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.
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.