Allison 3000 & 4000 Gen 4 Fault Code: P2764 TCC PCS Control Circuit Low

DIAGNOSTIC RESPONSE:
7-speed: Allow 2 through 6, N, R. Inhibit TCC operation

CIRCUIT DESCRIPTION:
The Torque Converter Clutch (TCC) Pressure Control Solenoid (PCS) is a normally closed solenoid used to apply the lockup clutch when specific engine and turbine speed conditions are met. The Transmission Control Module (TCM) commands the solenoid ON to produce hydraulic pressure in the lockup clutch apply circuit. When the TCC solenoid is commanded OFF, lockup clutch pressure is exhausted. The TCM sends control current to the TCC solenoid from High Side Driver 3 (HSD3) via wire 131. HSD3 is continuously ON unless the TCM detects a fault condition The TCM regulates the amount of current to the TCC solenoid by switching the TCC solenoid low side driver ON and OFF. Wire 137 completes the circuit between the TCC solenoid and its low side driver. DTC P2764 indicates that the DTC has detected a short-to-ground condition in the low side of the TCC solenoid electrical circuit.

CONDITIONS FOR RUNNING THE DTC:
TCM initialized normally and engine speed above 200 rpm.

CONDITIONS FOR SETTING THE DTC:
This DTC sets when the TCM detects the TCC solenoid low side driver in a failed low state.

ACTION TAKEN WHEN THE DTC SETS:
When DTC P2764 is active :
1. The TCM inhibits TCC engagement.
2. DTC is stored in the TCM history.
3. The CHECK TRANS light illuminates.
4. The TCM freezes shift adapts (DNA).

CONDITIONS FOR CLEARING THE DTC:
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 failure.

DIAGNOSTIC AIDS:
DTC P2764 can be caused by:
1. TCC solenoid circuit issues such as:
– W137 shorted to another wire or to chassis ground in chassis harness.
– W137 (terminal 12 of 20-way) shorted to another wire in internal transmission harness or to the
control valve module.
2. Broken or defective connector assemblies allowing pushed back pins to short together.
3. Unlocked connectors, missing seal plugs allowing moisture in connectors.
4. Defective TCM.

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