MOT Lighting Failure Cost: £5-80 to Fix (12.75% of UK Fails)

Lighting tops the DVSA failure table for one structural reason: it is the easiest thing to catch and the easiest thing to neglect. A bulb burns out silently. Most drivers do not walk around their car checking every light before they set off in the morning. The MOT is the moment that uncaught failure surfaces.

The flip side is that this is the cheapest failure category to prevent. Twenty minutes of preparation before the test can eliminate the most common lighting fails. A walkaround with the engine running and a friend pressing the brake pedal will catch nearly every issue this category covers.

For the broader picture of how lighting compares to other failure types, see our top 10 MOT failures overview.

This check, done the day before your test, catches roughly 90% of lighting failures and costs nothing.

1. Park on a flat surface, engine on, headlights on dipped beam. Stand 3 metres in front of the car. Both headlights should be visibly lit.
2. Switch to main beam. Both should brighten. If one stays dim, that filament has failed.
3. Walk around the car checking sidelights. Front and rear should be lit. Number plate light should be visible from behind.
4. Indicators. Activate left, then right. Check front, side repeaters and rear.
5. Brake lights. Get a friend to press the pedal, or back up to a wall and watch the reflection. All brake lights (including the high-level brake light) should illuminate.
6. Hazards. All four indicators should flash together at the same rate.
7. Fog lights. If your car has front or rear fog lights, switch them on individually. They are tested if fitted.
8. Reverse light. Engage reverse gear (engine on) and check the white light at the back illuminates.

Any bulb that fails gets a £3-15 replacement from Halfords, Euro Car Parts or any motor factor. Look up your car's bulb codes on the inside of the V5C or the bulb pack at the parts counter. If you do not have a multi-pack of common bulb sizes in the boot, buying one (£15-25) is a one-time investment that prevents this entire failure category for the next 5-10 years.

The cheap end of lighting repair (£3-30) covers almost every fail. Three scenarios push the bill higher.

LED brake light units on modern cars. Many cars built after 2018 use sealed LED brake light assemblies. A single failed LED segment usually means replacing the entire unit, not a single bulb. Genuine parts can run £80-180; aftermarket equivalents £40-100.

Headlight unit cracks or water ingress. A cracked headlight lens or condensation inside the unit can fail the test if it affects the beam pattern. Full headlight assemblies are typically £60-400 depending on the vehicle.

Wiring or switch faults. If a light circuit is failing rather than a bulb, the diagnostic and repair can take 1-2 hours of skilled labour. Expect £60-150 plus any parts.

None of these is common. The vast majority of lighting fails resolve with a single £5 bulb and a screwdriver. If you have been quoted significantly more, ask for the specific defect code from the MOT report (lighting items begin with code 4) and consider a second opinion. The fail process page covers your rights.

Even working bulbs can fail the test if the beam aim is out of specification. Headlight aim drift happens for several mundane reasons.

• Loaded boot before the test (extra weight tilts the rear down, raising headlight aim).
• Worn rear suspension or coil springs.
• Uneven tyre pressures.
• Recent suspension or steering work that disturbed the aim adjustment.
• Dashboard aim adjuster set to the wrong position (most modern cars have a 0 / 1 / 2 / 3 dial for load compensation).

A garage with a beam-aim tester can adjust most cars in 15-20 minutes for £10-30. Some MOT testing stations include this in the test if it is borderline. Before the test, check the dashboard headlight-level dial is set to 0 (driver only, no load).