Is a Rear Fog Light an MOT Failure? Front and Rear Explained

Fog lights cause more MOT confusion than almost any other lamp, mostly because people assume the front ones do not count. The wording you are most likely to see on the certificate is this one:

Rear fog lamp inoperative (4.5.1 (a))

The Short Answer

A rear fog light that does not work will fail the MOT on most cars: vehicles first used on or after 1 April 1980 must have a working rear fog lamp on the offside or in the centre, and an inoperative one is a Major defect. Front fog lights are only part of the test on cars first used on or after 1 March 2018: on those, a wired-up front fog that does not work is also a Major defect. On older cars the front fogs are not inspected at all.

The rear fog lamp is the one that stops you being run into from behind in real fog, which is why every car from 1980 onwards must have one. Front fogs are optional equipment, and only cars first used from March 2018 have them checked.

What’s Actually Checked on the Rear Fog

The tester confirms the lamp lights, shows a steady red, is secure, and that the tell-tale on the dashboard works, so you know when it is on. A rear fog lamp that will not switch off matters too: dazzling following drivers in clear weather is its own hazard, and using it outside poor visibility is an offence worth knowing about.

What Usually Causes a Dead Rear Fog Light

• The bulb, as ever, first and cheapest.
• A corroded holder or earth in the rear cluster, the classic cause of a lamp that flickers with vibration.
• The switch or its relay: fog lamp circuits pass through a latching switch that has to remember its state, and they do fail.
• Wiring faults, particularly where towbar electrics have been spliced into the rear loom.

A Note on the Rest of Your Lights

Lighting is the single biggest failure category in the national MOT statistics, and nearly all of it is preventable with a walk-round the week before the test: headlamps, position lamps, indicators, number plate lamps, stop lamps and the rear fog. We covered whether a reversing light fails the MOT earlier this month, and what’s checked in an MOT runs through the full list.

Fixed While You Wait

Any of our 12 branches across Nottinghamshire will check every exterior lamp and replace bulbs while you wait. If the fault is in the switch, relay or wiring we will diagnose it properly and confirm the price before any work starts. Failed on a fog lamp? Same-day fix and retest is the normal outcome. Book an MOT online today.

Caught on inspection at our Stapleford branch: one front fog lamp lit, its twin dead. On a car first used before March 2018 the front fogs are not tested; on a newer car, or on the rear, a dead fog lamp is a fail.

Frequently asked questions

Will my car fail its MOT if the rear fog light doesn’t work?

Yes, on vehicles first used on or after 1 April 1980: the mandatory rear fog lamp must work, and an inoperative one is a Major defect under 4.5.1. The dashboard tell-tale has to work as well.

Are front fog lights part of the MOT?

Only on cars first used on or after 1 March 2018. On those, a wired-up front fog lamp that does not work is a Major defect under 4.5.1, the same as the rear. On older cars the front fogs are not inspected, and front fogs that were never connected and have no switch are not required to work on any car.

My car has two rear fog lights: do both need to work?

No. The MOT only inspects the one mandatory rear fog lamp, which must be in the centre or on the offside (the driver’s side). If that one works, a dead second lamp on the nearside will not fail the test, though it is still worth fixing.

When should I actually use the rear fog light?

Only when visibility drops below about 100 metres: seriously heavy fog, spray or snow. Using it in ordinary rain or clear darkness dazzles the driver behind and masks your brake lights, and it is an offence to use fog lamps when visibility is not reduced.

How much does it cost to fix a rear fog lamp fault?

It depends on the underlying cause and the vehicle, which is why we always inspect first. Once we can see exactly what is needed we will explain it in plain English and confirm the price with you before any work starts.