The short answer
Seat belt and airbag faults are among the least common reasons a car fails its MOT, but they are the ones that matter most when the back seat is full. In tests carried out 2021 to 2025, an airbag warning lamp showing a fault failed about 1 in 85 first tests on cars aged 15 and over (1.2% of 31,405,150 tests). On cars aged 3 to 5 the same item failed about 1 in 800 (0.1% of 33,793,352 tests).
Before a long drive this half term: start the car and watch the airbag lamp go out, pull every belt out fully and let it retract, click every buckle, and look at the floor and sills near the belt mountings on an older car. Each of those is a thing the tester checks.
What fails, at what age
The MOT manual groups seat belts, their mountings and the airbag system together, which is why the airbag lamp sits in this family. Each cell below is the share of all first tests in that age band that failed with the item, pooled across 2021 to 2025. A dash means the item was outside the eight most recorded for that band.
| Item recorded | 3-5 years | 6-9 years | 10-14 years | 15 and over |
|---|---|---|---|---|
| Airbag warning lamp shows a fault | 0.1% | 0.2% | 0.6% | 1.2% |
| Structure within 30 cm of a belt mounting weakened | - | - | 0.1% | 0.9% |
| Buckle not working | 0.1% | 0.1% | 0.1% | 0.2% |
| Belt not working as intended | under 0.1% | 0.1% | 0.1% | 0.2% |
| Retractor defective | under 0.1% | under 0.1% | under 0.1% | 0.1% |
| Buckle missing | under 0.1% | under 0.1% | under 0.1% | 0.1% |
Two things drive the rise. The airbag lamp is an electrical fault that accumulates with time: a connector under a seat, a sensor, a clock spring in the steering wheel. The mounting item is corrosion. The tester checks the metal within 30 centimetres of every belt anchorage, and on cars past fifteen that is where rust has had the longest to work.
Looked at by the year a car was first used, the pattern is the same. Cars first used in 2006 recorded a seat belt or airbag fail in 1.4% of first tests (4,746,066 tests). Cars first used in 2010 recorded 0.8%, 2014 cars 0.4%, and 2017 and 2018 cars 0.2%.
The one figure that goes the other way
As a share of all fails, rather than all tests, seat belts and airbags are more prominent on the newest cars than on middle-aged ones. On cars first used in 2021, 3.2% of fails involved this family (182,783 fails); on 2016 and 2017 cars it was 1.7%; on 2006 cars 3.8%. That is not because young cars have belt problems. It is because young cars fail so rarely that the few faults they do have, an airbag lamp among them, make up a bigger slice of a small number. Read the share of tests for how likely a fault is; read the share of fails for what a fail is made of.
Why this matters this week
Half term in most of England and Wales is next week, and the clocks go back this Sunday, so many of those journeys will end in the dark. The law is clear on who is responsible. You must wear a seat belt if one is fitted, and you can be fined up to £500 if you do not. Children must use the correct child seat until they are 135 centimetres tall or their 12th birthday, whichever comes first, and the driver is responsible for children under 14. The rules are on GOV.UK seat belt law and GOV.UK child car seat rules. A belt that does not retract, or a buckle that does not latch, means a seat you cannot legally use.
What to check
- The airbag lamp. Turn the ignition on. The lamp should light and go out within a few seconds. A lamp that stays on, or flashes, is a Major defect at the test. A lamp that shows the passenger airbag is switched off is not a defect, and the manual says so.
- Every belt, fully out. Pull each belt all the way out, look along the webbing for cuts, fraying or stretched patches, then let it go and watch it retract fully on its own.
- Every buckle. Click each one in and release it. A buckle that is stiff, sticks, or releases under a tug is a fail.
- The mountings, on an older car. Lift the carpet at the floor anchorages and look at the sill where the lower mounting bolts in. Soft, flaking or holed metal near a mounting is the item that fails 0.9% of tests on cars over fifteen.
