Torque Converter Clutch
WARNING: This page is about a different car, the 2003 Pontiac Grand Prix, 2003 Chevrolet Malibu, and 2003 Buick Century. However, it is still accessible from the selected car via links, so may be relevant.
See TORQUE CONVERTER CLUTCH PULSE WIDTH MODULATION SOLENOID VALVE under TRANSMISSION under MISCELLANEOUS CONTROLS.