Either the webbing itself is damaged — fraying, cuts, chemical damage — or the inertia reel isn't locking or retracting as it should. Both mean the belt won't restrain properly in an impact.
Wording as it commonly appears on an MOT certificate: “Seat belt webbing damaged or the retractor does not lock”.
What does it mean?
Either the webbing itself is damaged — fraying, cuts, chemical damage — or the inertia reel isn't locking or retracting as it should. Both mean the belt won't restrain properly in an impact.
How serious is it?
Usually recorded as: Major. The tester assesses the actual vehicle on the day, so your certificate is what counts.
What normally causes it?
- Wear and fraying where the belt runs over a plastic guide
- A retractor mechanism gummed up with dirt or damaged by water ingress
- A belt trapped in the door repeatedly
- Corrosion inside the B-pillar affecting the reel
What a mechanic would check
Pull the full length of each belt out through my hands looking and feeling for damage, give it a sharp tug to check it locks, and watch it retract fully on its own. Then check the anchorage bolts and the surrounding metal for corrosion.
What might need replacing
- A replacement seat belt assembly
- Anchorage repair if the surrounding metal is corroded
Can you still drive it?
It's a failure and it's not one to compromise on. A belt that doesn't lock offers very little in a crash. Get it replaced before the car is used to carry anyone in that seat.
Repair cost
Belt assemblies vary by car and whether it's a pretensioner unit. Second-hand belts are a false economy — you've no history on them and no way to know if they've been loaded in an accident.
Before the retest
Pull each belt all the way out and check the webbing for cuts, fraying and stitching damage, then give it a sharp tug to make sure it locks. Every buckle should latch and release cleanly. If an airbag or seat belt warning light is on, have the fault read and fixed before the retest; a lit warning lamp is a fail in its own right.
Retest rules
If the vehicle stays at the test centre for repair and is retested within 10 working days, a partial retest is often free; some items qualify for a free retest if you bring the car back by the end of the next working day. The exact conditions are set out on GOV.UK, so confirm with the test centre before you leave. A major or dangerous failure means the car cannot legally be driven away unless the previous MOT is still valid and nothing dangerous was recorded — check your certificate first.
Related help
More seat belts and restraints failures · MOT failure decoder · Ask a mechanic about your certificate
This is general guidance from a UK mechanic, not a substitute for a physical inspection. Only the tester who inspected your vehicle can confirm what was recorded and why.