The Most Common MOT Failures (And How to Avoid Them)
Roughly one car in five fails its MOT — the pass rate across 57.6 million recorded tests sits at about 78.3%. The failures are not spread evenly. Four categories account for the overwhelming majority:
| Category | Share of failures | Typically preventable? |
|---|---|---|
| Lighting and signalling | ~30% | Almost entirely |
| Suspension | ~20% | Rarely |
| Brakes | ~18% | Sometimes |
| Tyres | ~12% | Almost entirely |
The headline is worth sitting with: the single biggest cause of MOT failure is blown bulbs, and it costs a few pounds to prevent.
1. Lighting and signalling — around 30%
Nearly a third of all failures, and the great majority are bulbs that had blown before the test and nobody noticed.
The ones people miss are the ones you cannot see from the driver’s seat: number plate lights, the rear fog lamp, reversing lights, and one of a pair of brake lights. A single failed brake bulb is a fail, and you will never spot it while driving.
How to avoid it: ten minutes with somebody to help. Walk round with the lights on, then sidelights, then main beam, then indicators and hazards, then have someone press the brake pedal and select reverse while you look. Check the number plate lights specifically. Headlight aim also fails cars fairly often — that one needs a beam setter, so it is worth checking if the car has had front-end work or new bulbs fitted.
2. Suspension — around 20%
The second biggest category and the least preventable, because most of it is wear you cannot see.
Common failures are worn shock absorbers, cracked or broken coil springs, worn ball joints and track rod ends, perished bushes, and corroded or damaged suspension arms. In Birmingham this category is inflated by road surfaces — potholes, speed humps and kerbing take a real toll, and dampers degrade so gradually that owners adapt without noticing.
How to avoid it: the bounce test tells you something. Push down hard on one corner of the car and let go — it should return to level in one movement. If it keeps bouncing, the damper is tired. Also look for uneven or scalloped tyre wear, and listen for knocking over bumps. Any of those is worth having checked before the test rather than after.
3. Brakes — around 18%
Brake failures split into two kinds. Some you can feel: grinding, a long pedal, pulling to one side. Others you cannot, and those are the ones that catch people.
The test puts the car on a roller brake tester and measures both overall braking efficiency and the balance between the two wheels on each axle. A partly seized calliper means one side brakes harder than the other, and the machine sees an imbalance that no driver would notice. Corroded discs, worn pads, a stretched handbrake cable and leaking or corroded brake lines all appear here too.
How to avoid it: take noises seriously. Squealing is usually the wear indicator doing its job; grinding means the material has gone and you are now damaging the discs. A handbrake that needs more clicks than it used to is worth adjusting before the test.
4. Tyres — around 12%
Almost entirely preventable, and it is usually not overall tread depth that fails a car — it is one edge.
The legal minimum is 1.6mm across the central three-quarters of the tread around the whole circumference. A misaligned wheel wears the inner shoulder while the rest of the tyre looks fine, and the inner shoulder is the part you cannot see without turning the wheel on full lock. Sidewall bulges, cuts and exposed cord are outright failures regardless of tread.
How to avoid it: the 20p test — insert a 20p coin into the main grooves, and if the outer band of the coin is visible you are at or near the limit. Do it at several points around each tyre and check the inner edge with the wheels turned. If one edge is wearing faster, get the alignment checked, or a new tyre will do exactly the same thing.
The failures nobody expects
Beyond the big four, a steady trickle of cars fail on things that take seconds to fix: windscreen washers that do not work or a bottle that is empty, wiper blades that smear, a horn that does not sound, a mirror that is cracked or missing, a registration plate that is damaged or unreadable, and windscreen chips in the area directly in front of the driver, where the size limit is stricter than elsewhere.
Anything the tester notes but passes becomes an advisory, which is worth reading rather than filing. Also increasingly common: a dashboard warning light. An illuminated airbag, ABS, brake or engine management light is a failure in itself, regardless of whether the car drives normally.
How age changes your odds
Failure rate climbs steadily with age, and it is useful to know roughly where your car sits:
- 3–4 years old: around 13% fail
- 10 years old: around 30% fail
- 15 years old: around 42% fail
None of that is a reason to give up on an older car. It is a reason to have one checked before the test rather than hoping.
How much does it cost to fix?
The average repair bill following an MOT failure runs to roughly £140–£170, but the spread is enormous. A bulb might be £5 fitted. A pair of wiper blades, £20. Brake pads and discs on one axle, £200–£320. A pair of shock absorbers, £150–£400. Two tyres, £120–£250.
The point of the ten-minute pre-check is that it removes almost all of the cheap failures, which are also the most common ones.
When should you call a garage?
Do the lights, tyres, wipers, washers and horn yourself — that is most of the risk gone for the price of a bulb. Our pre-test checklist walks through it.
Book a pre-test check if last year’s certificate carried advisories, if the car is over ten years old, if anything knocks or bounces, or if a warning light is showing. Those are the categories you cannot assess from the driveway, and finding out on the test day leaves you with a failed car and a deadline.
We are a DVSA-approved test centre and a repair garage, so we can check, test and fix. Our Birmingham MOT centre is open seven days a week.
Frequently asked questions
What is the single most common MOT failure?
Lighting and signalling, at roughly 30% of all failures — and most of it is blown bulbs that nobody noticed. The ones people miss are the ones invisible from the driver's seat: number plate lights, the rear fog lamp, reversing lights and one of a pair of brake lights. Ten minutes with someone helping you check removes most of that risk.
What percentage of cars fail their MOT?
About one in five. The pass rate across 57.6 million recorded tests is roughly 78.3%. It varies sharply with age though — around 13% of cars fail at three to four years old, about 30% at ten years, and around 42% at fifteen.
Will a warning light on the dashboard fail an MOT?
Yes, for several systems. An illuminated airbag, ABS, brake or engine management light is a failure in its own right, regardless of whether the car drives perfectly well. It is worth getting a light diagnosed before the test rather than hoping the tester overlooks it.
Can my tyres fail even if the tread looks fine?
Yes, and this is the common trap. A misaligned wheel wears the inner shoulder of the tyre while the rest looks healthy, and that inner edge is the part you cannot see without turning the wheels on full lock. Sidewall bulges, cuts and exposed cord are outright failures regardless of how much tread is left.
How much does it cost to fix an MOT failure?
The average is roughly £140 to £170, but the spread is huge. A bulb might be £5 fitted and wipers £20, while brake pads and discs on one axle run £200 to £320 and a pair of shock absorbers £150 to £400. The cheap failures are also the most common ones, which is why a pre-check pays for itself.
Want us to take a look?
Ring us and describe what the car is doing. We’ll tell you what it’s likely to be and roughly what it will cost before you bring it in.