Allison - Automatic Transmission

DTC P2723 or P2724

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 P2723
- Pressure Control (PC) Solenoid 1 Stuck Off

DTC P2724
- Pressure Control (PC) Solenoid 1 Stuck On

Circuit/System Description

The transmission has 2 pressure control solenoids that controls the flow of transmission fluid to engage clutches. The flow is directed through shift valves that allows the fluid pressure to engage different clutches. The vehicle speed sensor and automatic transmission turbine speed sensor contains a permanent magnet surrounded by a coil that gives off a continuous magnetic field. As the vehicle is driven, a speed sensor rotor located near the magnetic pickup of the speed sensor coil also rotates. This rotation produces a variable voltage signal that is proportional to the transmission turbine and output speed. The TCM uses the signals to calculate the gear ratio. The TCM compares the computed ratio to the commanded gear ratio.

Conditions for Running the DTC

P2723
* Engine speed is greater than 200 RPM.
* Output speed is 125 RPM or greater.
* Turbine speed is 60 RPM or greater.
* The transmission fluid temperature is greater than -25°C (-13°F).
* DTC P0716, P0717, P0721, P0722, P0877, or P0878 is not set.

P2724
* Engine speed is greater than 200 RPM.
* Output speed is 200 RPM or greater.
* Turbine speed is 200 RPM or greater.
* The transmission fluid temperature is greater than -25°C (-13°F).
* DTC P0716, P0717, P0721, P0722, P0877, or P0878 is not set.

Conditions for Setting the DTC

P2723

During a shift with PCS1 controlling the oncoming clutch, the TCM detects that the calculated commanded gear ratio differs from the known commanded gear ratio for 2 seconds.

P2724

During a shift with PCS1 controlling the off going clutch, the TCM detects that the off going gear ratio remains the same even though it is commanded off for 1 second.

Action Taken When the DTC Sets

P2723 or P2724
* DTCs P2723 and P2724 are Type A DTCs.
* If the DTC sets with the transmission in a forward gear, the TCM commands the previous gear. If the transmission was in reverse or neutral, the TCM commands neutral.
* The TCM inhibits torque converter clutch (TCC) engagement.

Conditions for Clearing the DTC

DTCs P2723 and P2724 are Type A DTCs.

Diagnostic Aids

* You must drive the vehicle in order to experience a condition.
* DTCs P2723 or P2724 may indicate a component condition with piston seals, clutch plates, or solenoids.
* DTCs P2723 or P2724 may be caused by a faulty speed sensor signal.

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. Perform the Transmission Fluid Level and Condition Check (Transmission Fluid Level and Condition Check) to verify correct fluid level and condition.
2. Perform a Road Test (Allison - Automatic Transmission) while observing the Turbine Speed and Transmission OSS parameters with a scan tool. The Turbine Speed and Transmission OSS parameters should increase and decrease steadily as the speed of the vehicle changes in each gear. The Turbine Speed will make a large change while the transmission is changing gears.
3. 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

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

1. Perform a line pressure test. Refer to Line Pressure Check (Line Pressure Check).

• If line pressure is low in all ranges, refer to Low Main Line Pressure in All Ranges (Low Main Line Pressure in All Ranges).
• If line pressure is low in a specific range or ranges, refer to Low Main Line Pressure in Specific Ranges, Normal Pressure in Other Ranges (Low Main Line Pressure in Specific Ranges, Normal Pressure in Other Ranges).

Warning

Chock the wheels to prevent the vehicle from moving. Failure to chock the wheels can cause personal injury when the electrical system is repaired.

2. Perform the clutch test. Refer to Clutch Test (Clutch Test).

• If not the specified value, refer to Excessive Slippage and Clutch Chatter (Excessive Slippage and Clutch Chatter).

3. If the above tested normal, refer to Functional Test (Functional Test).

Repair Instructions

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

* Speed Sensor 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 Valve Body Cleaning and Inspection (84. Control Valve Body Cleaning and Inspection)

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.