1-2 Shift Solenoid (SS) Valve
WARNING: This page is about a different car, the 2009 Cadillac DTS. However, it is still accessible from the selected car via links, so may be relevant.
De-energized (turned OFF) by the PCM, the 1-2 SS valve exhausts fluid through the solenoid valve. This creates a low fluid pressure from the 1-2 SS valve in the circuit. This low solenoid pressure allows the 1-2 shift valve to move to the upshifted position. The 3-4 shift valve moves to the downshifted position.