Transmission Control Module (TCM) - NAG1

P0643-SENSOR REFERENCE VOLTAGE 1 CIRCUIT HIGH





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

Theory of Operation

The Sensor Supply Voltage circuit supplies a 6 volt power supply for the two input speed sensors. The Sensor Supply Voltage circuit is constantly monitored for correct voltage between 4.8 to 7.2 volts. If the voltage does not stay within the 4.8 to 7.2 volt range, the appropriate DTC will set.

- When Monitored:
Continuously with the ignition on and no overvoltage condition exist.

- Set Condition:
When the monitored sensor voltage is not within specified limits and rises above 7.2 volts.





Always perform the NAG1 Pre-Diagnostic Troubleshooting procedure before proceeding. NAG1 Pre-Diagnostic Troubleshooting Procedure.

1. CHECK FOR SPEED SENSOR DTCS
1. With the scan tool, check for other transmission DTCs.

Are there any speed sensor and/or temperature sensor DTCs present?

Yes

- Perform the appropriate diagnostic procedure.

No

- Go To 2

2. CHECK SOLENOID SUPPLY VOLTAGE ON THE SCAN TOOL
1. Start the engine.
2. With the scan tool, check the Transmission Solenoid Supply Voltage.

Is the Transmission Solenoid Supply Voltage above 7.2 volts?

Yes

- Go To 3

No

- Go To 5

3. CHECK (T72) SENSOR SUPPLY CIRCUIT VOLTAGE




1. While back probing, measure the voltage of the (T72) Solenoid Supply Voltage circuit in the TCM harness connector.

Does the measured voltage match the voltage reading on the scan tool ± 0.2 volts?

Yes

- Go To 4

No

- Using the schematics as a guide, check the Transmission Control Module (TCM) terminals for corrosion, damage, or terminal push out. Pay particular attention to all power and ground circuits. If no problems are found, replace the TCM. Transmission Control Module - Description
- Perform NAG1 TRANSMISSION VERIFICATION TEST. NAG1 Transmission Verification Test.

4. (T72) SENSOR SUPPLY VOLTAGE CIRCUIT SHORT TO ANOTHER CIRCUIT




1. Turn the ignition off to the lock position.
2. Disconnect the Transmission Electrohydraulic Control Unit Assembly harness connector.
3. Disconnect all TCM harness connectors.
4. Measure the resistance between the (T72) Solenoid Supply Voltage circuit and all other circuits in the Transmission Electrohydraulic Control Unit harness connector.

Is the resistance below 5.0 ohms between the (T72) Solenoid Supply Voltage circuit and all other circuits in the Transmission Electrohydraulic Control Unit Assembly harness connector?

Yes

- Repair the (T72) Solenoid Supply Voltage circuit for a short to another circuit(s).
- Perform NAG1 TRANSMISSION VERIFICATION TEST. NAG1 Transmission Verification Test.

No

- Using the schematics as a guide, check the Transmission Control Module (TCM) terminals for corrosion, damage, or terminal push out. Pay particular attention to all power and ground circuits. If no problems are found, replace the TCM. Transmission Control Module - Description
- Perform NAG1 TRANSMISSION VERIFICATION TEST. NAG1 Transmission Verification Test.

5. CHECK THE 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.

Were there any problems found?

Yes

- Repair as necessary.
- Perform NAG1 TRANSMISSION VERIFICATION TEST. NAG1 Transmission Verification Test.

No

- Test Complete.