Reverse, 1st Shift Solenoid (SS) Valve Assembly (S1)
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.
The reverse, 1st SS valve assembly is energized, causing fluid pressure to build-up in the S1 signal (14) fluid circuit.