3-2 Control Solenoid Valve
WARNING: This page is about a different car, the 2007 GMC Yukon XL, 2007 GMC Yukon, 2007 Chevrolet Tahoe, 2007 Chevrolet Suburban, and 2007 Chevrolet Avalanche. However, it is still accessible from the selected car via links, so may be relevant.
In second gear, the PCM energizes the normally closed solenoid. This opens the AFL fluid circuit to fill the 3-2 signal fluid circuit.