Torque Converter Clutch (TCC) Solenoid
WARNING: This page is about a different car, the 2007 Mercury Mariner and 2007 Ford Escape. However, it is still accessible from the selected car via links, so may be relevant.
The torque converter clutch (TCC) solenoid is a PWM style solenoid. The PWM solenoid is used to control the apply and release of the bypass clutch in the torque converter. By modulating the pulse width of the TCC solenoid, the pressure in the S4 circuit varies modulating the apply and release of the bypass clutch in the torque converter.