#3 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.
With the actuator feed limit/backfill passage closed at the shift solenoid valve - mode A, actuator feed limit/backfill fluid pressure increases to actuator feed limit pressure. PS3 fluid pressure, fed by actuator feed limit/backfill pressure through the variable hi and 2-3-4 clutch regulator valve, also increases. PS3 fluid opens the normally closed #3 pressure switch, signaling the TCM that the transmission is in EVT Mode High.