Pressure Control (PC) Solenoid
WARNING: This page is about a different car, the 2008 Buick LaCrosse and 2008 Buick Allure. However, it is still accessible from the selected car via links, so may be relevant.
During the downshift, except for a coastdown, the PCM senses the increase in throttle position or engine load and increases the PC solenoid duty cycle. The increase in duty cycle increases output fluid pressure from the PC solenoid, thereby increasing torque signal fluid pressure at the torque signal regulator valve.