Circuit/System Verification
WARNING: This page does not describe the selected car, but rather 8 other vehicles, including the 2012 GMC Yukon XL, 2012 GMC Yukon, 2012 Chevrolet Tahoe, 2012 Chevrolet Suburban, and 2012 Chevrolet Avalanche. However, it is still accessible from the selected car via links, so may be relevant.
Ignition ON, insert the key into the driver's door lock cylinder and observe the scan tool Door Key Cyl. Unlock Switch parameter while turning the key to the UNLOCK position, the parameter should change between Idle and Unlock.