Low Beam Xenon Stop Working? Workaround DIY + Diag Questions

[crystalworks]

This is workaround is for if your LCM has disabled one of your low beams due to inoperable ALC module under headlight. Or, if you have a bad LCM entirely that has disabled a headlight.

Well, thought I'd post up a quick workaround for one of the xenon low beams not working. From spending a bunch of time reading about this, I think this is caused by the ALC module under the headlight dying and the LCM disabling the headlight as a result. I can only guess that this would be to alert the owner there was a problem with the ALC, since let's face it, not everyone notices their headlights doing their dance at startup. There is a check coding you can disable in the LCM to have it allow the xenon to function even with the faulty ALC module... but I don't have DIS, INPA, or any of the other software packages figured out yet as far as getting them to run and connect to the truck so I had to do this method.

The nice thing about this is that it's all done inside the truck by the LCM and behind the glove box. Keeps it clean under the hood of aftermarket wiring. Plus, it's easy to remove from one location upon repair of the faulty component.

Step 1: Gaining Access
- Remove the passenger side side sill. Best to use panel poppers here or you will be replacing a few of them, or worse breaking the sliders that the clips go into on the back of the sill. I forget how many clips there are, around 6 maybe

- Remove the lower kick panel under the glove box. Pull out the bit of door weather stripping that helps hold it in place. It is held in with 2 pop clips similar to those on the door panel you messed with the last time you did your window regulator(s). These have a high likely hood of breaking.

- Remove the lower panel holding the courtesy light under the glove box. 1 scew and 2 plastic twist pins keep it in place. You can let it dangle, but easier to pop out the light and use it to help illuminate your work area.

- Remove the glove box. I know, I know, this sounds like a lot of removing stuff. It all takes about 10 minutes really once you've done it once. There are 4 screws on top and 1 on each side holding in the glove box. You will need to remove the pin from the shock to access the two on the side. Don't force it, if you haven't removed 6 screws, it won't come out. Once you have removed 6 screws give it a gentle pull forward and maybe a wiggle or two and it will come right out. Disconnect the glove box light and the flashlight/charging port light harnesses. Set it aside.

Step 2: Wiring
- I used a 4 pin relay because I had a nice handy harness clip to go with it but you could use the more common 5 pin as well. The wiring would be different, but uses the same principle. Close the coil using the power line from the low beam that works (right in my case) on the LCM and any ground. I used the ground terminal just under the LCM.

- The other 2 pins on a 4 pin relay will go to +12v (I used the fuse box behind the fuse box) and the other to the left headlight wire coming off the LCM. This sounds complicated I know... it's not.





- To access the fuses shown above, you could use any one of them to tie your +12v into btw, doesn't have to be the one I did, you remove 4 torx screws (t20 I believe).

- So now you have your +12v and your ground figured out. The other two wires are going to be located at the LCM that is held on by 2 8mm screws. It has 3 harnesses, we are concerned with the 2 outer ones. A 15 pin black (X12) and a 15 pin white (X38). The wires in question are the yellow/green (pin 11 on X12 for low beam xenon left side) and yellow/blue (pin 3 on X38 for low beam right side). You can tie into these really easily by just putting a tap on it, of like me cutting a slit into the harness and opening up an "eye" to put your new wire through and wrap around the wire. This helps make a mechanical connection and then I follow up with a bit of solder as well for good measure.

- If your right side is the functioning light (like mine), you want that wire to go to the other side of the coil (ground was the other) so that when you turn on your lights it trips the coil and makes contact with your +12v feed to your left non-functioning light. See below how I have my coil labeled. This makes it easy to at a glance see that I need my right low beam wire and my ground to go to those two terminals. The coil wires can be very small gauges as the relay's coil draws very little current. Your wire coming from +12v and going to your dead low beam wire you will want to be a higher gauge as they will carry the same load as the factory wires do. I matched the factory wire gauges with I think 16 gauge or 18 gauge, not sure? I also have the +12v line fused as shown with a fuse holder.



