[litteng]

i just pulled a set (on my passat) where i was having problems on startup, one or the other might not fire. turned out to be a low voltage problem which was easily remedied, so check the voltage to the ballast, then try direct to battery connection to bypass all the car electrical system.

i had a bulb burn out recently too. and the only way to confirm a bulb or ballast is to swap with know good parts either side to side or with a buddies car using the same type bulb.

if these are the factory litronics its probably a D2S bulb which is common to number of OEM HID systems, you may have the same bulb in another vehicle