Transfer Case Speed Sensors
WARNING: This page is about a different car, the 2002 Oldsmobile Bravada. However, it is still accessible from the selected car via links, so may be relevant.
There are three speed sensors on the automatic transfer case (ATC), two on the rear output shaft and one on the front output shaft. Each speed sensor is a permanent magnet (PM) generator. The PM generator produces a pulsing AC voltage. The AC voltage level and number of pulses increases as speed increases.