Possible causes

– Low transmission fluid level
– Dirty transmission fluid
– Faulty torque converter clutch solenoid valve
– Torque converter clutch solenoid valve harness or connectors
– Torque converter clutch solenoid valve circuit is open or shorted
– Transmission internal mechanical problem

Tech notes

When the a transmission solenoid is stuck on, in most cases the problem is not the electrical part of the solenoid; the problem is foreign material obstructing the mechanical function of the solenoid or the flow of the fluid through the transmission valve body. If the transmission fluid is very dirty, it is recommend changing the transmission fluid and if possible removing the transmission pan for further diagnosis. Excessive debris or metal particles on the transmission pan could be an indication that there is a transmission mechanical failure and that the transmission will need to be rebuilt or replaced.

When is the code detected?

When the Powertrain Control Module (PCM) no longer provides a ground path, the Torque Converter Clutch (TCC) solenoid valve de-energizes and apply fluid exhausts, releasing the TCC.
When the PCM detects low torque converter slip when the PCM commands the TCC OFF, then is sets the P0742 code.

Symptoms

– Engine Light ON (or Service Engine Soon Warning Light)

P0742 CHEVROLET Description

The Torque Converter Clutch (TCC) solenoid valve is a normally-open exhaust valve that is used with the Torque Converter Clutch Pulse Width Modulation (TCC PWM) solenoid valve in order to control fluid acting on the converter clutch apply valve. The TCC solenoid valve attaches to the transmission case assembly extending into the pump cover. When grounded (energized) by the Powertrain Control Module (PCM), the TCC solenoid valve stops converter signal oil from exhausting. This causes converter signal oil pressure to increase and move the converter clutch apply valve against spring force and into the apply position. In this position, release fluid is open to an exhaust port and converter feed fluid fills the apply fluid circuit. The converter feed fluid applies the TCC.

CHEVROLET Technical Service Bulletins for P0742 code