B2 Control 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.
Drive (19) fluid pressure is regulated through the B2 control valve into the B2 control 1 (30) fluid circuit. B2 control 1 (30) fluid pressure is routed through the U1 shift valve into the B2 control 2 (31) fluid circuit and on to the M1 shift valve where it is blocked by the valve in preparation for an upshift to second gear.