P0642

DTC P0642

DTC DESCRIPTORS

DTC P0642
5-Volt Reference 1 Circuit Low Voltage

DTC P0643
5-Volt Reference 1 Circuit High Voltage

DIAGNOSTIC FAULT INFORMATION






IMPORTANT: Always perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

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.
- 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.

CIRCUIT/SYSTEM VERIFICATION
Engine starts and runs.

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 the crankshaft position (CKP) sensor.
- If the voltage measures 4.7-5.2 volts, replace the CKP sensor.
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

IMPORTANT: Always perform the Diagnostic Repair Verification after completing the diagnostic procedure.
- Camshaft Position (CMP) Sensor Replacement
- Crankshaft Position (CKP) Sensor Replacement
- Control Module References for ECM replacement, setup, and programming.