[s-cars] RPM Sensor?

[Dave Forgie]

Chris:  There are actually two sensors in the same area: The G4 Crank 
Position Sensor (which looks for a specific pin location) and the G28 Engine
 Speed Sensor (which reads the passing of the flywheel teeth and 
translates it a signal for the computer to compute RPM).  They can (but 
rarely) go bad.  There have been a few cases on AudiWorld.  Check the 
link to one of my posts there on the subject.

http://forums.audiworld.com/s4s6/msgs/116988.phtml

HTH 

Dave F.