#9 Reverse Shift Restrict Ball Check 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.
Exhausting 3rd gear band apply (46) fluid seats the reverse shift restrict ball check valve against the servo release (43) fluid passage and enters the servo apply (45) fluid passage.