For 1990-2009 cars only
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 VoltageDTC 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 | -- |
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. |
Reference Information
Schematic Reference
Connector End View Reference
Electrical Information Reference
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.
- With the DMM still connected to the 5-volt reference circuit, disconnect the crankshaft position (CKP) sensor.
- Test the 5-volt reference 1 circuits for a short to ground or a short to voltage.
| ⇒ | If the voltage measures 4.7-5.2 volts, replace the camshaft position sensor. |
| ