Conditions for Setting the DTC
WARNING: This page is about a different car, the 2007 GMC Sierra and 2007 Chevrolet Silverado. However, it is still accessible from the selected car via links, so may be relevant.
DTC P0877 sets when P (PARK), N (NEUTRAL), or a forward range is selected and the PS4 state remains in the mechanically closed/electrically ON position for greater than 1.0 second.