Allison 3000 & 4000 Gen 4 Fault Code: P0966 Pressure Control Solenoid 2 (PCS2) Control Circuit Low

DIAGNOSTIC RESPONSE:
DNS, SOL OFF (hydraulic default)

CIRCUIT DESCRIPTION:
Pressure Control Solenoid 2 (PCS2) is a normally open solenoid used to apply the C2 clutch in 4th – 6th range, and the C3 clutch in Reverse (R). The Transmission Control Module (TCM) commands the solenoid OFF to produce hydraulic pressure in the clutch apply circuit. When PCS2 is commanded ON, the C2 clutch is released. The TCM sends control current to PCS2 from High Side Driver 2 (HSD2) via wire 171. HSD2 is continuously ON unless the TCM detects a fault condition. The TCM regulates the amount of current to PCS2 by switching PCS2 low side driver ON and OFF. Wire 152 completes the circuit between PCS2 and its low side driver. DTC P0966 indicates that the TCM has detected a failed low condition in the PCS2 electrical circuit. The condition may exist in the high side (wire 171) or low side (wire 152).

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 PCS2 low side driver has been detected in a failed low state.

ACTION TAKEN WHEN THE DTC SETS:
When DTC P0966 is active:
1. If failure occurs while in a forward range, then shifts to another forward range. If failure occurs while in Neutral (N), the transmission remains in Neutral (N). If failure occurs while in Reverse, the transmission remains in Reverse or shifts to Neutral (N). Once range is attained, transmission will be locked in range. There is no response to shift selector requests.
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 form the TCM history if the vehicle completes 40 warm-up cycles without failure.

DIAGNOSTIC AIDS:
DTC P0966 can be caused by:
1. PCS2 issues such as:
– W152 shorted to another wire or ground in chassis harness.
– W152 (terminal 5 of 20-way) shorted to another wire or ground in internal transmission harness.
– PCS2 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.