HID low/high beam out but bulb and ballast both work fine...

[Sneux]

Hey guys, I have a few questions regarding the HID headlights on my 2008 Z4!

My low/high beam HID is no longer functioning but when I switch the bulb and ballast to the other side they light up just fine. This leads me to believe it may be the assembly as it had quite a bit of moisture in it recently... Is it worth looking at any other connectors before replacing the entire assembly?

If I do have to replace the entire assembly I definitely plan to do it myself but am confused as to the removal of the front bumper. I've read where there are supposed to be 7 screws underneath holding the bumper fascia to the front but I can't seem to any more than 2 of them on the ends near the wheel wells... Was this changed on the facelifted model?

 

[Bumpy]

No need to remove the bumper

https://www.youtube.com/watch?v=Ooh16mEY3hQ

This guy used a halogen bulb by mistake but the procedure is the same.
If you need more room, you can remove the front wheels.

Diagnostics:
There are 3 parts to the assembly.
The Bulb (they usually go pinkish before they let go.)
The Igniter (It attaches to the base of the bulb and has a very small connector that needs to be plugged in.
The Ballast .. I've never had to replace that. No idea how to trouble shoot that.
You did well to swap bits from side to side to try and identify the defect.

Hope this gets you started

 

[Sneux]

Thank you, that's actually the video I used to swap the parts around. My worry is that the entire assembly will need to be replaced since it seems the bulb and ballast are okay. In order to remove the assembly I've seen that I need to remove the front bumper fascia to reach the four screws attaching the assembly.

My confusion comes in at the fact that I have yet to see a guide that shows bumper removal with a facelift model. All of the older guides say to remove the seven screws underneath the bumper but I think that they may have changed how many are there after the facelift.

 

[MACK]

I think your ballast is probably knackered. It's not the two bits you've so far swapped. It's under the headlight and you need the bumper off and headlight to access it easily. The two bits you've changed so far are the bulb and the ignitor.
Bearing in mind you say you've had moisture issues is seems increasingly likely as they fill with water that's drains into them from the headlight itself. Sometimes you can dry it out and save it, but often it will need replacing.
The good news is that they aren't specific to the z4 or even bmw so there's usually used ones on ebay etc at reasonable cost. Be careful though as they're also a lot of dodgy fakes or badly repaired ones.

 

[Ducklakeview]

Thank you, that's actually the video I used to swap the parts around. My worry is that the entire assembly will need to be replaced since it seems the bulb and ballast are okay. In order to remove the assembly I've seen that I need to remove the front bumper fascia to reach the four screws attaching the assembly.

My confusion comes in at the fact that I have yet to see a guide that shows bumper removal with a facelift model. All of the older guides say to remove the seven screws underneath the bumper but I think that they may have changed how many are there after the facelift.

If you've followed that video, you've only swapped the actual bulb and igniter, the ballast is screwed to the underside of the headlight and as such you need it out to remove it. If you've had water in the headlight, it WILL have found itself into the ballast, as the connector between the two doesn't prevent water ingress from the headlamp housing to the ballast, and stupidly it's probably the only OEM ballast I've seen that isn't "potted" however, I have successfully dried out several that have then worked perfectly, so it may not be beyond recovering.

Mike