Allison 1000 & 2000 Gen 4 Fault Codes: P0742 Torque Converter Clutch System Stuck On

Allison 1000 & 2000 Gen 4 Fault Codes: P0742 Torque Converter Clutch System Stuck On

CIRCUIT DESCRIPTION:
The Transmission Control Module (TCM) uses data from the engine speed sensor and the turbine speed sensor to calculate the torque converter slip value. The TCM then compares this calculated slip value to a preset value in the TCM calibration.

CONDITIONS FOR RUNNING THE DTC:
1. DTC P0122, P0123, P0716, P0717, P0721, P0722, P0726, P0727, or P0743 (previously P1860) is not active.
2. The components are powered and ignition voltage is greater than 9V and less than 18V (12V TCM) or greater than 18V and less than 32V (24V TCM).
3. Engine speed is greater than 200 rpm for 5 seconds.
4. Transmission is in a valid forward range.
5. The torque converter clutch is OFF.

CONDITIONS FOR SETTING THE DTC:
DTC P0742 sets when the conditions listed below are present and the TCM detects converter slip speed between -5 and -40 rpm for over 2 seconds.
1. Transmission output speed is 100 rpm or higher.
2. Engine throttle percentage is 15 percent or higher.
3. Engine torque is 130 N-m or higher.
4. Engine and turbine speed are under 5500 rpm.

ACTION TAKEN WHEN THE DTC SETS:
1. Illuminate CHECK TRANS light on second occurrence.
2. Response is calibration dependent.
3. If response is disabled, no action is performed.
4. If enabled, when DTC is set before or during a shift, response is a shift to neutral. If DTC is set after shifting is complete, transmission shifts to neutral or 1st range. While response is active, if the selector is moved to a forward range, transmission shifts to neutral or 1st range. If the selector is moved to reverse, the transmission shifts to neutral or reverse.

CONDITIONS FOR CLEARING THE DTC/CHECK TRANS LIGHT:
A Scan Tool may be used to clear the code from the TCM history. The TCM automatically clears the DTC from the TCM history if the vehicle completes 40 warm-up cycles without the DTC recurring.

DIAGNOSTIC AIDS:
This DTC sets when converter slip speed indicates the TCC is staying applied when it should be released for a period of time that is calibration dependent. This may indicate an internal failure of the TCC or a stuck or sticking TCC valve.