Thanks RocketyMan! I didn't know most of that. Yes, mdecoder does report "S216 Hydro steering-servotronic"

EDIT: I have had the trifecta of lights in the past, although not currently. A local BMW specialist had indicated that it looked like an intermittently malfunctioning DSC (from memory), although he said it's usually one of a few other issues but ruled those out in my case. I'd picked up a used controller (still attached to the back of the donor ABS unit), but was waiting to put it in (and then have it recoded) until the next time the intake manifold has to come off. In the meantime, the trifecta hasn't been around lately and AWD had been working quite well in two recent snow storms, the first on 19" summer tires before the PS failed, and the second on 17" winter tires after the PS failed.

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2008 X3 (E83-LCI) 3.0si M-Sport
2004 X5 (E53-LCI) 4.4i M-Sport
1994 318i (E30-LCI) race car - sold