P0740 Torque Converter Clutch Solenoid Valve: Description

WARNING: This page is about a different car, the 2009 Nissan Maxima. However, it is still accessible from the selected car via links, so may be relevant.

The torque converter clutch solenoid valve is activated by the TCM in response to signals sent from the vehicle speed and accelerator pedal position sensors. Lock up piston operation will then be controlled.
Lock up operation, however, is prohibited when CVT fluid temperature is too low.
When the accelerator pedal is depressed (less than 2.0/8) in lock up condition, the engine speed should not change abruptly. If there is a big jump in engine speed, there is no lock up.