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Allison - Automatic Transmission




DTC P0975-P0977

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 P0975
- Shift Solenoid (SS) 2 Control Circuit Open

DTC P0976
- Shift Solenoid (SS) 2 Control Circuit Low Voltage

DTC P0977
- Shift Solenoid (SS) 2 Control Circuit High Voltage

Diagnostic Fault Information





Typical Scan Tool Data





Circuit/System Description

Shift solenoid 2 (SS2) is a normally closed (N/C) solenoid that provides control main pressure to stroke shift valve 2. The transmission control module (TCM) determines the proper solenoid command logic to move shift valve 2 to attain a particular range. The TCM provides B+ to pressure control solenoid 2 (PCS2), and shift solenoids 1, 2, and 3 (SS1, SS2, and SS3) through a separate solid state device called high side driver 2 (HSD2). The TCM uses a low side driver to switch SS2 ON and OFF. Since the shift valve position is critical in determining the correct transmission range, a pressure switch located in the pressure switch manifold provides feedback to the TCM on the position of the valve.

Conditions for Running the DTC

P0975-P0977
* DTC P2669, P2670, or P2671 is not set.
* Battery voltage is between 9-18 V.
* Engine speed is greater than 200 RPM.

Conditions for Setting the DTC

P0975

The TCM detects an open circuit on the SS2 control circuit for 1 second.

P0976

The TCM detects a short to ground on the SS2 control circuit for 1 second.

P0977

The TCM detects a short to voltage on the SS2 circuit for 1 second.

Action Taken When the DTC Sets

P0975-P0977
* DTCs P0975, P0976, and P0977 are Type A DTCs.
* If the DTC sets while in a forward range, the TCM commands 1st, 3rd, or 5th gear. If the DTC sets while in REVERSE, the transmission stays in reverse.
* Main modulation (MAIN MOD) is inhibited.
* The TCM freezes shift adapts.
* The TCM inhibits torque converter clutch (TCC) engagement.

Conditions for Clearing the DTC

DTCs P0975, P0976, and P0977 are Type A DTCs.

Diagnostic Aids

P0975
* You may have to drive the vehicle in order to experience a condition.
* DTC P0975, set in combination with DTC P0964, P0975, or P0979, may indicate an open in the HSD2 circuit.

P0976 and P0977

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 Shift Solenoid 2 ON and OFF with a scan tool. Observe the scan tool Shift Solenoid 2 parameter. The Shift Solenoid 2 parameter should turn On and Off.
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 N 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 SS2 control circuit terminal B and the B+ circuit terminal N.
4. Command the Shift Solenoid 2 ON and OFF with a scan tool and verify the Shift Solenoid 2 parameter changes from On to Off. 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 SS2 solenoid connector.
8. Connect a test lamp between terminals A and B of the internal harness.
9. Ignition ON, engine OFF, command the Shift Solenoid 2 ON and OFF with a scan tool and verify the Shift Solenoid 2 parameter changes from On to Off. 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 SS2 solenoid.

Component Testing

Static Testing

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

1. Ignition OFF, remove the SS2 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 SS2 and the SS2 solenoid metal case and between the control circuit terminal B and the SS2 solenoid metal case.

• If not within the specified range, replace the SS2 solenoid.

3. Test for resistance between the B+ circuit terminal A and the control circuit terminal B. 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 SS2 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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