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Discussion Starter #1
Friend's 2009 E90 335d 94,000mi

A search turned nothing up, but...

Car was in minor accident (scrapes and scratches only, but the right H/L outer lens was scratched) and when it came back from the body shop the new right adaptive H/L system only pointed down, so another new H/L assembly was fitted, which fixed that problem.

Now (since the body shop anyway) the headlights are good and bright with the ignition on position 2, but with the car not running (system voltage 12.5v on a charged battery).

But if you start the car, both H/L xenons start flickering badly. I thought maybe the bulbs were shot, so installed 2 new ones, but there was no change.

With the engine running system voltage shows 14.5-14.7v which seems awfully high to me. I would expect 13.8-14.4 maybe.

Using a friend's Bluetooth scanner/programmer, I can get into the system and adjust the lighting circuit voltage, but even with it set at or even below the same 12.5v that works perfectly with the engine NOT running, with the engine running and lighting voltage at 12.5v the headlights STILL flicker like mad.

So it seems maybe the problem is related to the alternator and charging circuit? I seriously doubt both light ballasts decided to die at the same time, and I don't think it's a bulb problem (both the old and new bulbs flicker the same) .

Is their a failure mode in the alternator (bad diode/voltage hash or spikes/AC hum on the output line) that could be causing the lights to flicker even when the lighting voltage is reduced to 12 or 12.5v?

Oh, yes, NONE of the other lights on the car (incandescent or LED) flicker under any circumstances-JUST the xenons.

Any ideas?

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