1-2 Shift 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.
Spring force and low fluid pressure in the 2-3 shift solenoid (SS) valve hold the 1-2 shift valve in the upshifted position. The 1-2 shift valve allows orificed drive fluid to pass through the valve into the second clutch circuit. Second clutch fluid is then routed to the 1-2 accumulator piston and to the second clutch piston in order to apply the clutch.