Circuit/System Description
WARNING: This page is about a different car, the 2010 GMC Sierra and 2010 Chevrolet Silverado. However, it is still accessible from the selected car via links, so may be relevant.
In 4WD Auto mode, the transfer case shift control module (TCCM) monitors the front and rear wheel speed sensors for slip. If the TCCM detects slip, and is unable to correct for a difference between the front and rear speed sensors, it will command the transfer case to apply the clutch. In addition, the TCCM tests for clutch pack wear by performing a high side kiss point check at power down and comparing it to the incremental position sensor reading.