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Allison - Automatic Transmission




DTC P2727, P2729, or P2730

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (Diagnostic System Check - Vehicle) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Strategy Based Diagnosis) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Diagnostic Procedure Instructions) provides an overview of each diagnostic category.

DTC Descriptor
DTC P2727
- Pressure Control (PC) Solenoid 1 Open

DTC P2729
- Pressure Control (PC) Solenoid 1 Control Circuit Low Voltage

DTC P2730
- Pressure Control (PC) Solenoid 1 Control Circuit High Voltage

Diagnostic Fault Information





Circuit/System Description

The Pressure Control Solenoid 1 (PCS1) is a solenoid that controls pressure which is proportional to the current. The transmission fluid pressure from PCS1 is directed to another valve which regulates the transmission fluid flow and pressure through shift valves that allows it to engage different clutches.

The transmission control module (TCM) provides B+ to PCS1, the torque converter clutch (TCC) solenoid, and the main modulation/line pressure control solenoid (MAIN MOD) through a separate solid state device called high side driver 1 (HSD1). The TCM uses a low side driver to control the current flow to the PCS1. The TCM controls the current to the solenoid by changing the amount of time that the low side driver is on.

Conditions for Running the DTC

* DTC P0657, P0658, or P0659 is not set.
* Battery voltage is between 9-18 V.
* Engine speed is greater than 200 RPM for 4 seconds.
* HSD1 is commanded ON.

Conditions for Setting the DTC

P2727

The TCM detects an open circuit on the PCS1 control circuit for 1 second.

P2729

The TCM detects a short to ground on the PCS1 control circuit for 1 second.

P2730

The TCM detects a short to voltage on the PCS1 circuit for 1 second.

Action Taken When the DTC Sets

* DTCs P2727, P2729, and P2730 are Type A DTCs.
* If the DTC sets while in a forward gear, the TCM commands 1st, 3rd, or 5th gear.

Conditions for Clearing the DTC

DTCs P2727, P2729, and P2730 are Type A DTCs.

Diagnostic Aids

P2727
* You may have to drive the vehicle in order to experience a condition.
* If DTC P2727 is accompanied by DTC P0960 and/or DTC P2761 the open is most likely in the HSD1 circuit.

P2729 and P2730

You may have to drive the vehicle in order to experience a condition.

Reference Information
Schematic Reference

Automatic Transmission Controls Schematics (Allison - Automatic Transmission)
Connector End View Reference

* Component Connector End Views (Connector End Views By Name)
* Inline Harness Connector End Views (Connector End Views By Number)

Description and Operation

* Transmission General Description (Transmission General Description)
* Transmission Component and System Description (Transmission Component and System Description)
* Electronic Component Description (Electronic Component Description)

Electrical Information Reference

* Circuit Testing (Circuit Testing)
* Connector Repairs (Connector Repairs)
* Testing for Intermittent Conditions and Poor Connections (Testing for Intermittent Conditions and Poor Connections)
* Wiring Repairs (Wiring Repairs)

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions (Powertrain Diagnostic Trouble Code (DTC) Type Definitions)
Scan Tool Reference

Control Module References (Control Module References) for scan tool information

Circuit/System Verification

1. Ignition ON, engine OFF, command the PC Solenoid 1 ON and OFF with a scan tool. Observe the scan tool PC Sol. 1 Pressure Command parameter. The PC Sol. 1 Pressure Command parameter should change from 0 kPa (0 psi) to 1,600 kPa (232 psi).
2. Operate the vehicle within the Conditions for Running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.

Circuit/System Testing

1. Ignition OFF, disconnect the X175 harness connector at the transmission.
2. Ignition ON, engine OFF, verify that a test lamp illuminates between the B+ circuit terminal L and ground.

• If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the TCM.

3. Connect a test lamp between the PCS1 control circuit terminal M and the B+ circuit terminal L.
4. Command the PC Solenoid 1 ON and OFF with a scan tool and verify the PC Sol. 1 Pressure Command parameter changes from 1600 kPa (232 psi) to 0 kPa (0 psi). The test lamp should turn ON and OFF when changing between the commanded states.

• If the test lamp is always ON, test the control circuit for a short to ground. If the circuit tests normal, replace the TCM.
• If the test lamp is always OFF, test the control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the TCM.

5. Ignition OFF, install the X175 harness connector.
6. Remove the transmission oil pan. Refer to Oil Pan Replacement (Allison - Automatic Transmission).
7. Disconnect the PCS1 solenoid connector.
8. Connect a test lamp between terminals 1 and 2 of the internal harness.
9. Ignition ON, engine OFF, command the PC Solenoid 1 ON and OFF with a scan tool and verify the PC Sol. 1 Pressure Command parameter changes from 1600 kPa (232 psi) to 0 kPa (0 psi). The test lamp should turn ON and OFF when changing between the commanded states.

• If not the expected results, replace the transmission internal wiring harness. Refer to Wiring Harness Replacement (Allison - Automatic Transmission).

10. If all circuits Test normal, test or replace the PCS1 solenoid.

Component Testing

Static Testing

Note: You must perform the Circuit/System Testing first.

1. Ignition OFF, remove the PCS1 solenoid from the valve body. Refer to Control Valve Solenoid Replacement (SS1, SS2, SS3, TCC, and MAIN MOD) (Control Valve Solenoid Replacement (SS1, SS2, SS3, TCC, and MAIN MOD))Control Valve Solenoid Replacement (PCS1 and PCS2) (Control Valve Solenoid Replacement (PCS1 and PCS2)).
2. Test for an open circuit between the B+ circuit terminal 1 of the PCS1 and the PCS1 solenoid metal case and between the control circuit terminal 2 and the PCS1 solenoid metal case.

• If not within the specified range, replace the PCS1 solenoid.

3. Test for resistance between the control circuit terminal 2 and the B+ circuit terminal 1 of the PCS1. Refer to Temperature Versus Resistance (Transmission Fluid Temperature Sensor) (Temperature Versus Resistance (Transmission Fluid Temperature Sensor))Temperature Versus Resistance (Speed Sensor) (Temperature Versus Resistance (Speed Sensor))Temperature Versus Resistance (Solenoid) (Temperature Versus Resistance (Solenoid)).

• If not within the specified range, replace the PCS1 solenoid.

Repair Instructions

Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.

* Wiring Harness Replacement (Allison - Automatic Transmission)
* Control Valve Solenoid Replacement (SS1, SS2, SS3, TCC, and MAIN MOD) (Control Valve Solenoid Replacement (SS1, SS2, SS3, TCC, and MAIN MOD))Control Valve Solenoid Replacement (PCS1 and PCS2) (Control Valve Solenoid Replacement (PCS1 and PCS2))
* Control Module References (Control Module References) for TCM replacement, setup, and programming

Repair Verification

If another DTC is present, refer to Diagnostic Trouble Code (DTC) List - Vehicle (Diagnostic Trouble Code (DTC) List - Vehicle) and perform the appropriate diagnostic procedure.

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