1-2 Shift Solenoid Valve
WARNING: This page is about a different car, the 2004 Pontiac Sunfire, 2004 Chevrolet Classic, and 2004 Chevrolet Cavalier. However, it is still accessible from the selected car via links, so may be relevant.
The PCM de-energizes the normally open solenoid valve and the 1-2 signal fluid exhausts.