- If your left side light is the functioning light, you will do the reverse of the above. Your left side wire feed will go to the coil along with your ground and your right side wire will be the one that makes continuity with the +12v feed. I know it sounds complicated.

- Once all that is done you can plug your X38 and X12 back into the LCM to test functionality. If you are lucky both of your low beams should now illuminate whether the switch is in the Auto/Adaptive setting or just set to on. If you are like me, your leveling still does not work on the dead headlight. I have still not figured out why mine doesn't but I've narrowed it down to something at the headlight. Either the ALC or the stepper motors inside the headlight. Below is what it looks like finished with the relay tucked back up with the factory relays and modules.



Step 3: Cleanup
- Reinstall everything in the reverse order of removal (duh).

- Cleanup all your tools and enjoy having low beams again without risking damaging your LCM by asking it to power two headlights off one circuit. This may be acceptable... I have no idea, but my OCD wouldn't let me do it that way. If you were going to do it that way... a short 8" wire of acceptable gauge going from the yellow/green to the yellow/blue would be all you would need to accomplish this. But I digress.

I'll add wiring diagrams for 4 pin and 5 pin relays tomorrow. Getting late... If anyone has a guess as to why my ALC module under the headlight is not functioning by all means chime in. I tested the signal wires going into the headlight from the module behind the glove box and both were sending signals.

[crystalworks]

This solution has worked great for retaining headlight functionality despite non functioning ALC. I just recently got INPA and the other BMW software running and was able to reset the system so all is working now with the lighting system. Going to remove this workaround to clean everything up.

What had ultimately happened was water intrusion into the headlight that caused the failure of the ALC module under the left headlight. The LCM then disabled the low-beam. I replaced the ALC module with a used one but could never reset the system without BMW software on a laptop. I was able to verify all motors and functionality good with a Foxwell, though was not able to find a reset in its menus for the system.

Just thought I would post an update as low beam Xenon fault threads pop up from time to time and this is something to check after ballasts/bulbs have been eliminated as a cause.

[wpoll]

Great post(s), CW - tucking all this info. away, just in case.

[crystalworks]

Bumping this to post the ultimate solution to the headlight issue I was having.

It ended up being corrosion on the ALC module on my left (DS in the States) headlight. I ordered a used replacement off of Ebay, installed it and would still not get working ALC or low-beam. After months, I finally found that the ALC system had to be reset in INPA (ISTA could do it too I assume). After I reset the system I once again had working ALC (both leveling and directional movement). I was then able to remove my workaround wiring all together.

Hope this helps someone as I see non-func headlight posts come up every so often.

[Salty B.]

My left works, but is noticeably dimmer than the right even after replacing the bulb. Tried replacing the... ballast/igniter/silver box under the headlamp but the Chinese copy I bought off ebay didn't work at all so I put the old one back in. Related? Both low beams do the startup dance.

[wpoll]

Originally Posted by Salty B.

My left works, but is noticeably dimmer than the right even after replacing the bulb. Tried replacing the... ballast/igniter/silver box under the headlamp but the Chinese copy I bought off ebay didn't work at all so I put the old one back in. Related? Both low beams do the startup dance.

Bad lens/reflector on the left?

[crystalworks]

Originally Posted by Salty B.

My left works, but is noticeably dimmer than the right even after replacing the bulb. Tried replacing the... ballast/igniter/silver box under the headlamp but the Chinese copy I bought off ebay didn't work at all so I put the old one back in. Related? Both low beams do the startup dance.

If your ALC is working and the bulb ignites at all, no won't be related to this issue. Wayne's idea is better or you used an inferior bulb for the replacement. Try switching the bulbs. That will eliminate the bulb as the issue.

Then you can swap the ballasts to determine if it is a ballast issue. But typically when one of those fail, the bulb fails to ignite or blinks/pulses. In my experience anyway.

[Salty B.]

Originally Posted by wpoll

Bad lens/reflector on the left?

Unsure, but it was pristine inside when I got the old lens off after a huge fight.

Both bulbs were replaced at the same time, and I've swapped them. No change.

I'll try swapping the ballast next. I have a junkyard spare but no idea if it's any good.