MOT defect file
Seat belt damaged or not working properly
Last updated
Quick answer
A belt is cut, frayed, stretched, or its buckle or retractor no longer works as it should. Every seat belt fitted to the car is tested, not just the front pair, and there is no advisory grading for one that has failed.
- Typical cost
- £60–£300
- DIY viability
- Possible with care
What you might notice
- The belt creeps back slowly, stops halfway, or has to be helped by hand to wind in
- Fraying or fluffing along one edge of the webbing, usually where it rubs the pillar guide or the buckle tongue
- A buckle that will not click home first time, releases under load, or needs a hard push to let go
- A belt that no longer locks when you tug it sharply — worth testing yourself, since it is the check the tester will do
What causes it
- Everyday abrasion against the pillar guide, the seat frame or a door shut, which cuts the edge of the webbing where it matters most
- Grit, coins and dropped debris in the retractor mechanism, which is why rear belts on family cars often stop retracting first
- A previous collision that stretched the webbing or deployed the pre-tensioner, leaving a belt that looks serviceable but is not
- Sun damage and repeated wetting on a convertible or a car parked outside, which stiffens the webbing and jams the reel
Advisory or failure?
There is no advisory or minor version of this — every seat belt defect in the fitment and condition check is graded major. A statutory belt missing, webbing or a flexible stalk significantly stretched, damaged or weakened, a belt not functioning as intended or of the wrong type, a buckle missing, damaged or not working as intended, and a retractor not working as intended are all major defects. The tester works to measurements on the webbing: cuts or damage over 2mm at the edges of the belt, where tensile strength matters most, and over 4mm away from the edges. Any cut at all on a child seat belt is a defect. Every belt fitted is examined, including belts on child seats permanently attached to the car, and folded seats are lifted to inspect the belts underneath. Two things are not defects: superficial fluffing that does not reduce strength, and a belt with no corresponding seat, which is not inspected. Where a child seat blocks access to a buckle, the tester checks what they can reach and issues an advisory that the buckle could not be seen.
Can you fix it yourself?
Possible with care
Freeing a lazy retractor is often just cleaning: with the belt fully out and the reel exposed, clearing grit from the mechanism and the pillar guide fixes a surprising number of them. Replacing an assembly is two or three bolts, but the bolts are the point — they are a specific high-tensile grade with a shouldered head, they take a torque figure, and you must reuse the original bolt and spacers rather than a bolt out of the tub. Never wash webbing in detergent or bleach, which weakens the fibres, and never knot, shorten or sew a belt. If the car has pre-tensioners, disconnect the battery and leave it for the manufacturer's stated time before touching a belt at the reel, because these are pyrotechnic devices. Buy a matching part: a belt of the wrong type or length fails on that alone.
What it costs
A complete front belt assembly is £30 to £90 for a good used part from a breaker, or £120 to £350 new from a franchised dealer, with about half an hour to an hour of labour to fit — most of which is removing and refitting the trim panel that hides the reel. That puts a straightforward front belt swap at £60 to £180 all in. The top of the band is a belt with an integrated pre-tensioner, which is priced as an original part and generally not sold used for good reason, plus a fault code to clear afterwards. Rear belts are usually cheaper in parts but can need the seat base and side trim out, so the labour evens things up.
What happens if you ignore it
A belt with a cut edge or stretched webbing may hold for normal driving and tear at the load it exists to carry, and a retractor that does not pull the slack in leaves you with the belt sitting away from your hip — which is where submarining under the lap belt starts. Not wearing a belt is a fixed penalty of £100 and up to £500 on conviction, and a belt that does not work leaves you in exactly that position through no choice of your own. It is also among the cheapest failures on the list to put right, which makes it a particularly poor reason to pay for a retest.
Common questions
- Is a frayed seat belt an MOT failure?
- It depends how bad it is. Every seat belt defect in this part of the test is graded major, with no advisory version, so webbing that is significantly stretched, cut or weakened is a failure. Superficial fluffing that does not reduce the strength of the belt is not a defect at all, so a slightly furry belt can still pass.
- How much damage is allowed on a seat belt before it fails?
- The tester works to measurements: cuts or damage over 2mm at the edges of the webbing, where tensile strength matters most, and over 4mm away from the edges. On a seat belt fitted to a child seat, any cut at all is a defect. Damage at the edge is treated more harshly because that is where the load is carried.
- Are rear seat belts checked during an MOT?
- Yes. Every belt fitted to the car is examined, not just the front pair, including belts on child seats permanently attached to the vehicle, and folded rear seats are lifted so the belts underneath can be inspected. A belt with no corresponding seat is not inspected. Where a child seat blocks a buckle, the tester issues an advisory saying it could not be seen.
- Can I fix a seat belt that will not retract?
- Often yes, because a lazy reel is frequently grit rather than a failed mechanism, and cleaning the retractor and the pillar guide with the belt pulled fully out cures a surprising number of them. A retractor not working as intended is a major defect, so it does have to be right. Never wash webbing in detergent or bleach, and never knot, shorten or sew a belt.
- How much does it cost to replace a seat belt?
- A complete front belt assembly is £30 to £90 for a good used part, or £120 to £350 new from a franchised dealer, with half an hour to an hour of labour, so a straightforward swap is £60 to £180 fitted. A belt with an integrated pre-tensioner is the expensive case. Fit the matching part, because a belt of the wrong type fails on that alone.
Cars this happens to most
Of every model with at least 2,000 tests in the DVSA data, these record seat belt damaged or not working properly on the largest share of their MOTs. Across all of them the typical rate is 0.4% of tests.
128 times in 2,780 tests
- Renault Modus2.6%
269 times in 10,194 tests
- Mazda CX-31.9%
484 times in 25,300 tests
- Volkswagen Taigo1.1%
64 times in 6,095 tests
27 times in 3,253 tests
- Citroen Berlingo0.8%
1,406 times in 179,716 tests
- Ford S-Max0.7%
477 times in 67,947 tests
- Toyota RAV-40.7%
177 times in 26,977 tests
A high rate here is a property of the fleet as much as the car: these models skew old, and almost everything fails more with age. It is a reason to check the item on a used example, not proof the model is badly built. Models with fewer than 2,000 tests are left out because a rate drawn from a few hundred cars moves too much to rank.
Warning lights behind this
This defect is what a tester writes down. What you see from the driver’s seat is a symbol, and it is worth checking which one, because manufacturers reuse the same shape for more than one system.
Fault codes behind this failure
A failure certificate records that the lamp was lit, not what lit it. If this is what your certificate says, one of these codes is usually stored behind it, and reading it is the difference between a diagnosis and a guess.
This is general guidance, not a diagnosis. The severity DVSA records depends on the specific fault found, so the same item can appear as an advisory on one test and a failure on another. Ask a qualified tester or mechanic to inspect the vehicle.
Has this been recorded on your car?
Check the full MOT history for any UK registration.