Conditions for Setting the DTC
WARNING: This page is about a different car, the 2010 GMC Sierra, 2010 GMC Cab & Chassis Sierra, 2010 Chevrolet Silverado, and 2010 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
The TCCM monitors the front axle switch signal circuit and the front axle actuator control circuit for unexpected voltages. The DTC sets if the TCCM detects a high voltage when a low voltage is expected, or a low voltage when a high voltage is expected.