Allison 3000 & 4000 Gen 4 Fault Code: P0634 TCM Internal Temperature Too High

DIAGNOSTIC RESPONSE:
SOL OFF (hydraulic default)

CIRCUIT DESCRIPTION:
The Transmission Control Module (TCM) is equipped with an internal temperature sensor mounted directly to its circuit board. The TCM takes action to protect against damage from overheating.

CONDITIONS FOR RUNNING THE DTC:
After TCM initializes normally and engine speed is above 200 rpm for more than 5 seconds, this DTC test will run at 0.5 second intervals.

CONDITIONS FOR SETTING THE DTC:
DTC P0634 sets if the TCM internal temperature is greater than or equal to 140°C (248°F) for 10 seconds while engine running.

ACTION TAKEN WHEN THE DTC SETS:
1. The TCM does not illuminate the CHECK TRANS light.
2. DTC is stored in the TCM history.
3. The TCM commands OFF all solenoids (SOL OFF).
4. TCM shutdown.

CONDITIONS FOR CLEARING THE DTC/CHECK TRANS LIGHT:
Use the diagnostic tool to clear the DTC 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:
DTC P0634 may be caused by:
1. Defective TCM.
2. Debris on TCM.
3. External heat source such as vehicle exhaust in vicinity of TCM.

Clean the TCM if necessary. Excessive road debris will reduce the effectiveness of the heat sink on the TCM and could cause internal temperature to rise.

TCM Substrate Temperature is available on the diagnostic tool Data Monitor grid. Prior to ‘Connect’ for the diagnostic tool, check the ‘Troubleshoot Specific Problem’ box under ‘Connection Options’ and then check the ‘Sensor, Voltage, Ohms, and Counts Data’ box.

Review applicable information in Control System and Transmission Specifications to find additional circuit specifications, system and connector diagrams, and troubleshooting tips.