P077B
DTC P077B
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle (Initial Inspection and Diagnostic Overview) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Initial Inspection and Diagnostic Overview) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Initial Inspection and Diagnostic Overview) provides an overview of each diagnostic category.
DTC Descriptor
DTC P077B
- Output Speed Sensor Direction Incorrect
Diagnostic Fault Information
Typical Scan Tool Data
Circuit/System Description
The output speed sensor (OSS) assembly has 2 internal hall-effect type sensors, and is capable of sensing both speed and direction. The OSS mounts to the A/Trans case assembly and is connected to the control solenoid (w/body and TCM) valve assembly through a wire harness and connector. The sensor faces the front differential drive pinion (w/transfer gear) gear assembly machined teeth surface. The sensor receives 8.3-9.3 volts on the OSS supply voltage circuit from the transmission control module (TCM). As the output shaft rotates, the sensor produces a signal frequency based on the machined surface of the output shaft.
The two sensor elements in the OSS assembly are spaced approximately 1/2 a tooth apart.
* When the vehicle is moving in a forward direction, sensor A detects a particular tooth before sensor B.
* When the vehicle is moving in a reverse direction, sensor B detects a particular tooth before sensor A.
The electronics in the sensor combine the two signals and send a signal with a different pulse width. This signal is interpreted by the TCM for speed and direction and is transmitted through the GMLAN circuits to the engine control module (ECM) and the hybrid powertrain control module (HPCM). The ECM, HPCM, and TCM compare the OSS signal with the ABS wheel speed sensor signal.
Conditions for Running the DTC
* The OSS is less than 50 RPM.
* The drive motor estimated output speed is greater than 50 RPM.
* DTC P215C is not set.
Conditions for Setting the DTC
The HPCM or the TCM detects an incorrect OSS direction.
Action Taken When the DTC Sets
HPCM
The HPCM calculates OSS direction based on drive motor 1 and drive motor 2 direction.
TCM
* The TCM freezes transmission adaptive functions.
* The TCM turns OFF all solenoids.
Conditions for Clearing the DTC
HPCM
P077B is a Type A DTC.
TCM
P077B is a Type A DTC.
Diagnostic Aids
Inspect the OSS, harness, connector and control solenoid (w/body and TCM) valve assembly pins for metallic debris. Proper torque of the OSS mounting bolt is critical to proper OSS operation. Use a terminal test kit for any test that requires probing the control solenoid (w/body and TCM) valve assembly harness connector or a component harness connector.
Reference Information
Schematic Reference
Automatic Transmission Controls Schematics (Electrical Diagrams)
Connector End View Reference
Component Connector End Views (Connector Views)
Electrical Information Reference
* Circuit Testing (Component Tests and General Diagnostics)
* Connector Repairs (Component Tests and General Diagnostics)
* Testing for Intermittent Conditions and Poor Connections (Component Tests and General Diagnostics)
* Wiring Repairs (Component Tests and General Diagnostics)
DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions (Diagnostic Trouble Code Descriptions)
Scan Tool Reference
Control Module References (Programming and Relearning) for scan tool information.
Special Tools
J 38522 - Variable Signal Generator
Circuit/System Verification
1. Verify that DTCs P0721, P0722, P0723, P0966, P0967, P0969, P0970, P0971, P0973, P0974, P0976, P0977, P2720, P2721, P2728, P2729, or P2730 are not set.
• If any of the DTCs are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle (Diagnostic Trouble Code Descriptions).
2. Operate the vehicle at 16-32 km/h (10-20 mph) while observing the Transmission Data Output Shaft Direction parameter on the scan tool.
• The Output Shaft Direction parameter should match vehicle direction.
Circuit/System Testing
1. Ignition OFF, remove the control valve body cover. Refer to Control Valve Lower Body and Upper Body Replacement (2MT70 - Automatic Transmission).
2. Connect the TCM harness connector.
3. Disconnect the output speed sensor (OSS) harness connector from the control solenoid (w/body and TCM) valve assembly.
4. Connect the J 38522 - variable signal generator between the supply voltage terminal B and OSS signal terminal A at the control solenoid (w/body and TCM) valve assembly. Refer to Control Solenoid Valve and Transmission Control Module Assembly Output Shaft Speed Input Test (Control Solenoid Valve and Transmission Control Module Assembly Output Shaft Speed Input Test) for further instructions.
5. Set the J 38522 - variable signal generator signal to 8 volts, the frequency to 120 and the percent duty cycle to 50.
6. Ignition ON, observe the scan tool Transmission OSS parameter. The scan tool Transmission OSS parameter should be between 100-400 RPM.
• If not the specified value, replace the control solenoid (w/body and TCM) valve assembly.
7. Test the output speed sensor harness for an open, short to ground or short to voltage.
• If all circuits test normal, test or replace the output speed sensor.
Component Testing
Perform the Control Solenoid Valve and Transmission Control Module Assembly Output Shaft Speed Input Test (Control Solenoid Valve and Transmission Control Module Assembly Output Shaft Speed Input Test).
Repair Instructions
Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.
* Perform the Automatic Transmission Wiring Harness and Output Speed Sensor Removal (Overhaul) and Automatic Transmission Wiring Harness and Output Speed Sensor Installation (Overhaul) for OSS replacement.
* Control Module References (Programming and Relearning) for control solenoid (w/body and TCM) valve assembly replacement, setup, and programming.
* Control Solenoid Valve and Transmission Control Module Assembly Inspection (Control Solenoid Valve and Transmission Control Module Assembly Inspection).
* Control Solenoid Valve and Transmission Control Module Assembly Output Shaft Speed Input Test (Control Solenoid Valve and Transmission Control Module Assembly Output Shaft Speed Input Test).
* Transmission Replacement (Removal and Replacement) for transmission removal.