The Torque Converter Clutch (TCC) establishes a connection between the engine output and the transmission input. This connection results in fuel efficiency, in addition to reducing transmission fluid temperature. Locking the converter housing to the turbine shaft prevents slippage from occurring because transmission slippage consumes energy when the coupling is made. The TCC is controlled by an electronic solenoid.
When the diagnostic code P2757 OBD2 is stored, it is because the Powertrain Control Module (PCM) has found a problem in the Torque Converter Clutch pressure control solenoid circuit.