Solenoid Relay 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.
45 enable (51) fluid pressure exhausts from the solenoid relay valve, passes through the U2 shift valve into the S4 signal (17) fluid circuit and continues on to the 3-4, 4-5 SS valve assembly where it exhausts into the sump.