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P0721






P0721-OUTPUT SPEED SENSOR CIRCUIT PERFORMANCE

Special Tools:






For a complete wiring diagram, refer to the Wiring Information.

Theory of Operation

1.
- When in gear, if the gear ratio does not compare to a known gear ratio, the corresponding in-gear DTCs P0731-36 and P1736 are set.
- An excessive change in input or output speeds indicating an intermittent signal results in DTCs P0716 and/or P0721 being set.
- If the common speed sensor ground circuit is lost, both sensor inputs will read the signal from the input speed sensor at idle in neutral. Since the input speed sensor has 60 teeth and the output speed sensor has 30 teeth, this results in a an apparent speed ratio of 1:2 and may cause DTC P1794 to set.

- When Monitored:
The transmission gear ratio is monitored continuously while the transmission is in gear.

- Set Condition:
If there is an excessive change in output RPM in any gear. This DTC can take up to five minutes of problem identification before illuminating the MIL.





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

1. CHECK IF THE DTC IS CURRENT
1. Turn the ignition OFF to the LOCK position.

CAUTION: Properly support the vehicle and raise all drive wheels off the ground.

2. Release the parking brake.
3. Start the engine in park.
4. Place the transmission gear selector in drive, release foot from brake.

WARNING: Be sure to keep hands and feet clear of rotating wheels.

5. With the scan tool, monitor the Output Speed Sensor RPM.

Is the Output Speed Sensor RPM below 100 RPM?

Yes

- Go To 2

No

- Go To 9

2. CHECK THE OUTPUT SPEED SENSOR
1. Turn the ignition OFF to the LOCK position.
2. Remove the Starter Relay.

CAUTION: Removal of the Starter Relay will prevent the vehicle from being started in gear.

WARNING: The Starter Relay must be removed from the PDC. Failure to do so may result in possible serious or fatal injury.

NOTE: Failure to remove the Starter Relay can cause a Transmission - No Response condition.

3. Install the (8333A).
4. Ignition ON, Engine Not Running.
5. With the Transmission Simulator, set the selector switch to 3000/1000 and the Input/Output switch to ON.
6. With the scan tool, monitor the Input and Output Speed Sensor RPM.

Does the Input Speed read 3000 RPM and the Output Speed read 1000 RPM (± 50 RPM)?

Yes

- Replace the Output Speed Sensor. Output Speed Sensor - Removal.
- Perform the 65RFE TRANSMISSION VERIFICATION TEST. 65RFE Transmission Verification Test.

No

- Go To 3

3. CHECK THE (T14) OUTPUT SPEED SIGNAL CIRCUIT FOR AN OPEN




1. Turn the ignition OFF to the LOCK position.
2. Disconnect the (8333A).
3. Disconnect the PCM harness connectors and connect the (8815A).

CAUTION: Do not probe the PCM harness connectors. Probing the PCM harness connectors will damage the PCM terminals resulting in poor terminal to pin connection. Install the (8815A) to perform diagnosis.

4. Measure the resistance of the (T14) Output Speed Signal circuit from the Output Speed Sensor harness connector to the appropriate terminal of the (8815A).

Is the resistance above 5.0 ohms?

Yes

- Repair the (T14) Output Speed Signal circuit for an open.
- Perform the 65RFE TRANSMISSION VERIFICATION TEST. 65RFE Transmission Verification Test.

No

- Go To 4

4. CHECK THE (T13) SENSOR GROUND CIRCUIT FOR AN OPEN




1. Measure the resistance of the (T13) Sensor Ground circuit between the Output Speed Sensor harness connector and the appropriate terminal of the (8815A).

Is the resistance above 5.0 ohms?

Yes

- Repair the (T13) Sensor Ground circuit for an open.
- Perform the 65RFE TRANSMISSION VERIFICATION TEST. 65RFE Transmission Verification Test.

No

- Go To 5

5. CHECK THE (T14) OUTPUT SPEED SIGNAL CIRCUIT FOR A SHORT TO GROUND




1. Measure the resistance between ground and the (T14) Output Speed Signal circuit.

Is the resistance below 5.0 ohms?

Yes

- Repair the (T14) Output Speed Signal circuit for a short to ground.
- Perform the 65RFE TRANSMISSION VERIFICATION TEST. 65RFE Transmission Verification Test.

No

- Go To 6

6. CHECK THE (T13) SENSOR GROUND CIRCUIT FOR A SHORT TO GROUND




1. Measure the resistance between ground and the (T13) Sensor Ground circuit.

Is the resistance below 5.0 ohms?

Yes

- Repair the (T13) Sensor Ground circuit for a short to ground.
- Perform the 65RFE TRANSMISSION VERIFICATION TEST. 65RFE Transmission Verification Test.

No

- Go To 7

7. CHECK THE (T14) OUTPUT SPEED SIGNAL CIRCUIT FOR A SHORT TO VOLTAGE




1. Remove the Transmission Control Relay.
2. Place a jumper wire between the Fused B(+) circuit and the Transmission Relay Output circuit in the Transmission Control Relay connector.
3. Ignition ON, Engine Not Running.
4. Measure the voltage of the (T14) Output Speed Signal circuit.

Is the voltage above 0.5 volts?

Yes

- Repair the (T14) Output Speed Signal circuit for a short to voltage.
- Perform the 65RFE TRANSMISSION VERIFICATION TEST. 65RFE Transmission Verification Test.

No

- Go To 8

8. CHECK THE (T13) SENSOR GROUND CIRCUIT FOR A SHORT TO VOLTAGE




1. Measure the voltage of the (T13) Sensor Ground circuit.

Is the voltage above 0.5 volts?

Yes

- Repair the (T13) Sensor Ground circuit for a short to voltage.
- Perform the 65RFE TRANSMISSION VERIFICATION TEST. 65RFE Transmission Verification Test.

No

- Using the schematics as a guide, check the Powertrain Control Module (PCM) 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 PCM. With the scan tool, perform a Quick Learn. Powertrain Control Module - Removal.
- Perform the 65RFE TRANSMISSION VERIFICATION TEST. 65RFE Transmission Verification Test.

9. CHECK WIRING AND CONNECTORS
1. The conditions necessary to set this DTC are not present at this time.
2. Using the schematics as a guide, inspect the wiring and connectors specific to this circuit.
3. Wiggle the wires while checking for shorted and open circuits.
4. With the scan tool, check the Event Data to help identify the conditions in which the DTC set.

Were any problems found?

Yes

- Repair as necessary.
- Perform the 65RFE TRANSMISSION VERIFICATION TEST. 65RFE Transmission Verification Test.

No

- Test Complete.

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