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/T rear 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 hybrid direct, 2-3-4 clutch housing 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.

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. The HPCM also compares the output shaft direction with the drive motor 1 and drive motor 2 direction.

The HPCM or the TCM detects an incorrect OSS direction.

HPCM

The HPCM calculates OSS direction based on drive motor 1 and drive motor 2 direction.

TCM

HPCM

P077B is a Type A DTC.

TCM

P077B is a Type A DTC.

Inspect the OSS, harness, connector and control solenoid (w/body and TCM) valve assembly pins for metallic debris and output shaft machined face for damage or misalignment. 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.

Schematic Reference

Automatic Transmission Controls Schematics

Connector End View Reference

Component Connector End Views

Electrical Information Reference

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information.

Special Tools

J 38522 Variable Signal Generator

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.

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.

1. Operate the vehicle at 16-32 km/h (10-20 mph) while observing the Transmission Data Output Shaft Direction parameter on the scan tool.

⇒	If the Output Shaft Direction parameter corresponds with the vehicle direction and DTC P077B is set in the HPCM and not the TCM, replace the HPCM.

⇒	If DTC P077B is also set in the TCM continue testing.

2. Disconnect the OSS connector.
3. Test for 8.3-9.3 volts between the OSS supply voltage circuit and ground.

⇒	If less than 8.3 volts, test the OSS supply voltage circuit for an open/high resistance or short to ground.

⇒	If greater than 9.3 volts, test the OSS supply voltage circuit for a short to voltage.

4. Perform the Control Solenoid Valve and Transmission Control Module Assembly Output Shaft Speed Input Test.

⇒	If the OSS signal is not within the specified range, test the OSS signal circuit for an open/high resistance, short to ground, or a short to voltage.

⇒	If the circuit tests normal, replace the control solenoid (w/body and TCM) valve assembly.

⇒	If the OSS signal is within the specified range, visually inspect the OSS and the output shaft machined surface for damage or misalignment. If OK, replace the OSS.

Perform the Control Solenoid Valve and Transmission Control Module Assembly Output Shaft Speed Input Test.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.