P0721

P0721-OUTPUT SPEED SENSOR CIRCUIT PERFORMANCE

For a complete wiring diagram Refer to the Wiring Information.

Theory of Operation

The purpose of the monitoring is to detect rationality failures of the input speed and output speed sensor signals as well as the wheel speed and engine speed CAN signals. There are three categories of rationalities which include: Multi sensor comparisons of up to three signals (input, output and wheel speed). Monitoring of the gradient of the input speed signal. Double failure monitoring to determine unique failure situations which could require unique limp-in functionality.

- When Monitored:
Continuously when the ignition switch is turned to the run position, the engine is running and the vehicle is moving, with no electrical failures on the Input Speed, Output Speed or Wheel Speed Sensors.

- Set Condition:
The failure is detected if the difference between the output speed measured by the TCM and the following signals are both greater than a threshold for a calibrated amount of time. When the calculated output speed from the wheel speed signal from CAN or the calculated output speed from the output speed measured by the TCM.





Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. 8HP45 Pre-Diagnostic Troubleshooting Procedure

1. CHECK DTC IS CURRENT
1. Turn the ignition ON.
2. With the scan tool, CLEAR transmission DTCs.
3. Raise the vehicle on the hoist.
4. Start the engine.
5. With the scan tool, monitor the Output Speed Sensor RPM.
6. Firmly apply the brake pedal and place the gear selector in Drive.

WARNING: To avoid personal injury or death, keep hands and feet clear of rotating wheels.

7. Release the brakes and raise the engine rpm to allow the transmission to perform a 2-3 and 3-4 upshift.

Did the Output Speed Sensor display an rpm above 1,000?

Yes

- Go To 2

No

- Using the schematics as a guide, check the Transmission Control Module Assembly (TCMA) terminals for corrosion, damage or terminal push out. Pay particular attention to all power and ground circuits. If no problems are found, replace and program the TCMA. Valve Body - Removal.
- Perform the TRANSMISSION VERIFICATION TEST. Verification Tests.

2. INTERNAL TRANSMISSION
1. This DTC is an indication of a internal transmission failure.
2. Remove the Transmission Oil Pan and inspect for excessive debris such as clutch friction material or metal contamination.

Is there any indication of an internal transmission failure?

Yes

- Repair internal transmission as necessary.
- Perform the TRANSMISSION VERIFICATION TEST. Verification Tests.

No

- Using the schematics as a guide, check the TCMA terminals for corrosion, damage or terminal push out. Pay particular attention to all power and ground circuits. If no problems are found, replace and program the TCM. Valve Body - Removal.
- Perform the TRANSMISSION VERIFICATION TEST. Verification Tests.