MOT defect file
Lamp not working
Last updated
Quick answer
A side, brake, indicator, fog or registration plate lamp failed to operate. Typically a bulb or a corroded holder.
- Typical cost
- £10–£80
- DIY viability
- Straightforward
What you might notice
- Indicators flashing at roughly double the usual rate, which is the standard sign of a failed bulb in that circuit
- A brake lamp out — almost always reported by somebody else, since you cannot see your own
- The number plate lamp quietly no longer working, easy to miss and a common reason to be pulled over at night
- Condensation inside a lens, or a lamp that works intermittently while the car is moving
What causes it
- A blown bulb, which is the answer most of the time
- Corrosion in the holder, particularly in rear clusters where the lamp gasket or boot seal has let water past
- A poor earth, which typically makes two circuits misbehave together — a tail lamp glowing when you indicate is the giveaway
- A failed relay or fuse, or on newer cars a fault in the body control module that drives the lighting
Advisory or failure?
A mandatory lamp that does not work is a major defect and a failure. That covers front and rear position lamps, stop lamps, indicators, hazards, the rear registration plate lamp, the rear fog lamp on vehicles first used from April 1980 and reversing lamps on vehicles first used from September 2009. The grading softens for lamps with several light sources: at least half still working makes it a minor defect, and only below half does it become a major. Colour counts as well — an indicator showing white where it should be amber, or a lens cracked so that white light shows to the rear, is a major defect whether or not the bulb lights.
Can you fix it yourself?
Straightforward
Most bulbs are reached from behind the cluster, often through a flap in the boot trim, and cost a couple of pounds. Have somebody watch while you work through every light, or reverse up to a window or garage door and use the reflection. The traps are small but real: LED replacement bulbs fitted to a car not designed for them can trigger a bulb-failure warning or hyper-flashing, and if they are not E-marked for road use they will fail the test regardless. If a new bulb blows straight away, stop and look for a chafed wire rather than fitting another.
What it costs
A bulb is £2 to £8 and takes minutes, so a self-fix costs almost nothing and a garage will usually charge £15 to £30 including the part. The top of the band is where the bulb was not the problem: a corroded rear cluster replaced with an aftermarket or used unit is £40 to £80, and chasing an earth or a wiring fault is charged as diagnostic labour, which is where the time and money actually go.
What happens if you ignore it
A defective lamp is a fixed penalty offence, and a dead brake lamp removes the only warning the driver behind gets that you are slowing — a straightforward way to be hit from behind and be found at fault. Bulbs are the cheapest items on the whole test, which makes a lighting failure a particularly poor way to fail: you pay for a retest over a part worth a couple of pounds.
Common questions
- Which lights are checked in an MOT?
- Front and rear position lamps, stop lamps, indicators, hazards, the rear registration plate lamp, the rear fog lamp on vehicles first used from April 1980, and reversing lamps on vehicles first used from September 2009. Any mandatory lamp that does not work is a major defect and a failure. Colour counts too, so an indicator showing white where it should be amber also fails.
- Will aftermarket LED bulbs fail an MOT?
- They can. An LED bulb fitted to a car not designed for one may trigger a bulb-failure warning or hyper-flashing, and if it is not E-marked for road use it will fail the test regardless of how brightly it works. Check the marking before you buy rather than after the test.
- Is a number plate light an MOT failure?
- Yes. The rear registration plate lamp is a mandatory lamp, so one that does not work is a major defect and a failure. It is also easy to miss from the driver's seat and a common reason to be pulled over at night, despite the bulb itself usually costing a couple of pounds.
- Why have two of my lights stopped working at once?
- That pattern normally points at a poor earth rather than two coincidental bulb failures. A tail lamp glowing faintly when you indicate is the classic giveaway, because the current is finding its way back through another circuit. A failed relay or fuse, or a body control module fault on a newer car, can also take out more than one lamp.
- How much does it cost to fix a lamp that is not working?
- A bulb is £2 to £8 and takes minutes, so doing it yourself costs almost nothing, and a garage will usually charge £15 to £30 including the part. A corroded rear cluster replaced with an aftermarket or used unit is £40 to £80. Chasing an earth or a wiring fault is charged as diagnostic labour, which is where the money actually goes.
Cars this happens to most
Of every model with at least 2,000 tests in the DVSA data, these record lamp not working on the largest share of their MOTs. Across all of them the typical rate is 3.0% of tests.
- Isuzu Rodeo16%
689 times in 4,178 tests
2,875 times in 18,445 tests
742 times in 4,826 tests
- Nissan NV20015%
3,751 times in 24,703 tests
362 times in 2,620 tests
466 times in 3,438 tests
1,103 times in 8,383 tests
- Peugeot 30713%
2,799 times in 21,622 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.
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.