, cuts, or mismatched tyres on the same axle
- Windscreen - chips or cracks in the driver's critical eyesight zone
- Emissions - particularly on older diesel vehicles and cars with engine management faults
- Engine management warning light - an illuminated MIL (Malfunction Indicator Lamp) is an automatic failure
Running through a pre-MOT checklist before the test lets you spot many of these items yourself - a blown bulb, worn wiper blade or tyre below the legal limit costs far less to fix before the appointment than a retest fee.
Can you drive your car after a failed MOT?
The answer depends on the type of defect and whether your old certificate is still valid. If the failure was for a dangerous defect, the car must not be driven. If the defect is major and your old certificate is still in date, you may drive the car to arrange repairs. If the old certificate has expired, you may only drive directly to a garage for repairs. If the car fails with minor defects only, it has in fact passed - minor defects result in a pass with advisories.
If your car is off the road while repairs are sorted, our guide to transport options when your car is in for repairs explains your options, including how temporary car insurance lets you borrow another vehicle without affecting the owner's policy.
The full process once you have the result - from reading the VT30 to navigating the retest - is covered in our guide to what to do after an MOT failure.
Emissions and warning lights at the MOT
The MOT checks emissions against limits set for the vehicle's age and fuel type. Petrol cars are tested for hydrocarbons and carbon monoxide output; diesel cars undergo a smoke opacity test. An engine management warning light (sometimes called the malfunction indicator lamp or MIL) that remains illuminated after startup is treated as a major defect and constitutes an automatic failure - because the light signals an unresolved fault detected by the vehicle's own systems.
If your engine management light comes on before a test, it is worth having the fault code read at a garage or using an OBD reader before the appointment. The codes can range from a loose fuel filler cap - an inexpensive fix - to a more significant engine issue. Knowing the code in advance tells you whether a straightforward repair will resolve it or whether deeper mechanical work is needed. Arriving at an MOT with a dashboard warning light on is an avoidable failure, particularly when a code reader costs less than the retest fee.
What happens after an MOT failure?
After a failure, you can have the defects repaired and return for a partial retest, or have repairs done elsewhere and book a full retest. Many garages offer a free partial retest if the car is returned within a set period - often the same day or within ten working days. If repairs are done elsewhere, a full retest fee applies.
Frequently asked questions
If my car fails its MOT, is the old certificate still valid?
If your car fails its MOT before the existing certificate expires, the old certificate remains valid until its expiry date. During that period you can drive the car normally - though you should arrange repairs. Once the certificate has expired, the car can only be driven to a place of repair.
Can a car fail an MOT on just one minor issue?
No. Minor defects result in a pass with an advisory note, not a failure. Only major and dangerous defects cause an MOT failure. If the only issues found are minor, the test result is a pass.
What is the difference between a major and a dangerous defect?
A dangerous defect means the vehicle poses an immediate road safety risk and must not be driven. A major defect means the vehicle has failed the test but can be driven away if the previous certificate is still valid, or driven to a place of repair if not.
What is a free retest and when am I entitled to one?
A free partial retest covers only the items that caused the failure, and is offered by many stations if the car is repaired and returned within a set period - typically the same day or within ten working days. If you have the car repaired elsewhere or do not return in time, a full retest at the standard fee applies.
Can I appeal an MOT failure?
Yes. You can request an appeal inspection if you disagree with the outcome. Contact the DVSA within 14 days of the test. If the appeal is upheld, the inspection fee is refunded.
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