P0740 Cadillac Torque Converter Clutch Circuit Malfunction
– Dirty transmission fluid
– Faulty torque converter clutch solenoid valve
– Torque converter clutch solenoid valve harness is open or shorted
– Torque converter clutch solenoid valve circuit poor electrical connection
– Transmission shift shock
– Vehicle may not shift into the highest gear
The torque converter clutch solenoid valve is activated, with the gear in D4, by the Transmission Control Module (TCM) in response to signals sent from the vehicle speed and the Engine Control Module (ECM). Lock-up piston operation will then be controlled. When the torque converter clutch solenoid valve is activated, the torque converter lockup clutch will engage creating a 1 to 1 RPM ratio between the transmission input shaft and the rotational speed of the torque converter.
Lock-up operation, however, is prohibited when A/T fluid temperature is too low.
When the accelerator pedal is depressed (less than 2/8) 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.