Conditions for Setting the DTC: P0843
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.
The TCM detects that PS1 is OFF or High when shift solenoid 1 (SS1) is commanded ON for 1 second.