Torque Converter Clutch
WARNING: This page is about a different car, the 2010 Pontiac G5 and 2010 Chevrolet Cobalt. However, it is still accessible from the selected car via links, so may be relevant.
The PCM commands TCC release prior to initiating a 4-3 downshift. When the TCC is in the release position, release fluid pressure is routed to the pressure switch assembly. This fluid pressure signals the PCM that the TCC is in the release position. The TCC is not applied under normal operating conditions in Third gear.