Do your lights look like the attached picture? I believe these are what my original 04 XC70 came with, but previous owner did a hack job to replace them with normal halogen assemblies and bulbs. Pretty sure there is no hi/low - it's just the single HID that is adjusted up to have them shine higher, ...

Marked for inclusion in the Volvo Repair Database VRD.

Thanks everyone! Lot of good leads to check.