^ this would be my guess. Same thing happened to my car - the wire at the connector was starting to go... sometimes it would work, othertimes not until it eventually failed completely and the warning was on all the time.
1992 BMW 325i (CHUMPCAR #296 - build in progress)
1992 3.0L M52 325i (ex-daily driver - track car only)
2002 330Ci (ex-daily driver - sold!)
Check out my e36 track car build