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.
The 1-2 SS valve de-energizes, allowing fluid pressure from the 1-2 SS valve (acting on the end of the 3-4 shift valve) to exhaust through the solenoid. With low fluid pressure in the 1-2 SS valve, spring force acting on the opposite end of the valve moves the 3-4 shift valve.