Conditions for Setting the DTC

WARNING: This page is about a different car, the 2003 GMC Sierra, 2003 GMC Cab & Chassis Sierra, 2003 Chevrolet Silverado, and 2003 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.

The transfer case shift control module tries to unapply, turn OFF the lock solenoid by grounding the motor control circuit.
If the module does not sense the battery voltage at the motor lock control circuit prior to applying the motor lock, the DTC sets.
Transfer Case Lock output reads back as a high voltage when a low voltage is expected.