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P0721




DTC P0721-P0723

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (with HP2) (Initial Inspection and Diagnostic Overview)Diagnostic System Check - Vehicle (without HP2) (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 Descriptors
DTC P0721
- Output Speed Sensor Performance

DTC P0722
- Output Speed Sensor Circuit Low Voltage

DTC P0723
- Output Speed Sensor Circuit Intermittent

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/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.

* 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

P0721

The ignition is ON.

P0722
* No OSS DTCs P0721 or P0723.
* The selected range is not PARK or NEUTRAL.
* The vehicle speed is greater than 16 km/h (10 mph).

P0723
* No OSS DTCs P0721 or P0722.
* The engine run time is greater than 6 seconds.

Conditions for Setting the DTC

P0721

The TCM detects an invalid OSS direction.

P0722
* The TCM detects no signal from the OSS.
* The transmission output speed is less than 50 RPM for 1.5 seconds.

P0723
* The TCM detects an unrealistic signal drop from the OSS.
* OSS DTC P0723 has not failed this ignition.
* The transmission output speed is 1,000 RPM or greater for 6 seconds.
* The transmission output speed drops 1,300 RPM for greater than 4 seconds and does not recover.

Action Taken When the DTC Sets

P0721

The TCM calculates vehicle direction.

P0722 and P0723

The TCM calculates vehicle speed based on the wheel speed sensors.

Conditions for Clearing the DTC

* P0723 is a Type A DTC.
* P0721 and P0722 are a Type B DTC.

Diagnostic Aids

Inspect the OSS, harness, and connector pins for metallic debris and the hybrid direct, 2-3-4 clutch housing assembly machined teeth for damage or misalignment. Even one bent or misaligned tooth, and or contact with the OSS, may cause this DTC to set. Proper torque of 9-13 Nm(80-115 lb in) to the OSS mounting bolt is critical to proper OSS operation. The hybrid system is very sensitive to the OSS signal for overall operation.

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

Operate the vehicle at 16-32 km/h (10-20 mph) while observing the Transmission OSS and OSS Supply Voltage parameters on the scan tool.

The Transmission OSS should vary with the vehicle speed and not drop out.
The OSS Supply Voltage should display OK.

Circuit/System Testing

1. Remove the OSS. Inspect the OSS, harness, and connector pins for metallic debris and the hybrid direct, 2-3-4 clutch housing assembly machined teeth for damage or misalignment. Even one bent or misaligned tooth, and or contact with the OSS, may cause this DTC to set. Proper torque of 9-13 Nm(80-115 lb in) to the OSS mounting bolt is critical to proper OSS operation. The hybrid system is very sensitive to the OSS signal for overall operation.

• If damage is observed, replace the damaged component.

2. 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 the OSS supply voltage circuit tests normal, replace the control solenoid (w/body and TCM) valve assembly.
• If greater than 9.3 volts, test the OSS supply voltage circuit for a short to voltage.

3. Using a terminal test kit, connect the red lead of J 38522 to the OSS signal circuit terminal B and the black lead to the OSS supply voltage circuit terminal A.
4. Set the J 38522 Signal to 8 volts, the Frequency to 120 and the Percent Duty Cycle to 50.
5. With the ignition ON, observe the Transmission OSS parameter, The Transmission OSS parameter should display between 100-400 RPM.

• If the Transmission OSS is not within the specified range, test the Transmission 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 Transmission OSS is within the specified range, replace the OSS.

Component Testing

Perform the Control Solenoid Valve and Transmission Control Module Assembly Output Shaft Speed Input Test (Control Solenoid Valve and TCM Assembly Solenoid Performance Test).

Repair Instructions

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

1. Perform the Output Speed Sensor Replacement (Service and Repair).
2. Control Module References (Programming and Relearning) for control solenoid (w/body and TCM) valve assembly replacement, setup, and programming.
3. Perform the Control Solenoid Valve and Transmission Control Module Assembly Inspection (Control Solenoid Valve and TCM Assembly Solenoid Performance Test).
4. Perform the Control Solenoid Valve and Transmission Control Module Assembly Output Shaft Speed Input Test (Control Solenoid Valve and TCM Assembly Solenoid Performance Test).

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