Conditions for Setting the DTC

WARNING: This page does not describe the selected car, but rather 6 other vehicles, including the 2003 GMC Yukon XL, 2003 GMC Yukon, 2003 Chevrolet Tahoe, 2003 Chevrolet Suburban, and 2003 Chevrolet Avalanche. 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.