DTC P0642 or P0643. Chevrolet Express

For 1990-2009 cars only

Makes 🢒 Chevrolet 🢒 2007 🢒 Express - AWD 🢒 Safety and Security 🢒 Supplemental Inflatable Restraints 🢒 DTC P0642 or P0643

Diagnostic Instructions

•	Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

•	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	Short to Ground	High Resistance	Open	Short to Voltage	Signal Performance
Crankshaft 58 X - 5-Volt Reference	P0642	P0336	P0335	P0643 P0336	--
Camshaft 4 X - 5-Volt Reference	P0642	P0340	P0340	P0643 P0336	--

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.

•	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

•	The control module illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails.

•	The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame/Failure Records.

Conditions for Clearing the MIL/DTC

•	The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.

•	A current DTC, Last Test Failed, clears when the diagnostic runs and passes.

•	A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.

•	Clear the MIL and the DTC with a scan tool.

Reference Information

Schematic Reference

Engine Controls Schematics

Connector End View Reference

•	Engine Control Module Connector End Views

•	Engine Controls Connector End Views

Electrical Information Reference

•	Circuit Testing

•	Connector Repairs

•	Testing for Intermittent Conditions and Poor Connections

•	Wiring Repairs

Circuit/System Verification

Engine starts and runs.
Engine running, observe the DTC information with a scan tool. DTCs P0642 or P0643 should not set.
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

Turn OFF the ignition for 30 seconds or until the ECM powers down.
Disconnect the camshaft position (CMP) sensor.
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.

With the DMM still connected to the 5-volt reference circuit, disconnect the crankshaft position (CKP) sensor.

⇒	If the voltage measures 4.7-5.2 volts, replace the CKP sensor.

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.

•	Camshaft Position Sensor Replacement

•	Crankshaft Position Sensor Replacement

•	Control Module References for ECM replacement, setup, and programming