#1 Pressure Switch
WARNING: This page is about a different car, the 2009 Saturn Vue. However, it is still accessible from the selected car via links, so may be relevant.
Actuator feed limit/backfill fluid pressure passes through the 1-3 reverse clutch regulator valve into the PS1 fluid passage. PS1 fluid opens the normally closed #1 pressure switch, signaling the TCM that the transmission is in EVT Mode High.