3-4 Shift Valve
WARNING: This page is about a different car, the 2008 Isuzu i-370, 2008 Isuzu i-290, 2008 GMC Canyon, and 2008 Chevrolet Colorado. However, it is still accessible from the selected car via links, so may be relevant.
With the signal A fluid pressure exhausted, the spring force moves the valve into the downshift position. In this position, the valve blocks the 3-4 signal fluid and the 4th signal fluid exhausts past the valve.