Allison 3000 & 4000 Gen 4 Fault Code: P2727Pressure Control Solenoid 1 (PCS1) Control Circuit Open

DIAGNOSTIC RESPONSE:
DNS, SOL OFF (hydraulic default)

CIRCUIT DESCRIPTION:
Pressure Control Solenoid 1 (PCS1) is a normally open solenoid used to apply the C1 clutch in 1st and 4th range. The Transmission Control Module (TCM) commands the solenoid OFF to produce hydraulic pressure in the clutch apply circuit. When PCS1 is commanded ON, the C1 clutch is released. The TCM sends control current to PCS1 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 PCS1 by switching PCS1 low side driver ON and OFF. Wire 136 completes the circuit between PCS1 and its low side driver. DTC P2727 indicates that the TCM has detected an open condition in the PCS1 electrical circuit. The open condition may exist in the high side (wire 171) or low side (wire 136).

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 PCS1 low side driver has been detected in a failed open state.

ACTION TAKEN WHEN THE DTC SETS:
When DTC P2727 is active:
1. If failure occurs while in a forward range, then the transmission shifts to another forward range. If failure occurs while in Neutral (N), transmission remains in Neutral (N). If failure occurs while in Reverse (R), 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 P2727 can be caused by:
1. PCS1 issues such as:
– W136 high resistance or an open circuit in chassis harness.
– W136 (terminal 4 of 20-way) high resistance or an open circuit in internal transmission harness.
– PCS1 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.