2004 XC70 bi-xenon headlight high and low beam failure

[enotslim]

2004 XC70 with Bi-Xenon headlamps. Left/driver side high and low beams are both out. Is there any single issue that can cause this? Looks like high beam is bi-xenon, low beam is not bi-xenon and they use different fuses.

It is possible they are unrelated - that the high beam was out and I didn't notice because I almost never use high beams. And then the low beam went out, which I definitely did notice. I did have a lamp failure message but thought this was due to a known damaged side light. Maybe I misinterpreted the warning.

I'm looking for as much information as possible ahead of a repair since it appears that changing the bulb is more involved than I am accustomed to - requires loosening the bumper, etc. doesn't look difficult but also much more involved than simply removing the rear cover of the lamp housing and slipping in a new bulb.

And if the bi-xenon bulb is bad it sounds like replacing both sides is wise. Should the ballast also be replaced at ~140,000 miles or is it likely OK?

Thanks.

[enotslim]

Well, that wasn't bad at all. Bumper off and bulbs tested. Awaiting replacement bi-xenons and halogen high beams from fcp. There's just one thing. I think I mulched (along with my leaves) one of the black plastic pieces that hide the bolts that connect the bumper to its retainer. See photo.

Anyone know where to find one of these? FCP doesn't seem to cary and searching on line has been unsuccessful so far. I can make up something but would prefer the real thing front and off-center like this.

Thanks.

[enotslim]

The new bulb initially worked when I tested it in the fitting connected to the cable from the control unit but not inserted into the headlight assembly. I then reassembled the bulb into the headlight assembly and the bulb did not light. After disassembly and lots of swapping I traced the problem to the control unit that attaches to the bottom of the headlight assembly. This control unit initially worked with the new bulb but no longer works.

I can replace this control unit. However, I would like to know if I did something to damage the old unit when I inserted the new bulb into the headlight assembly or if this was just a coincidence. What should I avoid?

Confession - I had trouble inserting the new bulb into the headlight assembly. When I disassembled things the bulb separated from its plug and stayed behind in the assembly. Clearly it was not properly seated to begin with even though it lit. But the same bulb still works when connected to the other control unit.

I would appreciate any suggestions that prevent me from damaging a new control unit the way I may have damaged the old one.

Also, I'm confused about terminology. The faulty piece is variably called control unit and ballast. But the fitting that the bulb plugs in to is also called ballast. What are the correct names for these components (and what do they actually do)?

Thanks.