Automatic Transmission - 2MT70
DTC P0721-P0723
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 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/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
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.
* The transmission output speed is 1,000 RPM or greater for 1 second.
* Output speed has not increased greater than 500 RPM in 25 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 drops 1,000 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
* P0721 and P0723 are a Type A DTC.
* P0722 is a Type B 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
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. 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.
1. 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.
2. Perform 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 Transmission Control Module Assembly Inspection).
4. 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).