P0643

DTC P0643

Circuit Description
The engine control module (ECM) provides 5 volts reference voltage through the reference circuit 1 to the following sensors:
- Accelerator pedal position (APP) sensor 1
- PTO accelerator sensor
- Idle up volume
- Boost pressure sensor
- Fuel rail pressure sensor
- EGR valve position sensor

The 5 volts reference circuits are independent of each other outside the ECM, but are bussed together inside the ECM. Therefore, a short circuit condition on one sensor 5 volts reference circuit may affect the entire sensor 5 volt reference circuit 1. The ECM monitors the voltage on the 5 volts reference circuit 1. If the ECM detects the voltage is excessively high, this DTC will set.

Condition for Running the DTC
- The battery voltage is between 10-16 volts.
- The ignition switch is ON.

Condition for Setting the DTC
- The ECM detests that the 5 volts reference circuit 1 voltage is more than 5.5 volts.

Action Taken When the DTC Sets
- The ECM illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails.
- The ECM records the operating conditions at the time the diagnostic fails. The ECM stores this information in the Failure Records.
- The ECM limits fuel rail pressure within 11600 psi (80 MPa).
- The ECM limits accelerator control range within 40%.
- The ECM closes the EGR valve and holds to close position.
- The ECM inhibits the cruise control.
- The ECM inhibits the PTO control.

Condition for Clearing the DTC
- A current DTC clears when the ignition is turned OFF.
- Clear the MIL and the DTC with a scan tool.

Diagnostic Aids
If an intermittent condition is suspected, the following may cause an intermittent:
- Misrouted harness.
- Rubbed through wire insulation.

Check for the following conditions:
- Damaged harness: Inspect the wiring harness for damage. If the harness appears to be OK, observe the "DTC P0643" display on the scan tool with ignition ON, engine OFF while moving connectors and wiring harness related to the sensor. A change in the display will indicate the location of the fault.

DTC P0643

Schematic Reference: Engine Controls Schematics

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