P0642

DTC P0642 or P0643

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Initial Inspection and Diagnostic Overview
* Review Strategy Based Diagnosis for an overview of the diagnostic approach.
* 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.

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

1. Turn OFF the ignition for 30 seconds or until the ECM powers down.
2. Disconnect the camshaft position (CMP) sensor.
3. Turn ON the ignition, with engine OFF and measure the voltage from the 5-volt reference circuit of the CMP sensor to a good ground with a DMM.

^ If the voltage measures 4.7-5.2 volts, replace the camshaft position sensor.

4. With the DMM still connected to the 5-volt reference circuit, disconnect all other components connected to the 5-volt reference 1, one at a time.

^ If voltage changes when one of the above components is disconnected, replace the component.

5. Test the 5-volt reference 1 circuits for a short to ground or a short to voltage.

^ If no problem was found in the 5-volt reference circuit, replace the ECM.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure. Verification Tests

* Camshaft Position Sensor Replacement
* Crankshaft Position Sensor Replacement
* Fuel Sender Assembly Replacement
* Intake Air Valve Replacement