1-2 Shift Solenoid (SS) Valve
WARNING: This page is about a different car, the 2009 GMC Canyon and 2009 Chevrolet Colorado. However, it is still accessible from the selected car via links, so may be relevant.
Energized (ON) as in Neutral, the normally open solenoid is closed and blocks signal A fluid from exhausting through the solenoid. This maintains pressure in the signal A fluid circuit.