Headlight or LCM Issue?
 

My son's 2001 X5 has something wrong with the passenger side low-beam. The cluster displays the lamp warning and I've changed the bulb without out effect. I can swap the bulbs left to right and both work on the driver's side.

I've used a test light to check both sides. On the drivers side, I back probed the plug and the yellow wire carries voltage and the brown appears to be a ground. On the passenger side both the yellow and the brown seem to carry voltage.

Is this a sign of a bad LCM, is there a relay somewhere or do I have to keep digging for a short?

that is very odd. Do you have a Foxwell scanner? Your going to have to do some digging on this one. The Foxwell will allow you to operate each light independently. I would get a wiring diagram and see if you can trace it back and start a process of elimination. You can try another LCM. You will get the "tamper dot" on your odometer, but everything will work properly. If that isn't your problem, you plug your original back in and the tamper dot will go away. Welcome to BMW wiring hell!

Are you reading voltage on both wires going to the bulb with the lights turned on and the bulb in place and is this reading in reference to ground ?? (neg test lead to vehicle ground)

The brown wire is connected to chassis ground point (X166) so obviously there should be no voltage measured against ground.

https://www.pss-autosoft.net/diagram...s/G_120249.png

Yes. Bulb won't light and test light turns on both the ground and the power.

I have a set of aftermarket headlight assemblies installed. They came with a harness between the bulb and the OEM harness - basically just a plug with 2 wires and a bulb holder. I cut the ground on this harness and used a test lead to bypass the OEM harness to ground. The low beam works with this alternate ground.

I do have a Foxwell NT530. I pulled the codes and the LCM has a 28 - LCM Light Control Module fault stored. I haven't tried to use the scanner to do anything else beyond pulling the codes so far.

Then you have a problem either with the connector or the ground that Clavurion is pointing out.

Is it common for the connector on the vehicle harness to go bad? The car's not here at the moment, but I'll take a close look when my son get's back from school. Maybe I can de-pin the connector and test again.

It would be against all odds that a ground wire would damage and short to damaged voltage wire (without blowing a fuse). Sounds more likely that there is something wrong with that after market adapter.

If the ground side of the lamp circuit is lifted (not connected to ground) then both the +ve line and the ground line will read a voltage - with no current through the lamp circuit, there is no voltage drop across the lamp, so the lifted ground line will read a similar voltage to the supply line.

Do you mean measuring with the bulb still connected to the plug? If a voltage is measured it's measured against a clear ground point so there can't be any voltage on a broken ground wire which is not connected at each end.

This a problem (clearly not meaning you) when people are saying they are measuring something and they don't understand the basics what they are measuring. (And also no pun intended. We are all doing the best we can.)