M1 Shift Valve
WARNING: This page is about a different car, the 2003 Saturn Vue. However, it is still accessible from the selected car via links, so may be relevant.
When reverse inhibit (52) fluid exhausts, spring force shifts the M1 shift valve to the released position. This allows B2 control 2 (31) fluid to pass through the valve into the second clutch (32) fluid circuit.