- The child seat. Check the belt routes through the seat as the seat's label shows, and that an ISOFIX seat is latched on both arms.
- Your history. Look up past advisories on GOV.UK check MOT history. A corrosion advisory near a belt mounting is a warning of next year's fail.
If a belt or buckle does fail the test, seat belts are on the list of items that can be retested free before the end of the next working day at the same centre, as set out on GOV.UK retests.
What this does not mean
These are fleet figures. A 1.2% rate on cars over fifteen means that in a hundred such tests, about ninety-nine did not record an airbag lamp fault. Nothing here says your car, or any model, will fail. The data records what testers found; it does not say why, and the causes include age, use, damp and whether a fault was fixed when the lamp first came on. A lamp that is out does not prove the system works, and an MOT pass is not a safety guarantee; it is a check on the day.
Frequently asked questions
Yes. If the airbag or Supplementary Restraint System lamp shows a fault, the manual classes it as a Major defect and the car fails. It failed about 1 in 85 first tests on cars aged 15 and over in 2021 to 2025, and about 1 in 800 on cars aged 3 to 5. A lamp that only shows the passenger airbag is switched off is not a defect.
Every statutory belt is checked for condition, buckle, retractor and the strength of the metal within 30 centimetres of each mounting. A missing belt, a weakened webbing, a buckle that does not work or a retractor that does not pull the belt back are each Major defects.
Two items account for the rise. The airbag lamp is an electrical fault that becomes more common with time, from 0.1% of tests at age 3 to 5 to 1.2% at 15 and over. Corrosion near the belt mountings barely registers under ten years and reaches 0.9% of tests on cars over fifteen.
Seat belts and seats are on the GOV.UK list of items that can be retested free if the car goes back to the same test centre before the end of the next working day. Take it away for longer and a partial retest fee may apply.
Sources and method
Item shares are the number of class 4 first tests in each age band (test year minus first-used year) that recorded the item as a fail, divided by all first tests in the band, pooled over 2021 to 2025: 33,793,352 tests aged 3 to 5, 50,103,915 aged 6 to 9, 44,980,002 aged 10 to 14 and 31,405,150 aged 15 and over. The anchorage structure item was recorded on 268,897 tests aged 15 and over. Cohort shares are failed first tests involving at least one seat belt or restraint item divided by all first tests for cars of that first-used year, across models with 500 or more tests. A test can record several items, so rows do not add up. The MOT manual places the airbag (SRS) warning lamp in the seat belt and restraint family, so it is counted here.
- DVSA anonymised MOT results, class 4 first tests, 2021-2025
- GOV.UK: MOT inspection manual, section 7 (seat belts and supplementary restraint systems)
- GOV.UK: Seat belts: the law
- GOV.UK: Child car seats: the rules
- GOV.UK: MOT retests
- GOV.UK: Check the MOT history of a vehicle
About these figures. Figures are computed by SortedCars from the DVSA anonymised MOT results dataset (class 4, first tests only, test years 2021-2025), published under the Open Government Licence v3.0. Pass rate = passes divided by first tests, with pass-after-rectification counted as a fail. No figure is shown for any group with fewer than 500 tests. Test class 4 only, first tests only; retests are excluded. Pass rates describe fleets, not individual machines: they reflect how cars were driven, maintained and used as well as how they were built, and beyond recorded mileage none of that is in the data. A well-kept example of a model with a weak average can still pass; a neglected example of a strong one can still fail. Alias spellings of a make are counted under one make name and all trims of a model under one model name, using SortedCars' grouping tables.
This article is general information drawn from published test records. It is not professional, mechanical or legal advice, and an MOT pass or a clean MOT history does not guarantee that a car is roadworthy today. If you are unsure about a car, have it inspected by a qualified mechanic. You can check any vehicle's MOT history free on the official GOV.UK MOT history service.
Check a car's MOT history free
Enter a registration to see its DVLA record and full MOT history, free, no sign-in.