P0960
DTC P0960, P0962, or P0963
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 Descriptors
DTC P0960
- Main Modulation/Line Pressure Control (PC) Solenoid Control Circuit Open
DTC P0962
- Main Modulation/Line Pressure Control (PC) Solenoid Control Circuit Low Voltage
DTC P0963
- Main Modulation/Line Pressure Control (PC) Solenoid Control Circuit High Voltage
Diagnostic Fault Information
Circuit/System Description
Main Modulation/Line Pressure Control (MAIN MOD) Solenoid is a normally closed (N/C) solenoid that regulates transmission line pressure. This solenoid is used to reduce line pressure when the vehicle is not moving with engine at idle, thus decreasing engine load and also improving cooler flow. The transmission control module (TCM) commands the MAIN MOD solenoid ON when specific transmission and engine conditions are met. When the MAIN MOD solenoid is commanded ON, control main pressure is routed to the main regulator valve lowering the line pressure.
The TCM provides B+ to the MAIN MOD solenoid, torque converter clutch (TCC) pressure control solenoid, and pressure control solenoid 1 (PCS1) through a separate solid state device called high side driver 1 (HSD1). The TCM uses a low side driver to switch the MAIN MOD solenoid ON and OFF.
Conditions for Running the DTC
P0960 or P0962
* DTC P0657, P0658, or P0659 is not set.
* Battery voltage is between 9-18 V.
* Engine speed is greater than 200 RPM.
* HSD1 is enabled.
P0963
* DTC P0657, P0658, or P0659 is not set.
* Battery voltage is between 9-18 V.
* Engine speed is greater than 200 RPM.
* HSD1 is enabled.
Conditions for Setting the DTC
P0960
The TCM detects an open circuit on the MAIN MOD control circuit for 1 second.
P0962
The TCM detects a short to ground on the MAIN MOD control circuit for 1 second.
P0963
The TCM detects a short to voltage on the MAIN MOD circuit for 1 second.
Action Taken When the DTC Sets
P0960
* DTC P0960 is a Type A DTC.
* Main Modulation/Line Pressure Control is disabled.
P0962 or P0963
* DTCs P0962 and P0963 are Type A DTCs.
* Main Modulation/Line Pressure Control is disabled or the transmission will lock into range.
Conditions for Clearing the DTC
DTCs P0960, P0962, and P0963 are Type A DTCs.
Diagnostic Aids
P0960
* You may have to drive the vehicle in order to experience a condition.
* If DTC P0960 is accompanied by DTC P2727 and or DTC P2761, the open is most likely in the HSD1 circuit.
P0962 or P0963
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 Modulated Main Pres. Ctrl. Sol. ON and OFF with a scan tool. The Line PC Sol. Pressure Command parameter should change from 0 kPa (0 psi) to 1600 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 control circuit terminal S and the B+ circuit terminal L.
4. Command the Modulated Main Pres. Ctrl. Sol. ON and OFF with a scan tool and verify the Line PC Sol. Pressure Command parameter changes from 0 kPa (0 psi) to 1600 kPa (232 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 at the transmission.
6. Remove the transmission oil pan. Refer to Oil Pan Replacement (Allison - Automatic Transmission).
7. Disconnect the Modulated Main Pressure Control Solenoid Valve connector.
8. Connect a test lamp between the A and B terminals of the internal harness.
9. Ignition ON, engine OFF, Command the Modulated Main Pres. Ctrl. Sol. ON and OFF with a scan tool. 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 circuits test normal, test or replace the Main Mod solenoid.
Component Testing
Static Testing
Note: You must perform the Circuit/System Testing first.
1. Ignition OFF, remove the MAIN MOD 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 A of the MAIN MOD solenoid and the MAIN MOD solenoid metal case and between the control circuit terminal B and the MAIN MOD solenoid metal case.
• If not within the specified range, replace the MAIN MOD solenoid.
3. Test for resistance between the control circuit terminal B, and the B+ circuit terminal A of the MAIN MOD solenoid. 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 MAIN MOD 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.