Circuit/System Verification
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.
Ignition ON, observe the scan tool Park Assist Switch LED parameter while pressing and releasing the park assist disable switch. The parameter should change between On and Off.