Pressure Control Solenoid (PCS) 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.
Controlled by the PCM, the PCS valve regulates the filtered actuator feed fluid pressure which acts on the end of the torque signal regulating valve.