2-3 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.
High fluid pressure at the 2-3 shift solenoid (SS) valve holds the 2-3 shift valve in the upshifted position. This allows coast clutch fluid to pass through the valve. Coast clutch fluid is then routed to the coast clutch piston and applies the clutch.