Drive her to a dealer and get her scanned. My X3 does it to me the same exact symptom, and left no error message at all. However, when I went to this indy, a very well equipped indy, they scanned my X and pin pointed that exact sensor within 10 minutes. Basically he's sending signal to each sensor to test them running, and the bad one will just keep sending back bad signals.

My X3 is N52 by the way. Good Luck!

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01' 3.0i E53 (M54) with 164,000 miles
07' 3.0si E83 (N52) with 134,000 miles
08' 3.0si E70 (N52) with 91,000 miles