Bulb failure message, bulb still lighting
 

Hello All,

I’ve just got a Bulb Failure - Dipped Beam message.

So far, so normal.

The odd thing is, the bulb is not blown. It lights when the ignition is on and then, about a second after starting the engine, goes out and the warning message appears.

I suspect the bulb filament has broken and re-welded itself as the light is slightly brighter than the good side.

Does anyone know whether the bulb failure circuit will fail a lamp for being over current, as well as under?

If so, I’ll just change the bulb but if not, I suppose I’m looking at replacing the failure detection circuit.

Many thanks in advance for any thoughts on this...

Boots.

Swap the bulb out and test, that will give you your answer....

Yeah, I will but it’s the nearside one and changing that one usually means a lot of swearing and a visit to A & E afterwards to repair my wrist!

The bulb failure warning is a current measurement. When the correct current is measured the warning goes out.
I’m guessing at a thermal issue, as the bulb heats up the earth is lost. Start with the bulb, but anywhere in series will get hot if the conductivity is wrong.

No, it’s not a loss of continuity. The bulb stays on with constant brightness for as long as you like with the key at ignition only.

It only goes out after the engine is started and the ‘failure’ warning comes up.

So the bulb goes out?
If the bulb lights then the bulb is good. If it goes out then it’s the feed to it if subsequently the bulb works again.
With the ignition on, the voltage is around 12.5V. With the engine running it’s around 14.8V. The difference might be enough to force a heat related failure?

Hmm, maybe.

I will change the bulb tomorrow and see what happens.

Thanks for your input!

Removing the air filter box makes it a lot easier to get at the N/S headlamp bulb.