Primary Pressure Regulator 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.
Reverse (22) fluid pressure also exhausts from the primary regulator valve plunger, allowing line (2) pressure to return to the normal operating range as in PARK, NEUTRAL and DRIVE gear ranges.