Front Propshaft Speed Sensor
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.
The transfer case shift control module converts the pulsating AC voltage from the front transfer case speed sensor to front propshaft speed in RPM to be used for calculations, and to monitor the difference between the front and rear sensor speed. It is also used in the AUTO (Adapt) mode of operation to determine the amount of slip and the percent of torque to apply to the front axle. The front propshaft speed can be displayed with a scan tool.