Xenon - high beam OK, low beam not working

TerminatorX5 · #1 02-04-2014, 10:08 PM

and you said that there was a moment when both lights, left and right were on?

going from simple to more complicated, I would troubleshoot the xenon light bulb - (some of them you already have completed)

pull the bulb from the "defective" location and put it into the operating location - if problem moved, problem is with the bulb, if problem remained on the drivers side,

i would pull the ballast from "defective" side and try it out in the operating side - if the problem moved, problem is with the ballast, if the problem remained, then

I would try to source BMW software, or get a mechanic who has BMW software, such as GT1 or INPA and read the status of the LCM

since there are NO fuses protecting the light bulbs, you might have one of the MOSFET transistors gone bad, which will call either for a new (used?) LCM or a repair to existing one... the LCM troubleshooting is more involved thus lets hope that the problem is with the light or the ballast...

E53inLA · #2 02-06-2014, 11:26 AM

First he installed brand new Flosser D2S bulbs. That didn't fix the problem.

Then we installed a "used but working" Hella ballast I bought from EBay on the drivers side. That didn't fix the problem. Then we swapped the ballasts, so the one originally on the pax side is now on the drivers side.

In order to isolate whether it was a problem within the headlight assembly, or something further upstream, we removed both assemblies and temporarily hooked them up on the wrong side. Then they both worked.

Then we hooked them back up on the correct side, but the retaining cages were removed, and we only had them held in place with one screw. They both worked.

Then we removed the headlight assemblies, reinstalled the retaining cages, and put it all back together with all the screws... and we are back to square one - Driver side low beam doesn't work.

Will try the software suggestion. Thanks & speedy recovery to you.

Is there any point trying to disconnect battery, wait, and reconnect? I see that often suggested in other threads.