M2 Shift Valve
WARNING: This page is about a different car, the 2009 Pontiac Torrent and 2009 Chevrolet Equinox. However, it is still accessible from the selected car via links, so may be relevant.
When S2 signal (15) fluid exhausts, spring force shifts the M2 shift valve to the released position, allowing direct clutch feed 2 (28) fluid to pass through the valve into the direct clutch (29) fluid circuit.