Diagnostic Instructions
| • | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. |
| • | Review Strategy Based Diagnosis for an overview of the diagnostic approach. |
| • | Diagnostic Procedure Instructions provides an overview of each diagnostic category. |
DTC Descriptors
DTC P0721: Output Speed Sensor PerformanceDTC P0722: Output Speed Sensor Circuit Low Voltage
DTC P0723: Output Speed Sensor Circuit Intermittent
Diagnostic Fault Information
Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
|---|---|---|---|---|
OSS Supply Voltage | P0722, P0723 | P0722, P0723 | P0722, P0723 | P0723 |
Low Reference | P0722, P0723 | P0722, P0723 | P0722, P0723 | P0723 |
Typical Scan Tool Data
Circuit | Normal Range | Open/High Resistance | Short to Voltage | Short to Ground |
|---|---|---|---|---|
Operating Conditions: Vehicle moving, normal operating temperature | ||||
OSS Signal | Forward/Reverse | Invalid/Unknown | Invalid/Unknown | Invalid/Unknown |
OSS Supply Voltage | Forward/Reverse | Invalid/Unknown | Invalid/Unknown | Invalid/Unknown |
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, 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.
Reference Information
Schematic Reference
Automatic Transmission Controls Schematics
Connector End View Reference
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
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
- Disconnect the OSS connector.
- Test for 8.3-9.3 volts between the OSS supply voltage circuit and ground.
- 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.
- Set the J 38522 Signal to 8 volts, the Frequency to 120 and the Percent Duty Cycle to 50.
- With the ignition ON, observe the Transmission OSS parameter, The Transmission OSS parameter should display between 100-400 RPM.
| ⇒ | 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. |
| ⇒ | 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, visually inspect the OSS and the output shaft machined surface for damage or misalignment. If OK, replace the OSS. |
Component Testing
Perform the Control Solenoid Valve and Transmission Control Module Assembly Output Shaft Speed Input Test.
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
- Perform the Automatic Transmission Wiring Harness and Output Speed Sensor Removal and Automatic Transmission Wiring Harness and Output Speed Sensor Installation for OSS replacement.
- Perform Control Module References for control solenoid (w/body and TCM) valve assembly replacement, setup, and programming.
- Perform the Control Solenoid Valve and Transmission Control Module Assembly Inspection.
- Perform the Control Solenoid Valve and Transmission Control Module Assembly Output Shaft Speed Input Test.
