Vehicle Speed Sensor
WARNING: This page is about a different car, the 2005 GMC Yukon XL, 2005 GMC Yukon, 2005 Chevrolet Tahoe, 2005 Chevrolet Suburban, and 2005 Chevrolet Avalanche. However, it is still accessible from the selected car via links, so may be relevant.
One of the two speed sensors on the rear output shaft is the vehicle speed sensor (VSS) input to the powertrain control module (PCM). The PCM sends this information to the transfer case shift control module via the Class 2 serial data bus.