MOT defect file
Headlamp not working
Last updated
Quick answer
A headlamp did not illuminate on test. Usually a bulb, but can be wiring, a connector or a failed control module.
- Typical cost
- £20–£120
- DIY viability
- Possible with care
What you might notice
- One side of the road ahead noticeably darker than the other after dark
- Dipped beam working while main beam does not, or the reverse, on a car with a twin-filament bulb
- Flickering, or a lamp that cuts out over bumps and comes back on a smooth surface
- A bulb warning on the dashboard — though plenty of cars monitor exterior lamps loosely, and some not at all
What causes it
- A blown filament, which is simply the end of a halogen bulb's life at around two to five years
- A corroded holder or connector, common once the rear seal on the headlamp has perished and let water in
- A failed HID ballast or igniter on a xenon system, or a failed driver module on an LED unit
- Chafed wiring between the headlamp and the fusebox, or a blown fuse that is really pointing at a short elsewhere
Advisory or failure?
There is no advisory grading for a headlamp that does not light: a mandatory lamp failing to operate is a major defect and an automatic failure, and that applies to one dipped beam as much as to both. Where the headlamp uses multiple light sources, as LED units do, the grading splits — at least half still working is a minor defect, fewer than half working is a major. A lens discoloured, clouded or damaged badly enough to materially reduce light output is a major defect in its own right, and a headlamp levelling device that no longer functions is treated the same way.
Can you fix it yourself?
Possible with care
On an older car with a halogen bulb this is a ten-minute job and a £10 part, and it is worth changing both sides together because the second bulb will not be far behind. Handle the glass with a cloth, since skin oil creates a hot spot that shortens bulb life. Access is the real variable: on many modern cars the only route to the bulb is through a wheel arch liner, or with the battery or front bumper removed, which turns a trivial job into an hour. Xenon systems carry a high-voltage igniter and are best left alone, and sealed LED headlamps are generally not serviceable at all.
What it costs
A halogen bulb is £8 to £20 with nominal labour where access is good, so many of these are settled for under £30. Poor access adds an hour of labour, and a xenon bulb at £40 to £90, or a ballast at £100 or more, sits at the top of the band. Complete LED headlamp assemblies fall outside it altogether, since the unit is replaced whole rather than repaired.
What happens if you ignore it
Driving with a headlamp out is an offence and attracts a fixed penalty, and it halves what you can see on an unlit road while making the car harder for others to place — a single lit lamp reads like a motorcycle at a distance. Water that got in far enough to corrode one holder is still in there, working on the reflector coating and the rest of the connector, so the cost only goes one way.
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.