Allison 3000 & 4000 Gen 4 Fault Code: P0963 Pressure Control Solenoid Main Mod Control Circuit High

DIAGNOSTIC RESPONSE:
None

CIRCUIT DESCRIPTION:
Pressure Control Main Mod solenoid is a normally closed solenoid used to modulate the transmission main pressure schedule. The Transmission Control Module (TCM) commands the solenoid ON when specific transmission and engine conditions are met. When the Main Mod solenoid is commanded ON, pressure is routed to the main regulator valve and lowers the main pressure schedule. The TCM sends control current to the Main Mod solenoid from High Side Driver 1 (HSD1) via wire 111. HSD1 is continuously ON unless the TCM detects a fault condition. The TCM regulates the amount of current to the Main Mod solenoid by switching the Main Mod solenoid’s low side driver ON and OFF. Wire 174 completes the circuit between the Main Mod solenoid and its low side driver. DTC P0963 indicates that the TCM has detected a failed high condition in the Main Mod 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 Main Mod solenoid low side driver has been detected in a failed high state.

ACTION TAKEN WHEN THE DTC SETS:
When DTC P0963 is active:
1. Main Modulation is inhibited.
2. DTC is sorted 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 P0963 can be caused by:
1. Main Mod issues such as:
– W174 short in chassis harness.
– W174 (terminal 8 of 20-way) short in internal transmission harness.
– Main Mod solenoid defective.
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.