Your car clinic expert
Dave Pollard has written several Haynes manuals and has tested just about every car-related accessory.
Q. Three of the LEDs in my Volkswagen Passat’s rear-light clusters do not light up. The remaining 17 work fine. I thought these bulbs were supposed to last the lifetime of the car. Can I replace them, and would a failure to do so result in the car not passing its MoT?
MT, Crawley, West Sussex
A. Light-emitting diodes — better known as LEDs — are more robust and longer-lasting than conventional bulbs but no manufacturer guarantees them for the lifetime of a vehicle. The biggest LED-killer — and indeed for any in-car electronics — is moisture. Rain could be getting into the cluster through a damaged seal; keeping the water out should ensure that the problem does not recur.
Remove the cluster and check that the seal is in good condition and not kinked in any way. A light smear of a clear sealant (for example, Granville Silicone Sealant, £4.99 at halfords.com) on both sides of the seal will keep it watertight and flexible. A spray of WD-40 around the electrical connections will also help keep moisture at bay.
The Road Vehicles Lighting Regulations 1989 require that the rear lights are in “good working order” and kept lit between sunset and sunrise or in times of seriously reduced visibility.
What constitutes good working order is open to interpretation but in respect of the MoT the advice from the Department for Transport is that at least 50% of the LEDs must work. So at present your light clusters would meet the MoT standard.
If you still want new bulbs, individual replacement is not possible on your car. Complete clusters are available on various websites, including eBay, from £60 upwards, depending on the exact model. DP