The horn doesn't sound, is too weak, or makes a sound that isn't a continuous, uniform note. Two-tone air horns, sirens and musical horns are not acceptable on a road car and get recorded here too.
Wording as it commonly appears on an MOT certificate: “Horn not working or not suitable”.
What does it mean?
The horn doesn't sound, is too weak, or makes a sound that isn't a continuous, uniform note. Two-tone air horns, sirens and musical horns are not acceptable on a road car and get recorded here too.
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?
- A corroded horn unit — they live behind the bumper and get everything the road throws at them
- A blown fuse or a failed relay
- A broken clock spring behind the steering wheel, which usually kills the airbag light and steering wheel buttons at the same time
- A corroded earth at the horn bracket
What a mechanic would check
Press it and listen first, then work backwards: fuse, relay, feed at the horn, earth. If the airbag light is on as well I go straight to the clock spring, because that one fault explains both symptoms and there's no point buying a horn.
What might need replacing
- A horn unit
- A fuse or relay
- An earth repair
- A clock spring in the worst case
Can you still drive it?
Safe enough mechanically, but the horn is your only warning to a pedestrian stepping out. It's a Major fail so it has to be fixed before the retest either way.
Repair cost
A horn or a fuse is a cheap part. A clock spring is more involved because the steering wheel and airbag have to come off.
Before the retest
Battery, wiring and horn faults are usually quick to fix but easy to forget about. Make sure the battery is clamped down so it cannot move, the terminals are tight and there is no fluid leaking. Check that no wiring hangs loose or rubs on moving parts, and that the horn gives a steady, continuous note.
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 electrical 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.