Circuit/System Verification
WARNING: This page is about a different car, the 2009 GMC Sierra, 2009 GMC Cab & Chassis Sierra, and 2009 Chevrolet Silverado. However, it is still accessible from the selected car via links, so may be relevant.
With PTO enabled, use a scan tool to shutdown the engine using the Engine Shutdown special function in the PTO module. The engine should shutdown.