Allison 3000 & 4000 Gen 4 Fault Code: P2718 Pressure Control Solenoid 4 (PCS4) Control Circuit Open

DIAGNOSTIC RESPONSE:
DNS, SOL OFF (hydraulic default)

CIRCUIT DESCRIPTION:
Pressure Control Solenoid 4 (PCS4) is a normally closed solenoid used to apply the C4 clutch in 2nd and 6th ranges. The Transmission Control Module (TCM) commands the solenoid ON to produce hydraulic pressure in the clutch apply circuit. When PCS4 is commanded OFF, the clutch pressure is released. The TCM sends control current to PCS4 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 PCS4 by switching PCS4 low side driver ON and OFF. Wire 155 completes the circuit between PCS4 and its low side driver. DTC P2718 indicates that the TCM has detected an open condition in the PCS4 electrical circuit. The open condition may exist in the high side (wire 111) or low side (wire 155).

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 PCS4 low side driver has been detected in a failed open state.

ACTION TAKEN WHEN THE DTC SETS:
When DTC P2718 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 (R), the transmission remains in Reverse (R) 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 from the TCM history if the vehicle completes 40 warm-up cycles without failure.

DIAGNOSTIC AIDS:
DTC P2718 can be caused by:
1. PCS4 issues such as:
– W155 high resistance or an open circuit in chassis harness.
– W155 (terminal 2 of 20-way) high resistance or an open circuit in internal transmission harness.
– PCS4 defective.
2. Unlocked connectors, expanded terminals, poor pin crimps or unlocked pins causing high resistance or open circuit.
3. Defective TCM.

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