CIRCUIT DESCRIPTION:
The sensor reference voltage diagnostic checks the integrity of the 5 volt reference used to power all of the analog input sensors such as oil temperature, Throttle Position Sensor (TPS), and the 6-speed Three-Position interface circuits. DTC P0643 is set when a 5 volt reference circuit voltage is above a calibrated voltage for a calibrated time period.

ACTION TAKEN WHEN THE DTC SETS:
When DTC P0643 is active, the following conditions occur:
1. The CHECK TRANS light is illuminated.
2. DTC is stored in TCM history.
3. Additional DTCs active depending on 5V reference to function normally.

CONDITIONS FOR CLEARING DTC/CHECK TRANS LIGHT:
Use the diagnostic tool to clear the DTC from the TCM history. The TCM automatically clears the DTC from the TCM history if the vehicle completes forty warm-up cycles without failure.

DIAGNOSTIC AIDS:
DTC P0643 can be caused by:
1. Chassis harness wire short to battery.
2. Broken or defective connector assemblies allowing pushed back pins to short together.
3. Unlocked connectors, missing seal plugs allowing moisture in connectors.
4. Defective TCM.

NOTE: The OEM transmission warranty, or the extended coverage for parts and labor, does not cover the repair or replacement of OEM or bodybuilder-provided components or any external wire harnesses not provided by the OEM.

Before repairing or replacing these components or circuits that caused a transmission issue, always contact the vehicle OEM call center and/or the vehicle OEM or bodybuilder service representative to verify the warranty coverage and proper payment arrangements, arrange an alternate sublet or repair plan (if needed), and get troubleshooting assistance for the repair (such as vehicle schematics, DTC trees, parts assistance, etc).