#5 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 fluid passes through the variable low and 1-2 reverse and 4th clutch regulator valve into the PS5 fluid passage. PS5 fluid opens the normally closed #5 pressure switch, signaling the TCM that the transmission is in EVT Mode High.