As long as this thread got resurrected by a spammer, I'll post my recent experiences on my wife's 90k-mile 2007 328ixDrive Sport Auto.
It had thrown a fault at the beginning of last winter and a quick scan showed low voltage at two terminals. We'd only had the car for a short time so I figured we'd just replace the battery. And that seemed to clear the problem until a month ago when up popped the dreaded "4x4 inactive!" fault. Process of elimination and the experience of others led me to replacing the servo motor ($400 or so from FCPEuro). That changed nothing. So I took it to my BMW dealer where I work and had one of the techs and the shop foreman do a diagnosis. They got no response from the transfer case during the test program so told me I needed a new transfer case. Ouch!
Well, we got such a good deal on the car I figured we'd bite the bullet and replace the transfer case and move on. After the new transfer case arrived and was installed, there was no change in the faults. Speculation was that the control unit was bad. They checked under the carpet for water damage and, finding none, suggested that the bad transfer case may have caused the control unit to fail. Sounded suspect to me but these are my guys so we ordered a new control unit for around $600. That cured the problem. Now I work with these guys every day so I didn't want to be "that guy" and reinstall the old transfer case to prove I was right, so my wife is now driving the car and enjoying being able to see her clock and temp gauge once again. I figure we're now up to what the car would have retailed for and cognitive dissonance has let me rationalize the entire repair cost and not lose any sleep over it.
So, it is entirely possible that I now have two perfectly good servo motors. One brand new, and the other with 90k-miles. It is also possible I have a perfectly good transfer case with 90k-miles on it. But I'll never know. Any market for these items, given the circumstances???
