E39 intermittent tail/head light fault

[jeffbebe 1559]

Every now and then in the last couple of days - and it seems to happening more frequently - I get a fault signal on the dash for the front right and rear right head and tail lights. While the fault signal is lit, the lights aren't going but sometimes I'll stop the car and the fault will disappear and the lights will work as normal, so it's obviously not the bulb but a wiring issue (or something like that).

Any ideas? I'm no sparky so tempted to take it to an auto electrician unless folks can recommend a very simple test/fix.

Cheers in advance.

[BM WORLD 1283]

a comon issue with e39 e38 etc is the LKM light control module failing.

mounted behind the right front kick panel.

have spares if needed

[jeffbebe 1559]

a comon issue with e39 e38 etc is the LKM light control module failing.

mounted behind the right front kick panel.

have spares if needed

Thanks Brent. How do I check if that's the issue? And how much does a replacement cost?

[hotwire 352]

As Brent said - LCM modules do fail.

That said - could well be a faulty bulb/connection in those circuits.

The reason for the failure coming up with lights not on is because the LCM "cold monitors" all the circuits it controls. This done by sending a quick pulse through each circuit every 30 sec or so to check for bulb failure.

Our E39 is currently showing a fault "front fog lamp failure" (typical auto sparky - not yet fixed my own car ) lights were going & I thought it was talking sh*t... or maybe a bad connection. The other night in the garage, as I started the car & flicked the lights on - noticed a delay of several seconds in the R/H fog light coming on. Oops maybe it isn't lying . No doubt a crook bulb - now to see how long it takes me to fix it - as I keep getting reminded by the other half.

[jeffbebe 1559]

The bulb's fine but I took another look today and noticed a bit of corrosion around the bayonet. Probably some moisture getting in there which isn't ideal. Cleaned it up and haven't had the fault light come on again but I'm guessing that's an issue that will persist unless I stop water getting in.

[hotwire 352]

Bear in mind a bulb can seem fine but still have a broken filament & operate intermittently, as it cools down it contracts breaks circuit & can fail on re igniting - vibration causing it to reconnect. I suspect this will be the case with my fog light bulb.

The corrosion around it will certainly also cause it to trip the failure. The LCM monitors the current flow very precisely.

[jeffbebe 1559]

Bear in mind a bulb can seem fine but still have a broken filament & operate intermittently, as it cools down it contracts breaks circuit & can fail on re igniting - vibration causing it to reconnect. I suspect this will be the case with my fog light bulb.

The corrosion around it will certainly also cause it to trip the failure. The LCM monitors the current flow very precisely.

Has been fine since I cleaned it up but will replace the bulb soon anyway as it looks like it's on its last legs.

I recently put a new M5 bumper on my E39 and foolishly forgot to check what connection type the fog bulbs have. I want to replace with some white bulbs to match the angel eyes and projectors - is there an easy way to check the fitment?