1-2 Shift Valve
WARNING: This page is about a different car, the 2008 GMC Sierra and 2008 Chevrolet Silverado. However, it is still accessible from the selected car via links, so may be relevant.
Signal A fluid pressure moves the valve against the spring force and into the downshift position. In this position, Lo fluid from the manual valve is routed into the Lo/1st fluid circuit and D4 fluid is blocked from entering the 2nd fluid circuit. The 2nd fluid exhausts through an orifice and an annulus exhaust port past the valve. This orifice (#26) helps control the 2-4 band release during a 2-1 downshift.