The most common reason cars fail their MOT
Lamps, reflectors and electrical equipment is behind 49.5% of failed MOT tests nationally — and it's one of the faults a driver can often catch before booking the test.
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“Lamps, reflectors and electrical equipment is behind 49.5% of failed MOT tests in the UK.”
Green bars mark categories with a cheap, self-checkable fix (see below).
Lamps, reflectors and electrical equipment: 49.5% of failed tests
The most frequently logged specific fault in this category is “Not working”. This is based on 52,245,925 MOT tests nationally, of which 10,843,618 failed or passed only after rectification at the test station.
The cheap fix: Check every bulb works, including number plate and fog lights — most are a £5–£15 bulb swap, no tools beyond a screwdriver.
Preventable faults you can check yourself
- Lamps, reflectors and electrical equipment (49.5% of failed tests): Check every bulb works, including number plate and fog lights — most are a £5–£15 bulb swap, no tools beyond a screwdriver.
- Tyres (24.6% of failed tests): Check tread depth (1.6mm minimum across the central three-quarters) and pressure against the door-jamb sticker — a five-minute check, no parts needed.
- Visibility (15.7% of failed tests): Top up washer fluid and check the wiper blades clear the screen without smearing — a blade replacement is typically under £10.
Every failure category, ranked
| Category | Share of failed tests | Most common specific fault |
|---|---|---|
| Lamps, reflectors and electrical equipment | 49.5% | Not working |
| Suspension | 38.1% | Ball joint excessively worn |
| Brakes | 32.4% | Less than 1.5 mm thick |
| Tyres | 24.6% | Tread depth below requirements of 1.6mm |
| Visibility | 15.7% | Does not clear the windscreen effectively |
| Body, chassis, structure | 12.9% | Constant velocity boot split or insecure, no longer prevents the ingress of dirt |
| Noise, emissions and leaks | 11.7% | Inoperative or indicates a malfunction |
| Steering | 6.8% | Ball joint has excessive play |
| Seat belts and supplementary restraint systems | 3.3% | Warning lamp indicates a fault |
| Road Wheels | 1.5% | Fixing missing |
Lamps, reflectors and electrical equipment failures by vehicle age
Raw counts of lamps, reflectors and electrical equipment failures by vehicle age band — older cars are also more numerous in the tested fleet, so this shows where the fault concentrates, not an age-adjusted rate.
| Vehicle age | Failures logged |
|---|---|
| 0–3 years | 73,742 |
| 3–6 years | 377,600 |
| 6–10 years | 1,171,523 |
| 10–15 years | 2,434,983 |
| 15+ years | 2,661,628 |
Methodology and data source
- Source: DVSA “Anonymised MOT tests and results”, data.gov.uk, under the Open Government Licence v3.0.
- Coverage: Full year 2024, test class 4 (cars), normal (initial) tests only.
- Failure categories aren't mutually exclusive — a single failed test can (and often does) have faults in more than one category, so the shares below don't sum to 100%.
- This is a whole-fleet figure, not age-adjusted — older cars fail more often overall, but the ranking of failure categories is a description of what breaks, not a comparison between groups, so no age-matching is required here.
Check your own car before it's tested
See your car's actual MOT history and advisories, and keep a record of the maintenance that heads off failures like these.
More MOT data stories
Frequently asked questions
- What is the most common reason cars fail their MOT?
- Lamps, reflectors and electrical equipment is the most common reason, present in 49.5% of failed MOT tests in the DVSA anonymised MOT tests and results dataset (52,245,925 tests nationally). The most frequently logged specific fault is "Not working".
- Can I check for common MOT failures myself before the test?
- Yes — lamps, reflectors and electrical equipment, tyres, visibility are among the most common failure categories and can typically be checked (and often fixed) yourself for little or no cost before booking an MOT.