Transmission Control Module (TCM) - NAG1
P0741-TORQUE CONVERTER CLUTCH CIRCUIT PERFORMANCE
For a complete wiring diagram, refer to the Wiring Information.
Theory of Operation
The torque converter contains an internal Torque Converter Clutch (TCC) which is controlled by the Transmission Control Module (TCM) to maintain slip (engine speed versus transmission input speed) to optimize fuel economy under specific speed and throttle conditions. For fault determination, the TCM monitors the amount of torque converter slip ONLY when the TCC is in Slip Mode operation. During Slip Mode, the slip speed is expected to be within a predetermined range. If the Torque Converter Clutch (TCC) does not receive adequate hydraulic pressure for any reason, or if the internal clutch is damaged, the TCC will not be able to control to the predetermined slip value. Therefore, if the torque converter slip is more than expected for a predetermined amount of time, the DTC will set.
- When Monitored:
Ignition on, TCM not in initialization phase, no input speed sensor 1 or 2 (N2-N3) DTCs, no CAN bus or ECM DTCs, no CAN engine speed signal or engine torque signal not implausible DTCs, engine speed greater than 450 rpm, no shift in progress, gear 1, 2, 3, 4 or 5 engaged, and the TCM torque converter status is SLIP
- Set Condition:
While in Slip Mode operation, the TCM detects TCC slippage greater than a calibrated value.
Always perform the NAG1 Pre-Diagnostic Troubleshooting procedure before proceeding NAG1 Pre-Diagnostic Troubleshooting Procedure.
1. CHECK FOR RELATED DTCS
1. Ignition on, engine off.
2. Using the scan tool, check DTCs.
Are there any Speed Sensor and/or TCC DTCs present?
Yes
- Refer to the Transmission DTC based Diagnostics and perform the appropriate diagnostic procedure.
No
- Go To 2
2. CHECK THE TORQUE CONVERTER CLUTCH PERFORMANCE
1. Operate the vehicle until the transmission sump temperature is to greater than 65° C (150° F).
2. Using the shifter lever, select third gear.
3. Accelerate the vehicle to third gear and hold.
4. With the scan tool, verify the TCC status is reading "SLIP".
5. Monitor TCC Desired Slip and TCC Actual Slip.
6. Operate the vehicle at 30 mph while maintaining third gear.
7. Lightly depress the accelerator and hold the throttle position steady between 40 and 50%.
8. Slowly accelerate vehicle using steady throttle without causing TCC Status to read "OPEN".
NOTE: If at any time during the above test the TCC Status changes from SLIP to OPEN, or the vehicle downshifts to a lower gear, the test is invalid and must be performed again.
9. Compare TCC Actual Slip and TCC Desired Slip during steady throttle acceleration with TCC Status continually reading "SLIP".
Does TCC Actual Slip exceed TCC Desired Slip by more than 60 rpm while accelerating at a steady throttle and staying in SLIP mode?
Yes
- Inspect transmission fluid for water contamination.
- Inspect internal transmission. Pay particular attention to the components related to the TCC such as possible missing Input Shaft Seal Ring, Lockup Control Valve sticking in its bore, and/or a leaking TCC Solenoid.
- If no internal transmission issues found, replace the Torque Converter.
- Perform NAG1 TRANSMISSION VERIFICATION TEST NAG1 Transmission Verification Test.
No
- Go to 3
3. TRANSMISSION CONTROL MODULE
1. Using the schematics as a guide, check the Transmission Control Module (TCM) pins, terminals, and connectors for corrosion, damage, or terminal push out. Pay particular attention to all power and ground circuits. Check for Service Bulletins for any possible causes that may apply. If no problems are found, replace and program the TCM.
2. Perform TCC slip test to verify repair.
NOTE: To set P0741 fault, TCM must encounter three events where the TCM cannot control TCC Actual Slip to TCC Desired Slip in a single key cycle.
Does the DTC reset?
Yes
- Inspect transmission fluid for water contamination
- Inspect internal transmission. Pay particular attention to the components related to the TCC such as possible missing Input Shaft Seal Ring, Lockup Control Valve sticking in its bore, and/or a leaking TCC Solenoid.
- If no internal transmission issues are found, replace the Torque Converter.
- Perform NAG1 TRANSMISSION VERIFICATION TEST NAG1 Transmission Verification Test.
No
- Test complete.