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.
In first gear, the PCM energizes the 1-2 shift solenoid valve and the 1-2 signal fluid pressure acts on the 1-2 shift valve.