1-2 Shift Solenoid Valve
WARNING: This page is about a different car, the 2010 Pontiac G5 and 2010 Chevrolet Cobalt. 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.