$38 (P0740) - Torque Converter Clutch Control Circuit

Name of code: $38 (P0740) - Torque Converter Clutch Control Circuit

When monitored: During Electronically Modulated Converter Clutch (EMCC)

Set condition:
a) The transmission must be in EMCC, with the input speed greater than 1750 RPM. The TCC/L-R solenoid must achieve it's maximum duty cycle and still not be able to pull the engine speed within 60 RPM of input speed.
b) If the transmission is in FEMCC and the engine can slip the TCC by more than 100 RPM (Engine speed - Input speed) for 10 seconds.

The code will be set if one of these events happens three times at a throttle angle less than 30 degrees.

Theory of operation: When in 2nd, 3rd, or 4th gear, the torque converter clutch (TCC) can be locked when certain conditions are met. The TCC piston is electronically modulated by increasing the duty cycle of the L-R/TCC solenoid until the torque converter slip difference (difference between engine and turbine speed) is within 60 RPM. Then the L-R/TCC solenoid is fully energized (FEMCC / 100% duty cycle). Torque converter slip is monitored in FEMCC to ensure adequate clutch capacity.

Transmission Effects: EMCC will still be available after code is set. MIL will illuminate after 5 minutes of accumulated slip in FEMCC. The trans will attempt normal operation (no limp-in) even after the MIL is illuminated.

Possible causes:
- Worn pump bushing and/or failed torque converter - both should be replaced during a rebuild with code 38 present
- Valve body - lock-up accumulator diameter out of spec. Possible but not likely.