P0643
DTC P0642 or P0643
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle (Diagnostic System Check - Vehicle) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Strategy Based Diagnosis) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Diagnostic Procedure Instructions) provides an overview of each diagnostic category.
DTC Descriptors
DTC P0642
- 5-Volt Reference 1 Circuit Low Voltage
DTC P0643
- 5-Volt Reference 1 Circuit High Voltage
Diagnostic Fault Information
Circuit/System Description
The engine control module (ECM) supplies 5 volts to components through 5-volt reference circuits. These 5-volt reference circuits are independent of each other outside the ECM, but are bussed together in three reference groups inside the ECM. Therefore, a circuit condition on one sensor 5-volt reference circuit may affect multiple components. The ECM monitors voltage on the 5-volt reference circuits.
Conditions for Running the DTC
* The ignition is ON.
* The diagnostics run continuously.
Conditions for Setting the DTC
P0642
* The ECM detects the 5-volt reference 1 circuit voltage is less than 4.7 volts.
* The above condition is present for 2 seconds.
P0643
* The ECM detects the 5-volt reference 1 circuit voltage is more than 5.2 volts.
* The above condition is present for 2 seconds.
Action Taken When the DTC Sets
DTCs P0642 and P0643 are Type A DTCs.
Conditions for Clearing the MIL/DTC
DTCs P0642 and P0643 are Type A DTCs.
Reference Information
Schematic Reference
Engine Controls Schematics ([1][2]Electrical Diagrams)
Connector End View Reference
Component Connector End Views (Connector End Views By Name)
Electrical Information Reference
* Circuit Testing (Circuit Testing)
* Connector Repairs (Connector Repairs)
* Testing for Intermittent Conditions and Poor Connections (Testing for Intermittent Conditions and Poor Connections)
* Wiring Repairs (Wiring Repairs)
Scan Tool Reference
Control Module References (Programming and Relearning) for scan tool information
Circuit/System Verification
1. The engine starts and runs.
2. Observe the 5-Volt Reference 1 Circuit Status parameter with a scan tool. The parameter should display OK.
3. Engine running, observe the DTC information with a scan tool. DTCs P0642 or P0643 should not set.
4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.
Circuit/System Testing
Important: Additional DTCs will set when disconnecting the components.
1. Ignition OFF, disconnect the harness connector of all appropriate sensors for the applicable DTC.
Important: A short to voltage on the signal circuit of certain components may cause this DTC to set.
2. Ignition ON, measure for 4.8-5.2 volts between one of the 5-volt reference circuits and ground.
• If the voltage is less than the specified range, test for a short to ground on all the 5-volt reference circuits. If all circuits test normal, replace the ECM.
• If the voltage is greater than the specified range, test for a short to voltage on all the 5-volt reference circuits. If all circuits test normal, replace the ECM.
3. Connect each component associated with the 5-volt reference circuit, one at a time, while monitoring the voltage. The voltage should not change more than 1 volt.
• If the voltage display increases greater than the specified value when a component is connected, test the signal circuit for a short to voltage. If all circuits test normal, replace the ECM.
• If the voltage display decreases more than the specified value when a component is connected, replace the component.
Repair Instructions
Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.
* Camshaft Position Sensor Replacement (Service and Repair)
* Crankshaft Position Sensor Replacement (Crankshaft Position Sensor Replacement)
* Fuel Sender Assembly Replacement (Service and Repair)
* Intake Air Valve Replacement (Service and Repair)
* Control Module References (Programming and Relearning) for ECM replacement, setup, and programming