MOT defect file
Seat belt anchorage corroded or weakened
Last updated
Quick answer
The metal the seat belt bolts into has rusted or been weakened within the 30cm prescribed area around the anchorage. It has to be cut out and welded to original strength — filler and plated patches are not accepted.
- Typical cost
- £250–£800
- DIY viability
- Garage job
What you might notice
- Nothing you can see or feel — this is found from underneath, with the tester pressing the metal around the mounting with finger and thumb
- Blistered paint or flaking rust low down on the B-pillar, along the inner sill or in the boot floor near a rear belt mount
- A belt mounting that visibly moves in its panel when the belt is pulled hard
- Damp or musty carpet in a footwell or under the boot mat, which usually means the floor beneath has been rotting from the inside
What causes it
- Road salt collecting inside the sill or the rear wheel arch, where drain holes have silted up and water sits against bare metal
- A water leak from a perished door seal, a blocked sunroof drain or a screen bond, soaking the carpet and rotting the floor pan from above
- An earlier repair done with filler, glass fibre or a pop-riveted plate over rust that was never cut out
- Stone damage and kerb scrapes on the outer sill breaking the paint film and letting corrosion get behind it
Advisory or failure?
The prescribed area is all load-bearing structure or supporting panelling within 30cm of the anchorage, measured in any direction — and it includes the seat mounting points where a belt attaches to the seat frame. Where the strength or continuity of that structure is significantly reduced, or has been inadequately repaired, it is a major defect. Where the anchorage is judged likely to become detached in a collision, the grading is dangerous. An anchorage that is simply loose in sound metal is a major defect. The tester decides by pressing with finger and thumb, or with a corrosion assessment tool, and must reject the area if it is holed, does not feel firm, or gives way under that pressure. Slight surface rust that does not reduce strength is not a defect at all, though many testers will note it as an advisory. The repair standard is the part people get wrong: within a prescribed area it must be continuously seam welded and at least as strong as the original, so filler, glass fibre, riveted plates and a coat of underseal over the top will all be rejected at the retest.
Can you fix it yourself?
Garage job
This is structural welding on thin, often rotten steel, and it is holding the one component designed to stop you leaving the car in a crash. It needs a MIG welder, the judgement to keep cutting back until sound metal appears, and the discipline to fabricate a proper repair section rather than plate over the hole. It also has to be done clear of fuel lines, brake pipes and the tank, with the interior trim, carpet and often the seat out of the way first. The useful DIY contribution is prevention: clear the sill and door drain holes each autumn, fix water leaks promptly and wash salt off the underside through winter.
What it costs
Almost all of this is labour, since the steel itself costs very little. A single localised repair — one belt mounting and the panel around it — is typically £250 to £450 at an independent welder, assuming reasonable access. The figure climbs with what has to come out first: seats, carpet, trim and sometimes the fuel tank or exhaust, all of which is time. Both sills, or a rear anchorage in a rotten boot floor, reaches the top of the band and can pass it. Get the car assessed and quoted before committing, because the rot found once cutting starts is usually greater than the rot that was visible, and on a car worth around £1,500 the honest answer is sometimes not to start.
What happens if you ignore it
The point of an anchorage is to take a very large load, once, at the worst moment of the car's life. Corroded metal around the mounting is what tears out when that load arrives, and the belt then does almost nothing. Nobody sees that coming from the driver's seat. The financial argument runs the same way as the safety one: rust works outwards from inside the box section, so the repair you decline this year is a bigger one next year, and there is a point at which welding costs more than the car is worth — which is how most older cars in Britain finally come off the road.
Common questions
- Is a corroded seat belt anchorage an MOT failure?
- Yes. Where corrosion has significantly reduced the strength or continuity of the structure within 30cm of the anchorage, or the area has been inadequately repaired, it is a major defect and a failure. If the tester judges the anchorage likely to become detached in a collision, the grading is dangerous instead. Light surface rust that does not reduce strength is not a defect.
- What is the prescribed area around a seat belt anchorage?
- It is all load-bearing structure or supporting panelling within 30cm of the anchorage, measured in any direction, and it includes the seat mounting points where a belt attaches to the seat frame. That is why rust in a sill, the base of a B-pillar, or a boot floor near a rear belt mount can fail the test.
- Can a corroded seat belt mounting be repaired with filler or a plate?
- No. Inside a prescribed area the repair must be continuously seam welded and at least as strong as the original panel, so filler, glass fibre, riveted plates and a coat of underseal over the top will all be rejected at the retest. The rot has to be cut out and new steel let in.
- How does an MOT tester check a seat belt anchorage?
- From underneath, by pressing the metal around the mounting with finger and thumb or with a corrosion assessment tool. The area must be rejected if it is holed, does not feel firm, or gives way under that pressure. None of this is visible from the driver's seat, which is why most owners first hear of it at the test.
- How much does it cost to weld a seat belt anchorage?
- A single localised repair is typically £250 to £450 at an independent welder where access is reasonable. Both sills, or a rear anchorage in a rotten boot floor, reaches £800 and can pass it, because almost all of the cost is labour: seats, carpet, trim and sometimes the fuel tank have to come out first. Have it assessed and quoted before committing.
Cars this happens to most
Of every model with at least 2,000 tests in the DVSA data, these record seat belt anchorage corroded or weakened on the largest share of their MOTs. Across all of them the typical rate is 0.8% of tests.
- Citroen Xsara8.5%
1,651 times in 19,396 tests
- Nissan Figaro5.0%
116 times in 2,319 tests
- Jaguar X-Type4.9%
946 times in 19,214 tests
- Daihatsu Terios3.8%
133 times in 3,513 tests
- Citroen 2CV3.6%
90 times in 2,466 tests
- Talbot Express3.6%
172 times in 4,826 tests
- Suzuki Jimny3.5%
814 times in 23,408 tests
- Mazda Bongo3.2%
281 times in 8,769 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.
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?
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