#1 Pressure Switch
WARNING: This page is about a different car, the 2008 GMC Yukon and 2008 Chevrolet Tahoe. However, it is still accessible from the selected car via links, so may be relevant.
Actuator feed limit fluid passes through the hybrid low, 1-2 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.