Transmission Control Module (TCM) - 8HP45

P0642-SENSOR REFERENCE VOLTAGE 1 CIRCUIT LOW

For a complete wiring diagram Refer to the Wiring Information.

Theory of Operation

The purpose of the monitoring is to detect circuit failures on the sensor supply voltage. This monitoring is done by observing the sensor supply voltage and the actual supply voltage of the Transmission Control Module (TCM) which is used for the circuit monitoring of the internal speed sensors. The TCM supplies the sensor supply voltage. These voltage levels are compared to predefined ranges that indicate short to battery, short to ground or open circuit.

- When Monitored:
Ignition on.

Supply voltage of the TCM is greater than a calibrated threshold.

- Set Condition:
A failure is detected if one of the following conditions occurs: Sensor supply voltage is lower than a calibrated threshold for an amount of time or the TCM detects an open circuit or short to ground at the input and output speed sensor at the same time.





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

1. CHECK IF DTC IS CURRENT

NOTE: The Transmission Control Module stores under Environmental Data the transmission operating conditions when the DTC was set. Before erasing any DTCs, record all information pertaining to the DTC.

1. With the scan tool, erase transmission DTCs.
2. Using the Environmental Data previously recorded, drive the vehicle and try to duplicate the condition in which the DTC set.

Does the DTC reset?

Yes

- Go To 2

No

- Go To 3

2. TRANSMISSION CONTROL MODULE ASSEMBLY (TCMA)

If there are no possible causes remaining, view repair.

Repair

- Using the schematics as a guide, check the TCMA terminals for corrosion, damage or terminal push out. Pay particular attention to power and ground circuits. Check Service Information Tune-ups or Service Bulletins for possible causes that may apply. Remove the transmission oil pan and the TCMA. Valve Body - Removal. Inspect and clean the solenoid terminals at the wiring harness leadframe for metallic contamination. Reinstall the TCMA. Valve Body - Installation. Connect the scan tool and erase the DTCs. Road test the vehicle and check for DTCs. If the DTC returns, replace and program the TCMA. Valve Body - Removal.
- Perform the TRANSMISSION VERIFICATION TEST. Verification Tests.

3. INTERMITTENT 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 wiring and connectors while checking for any possible open or shorted circuits.
4. Check for any Service Information Tune-ups or Technical Service Bulletins that may apply.

Were any problems found?

Yes

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

No

- Test Complete.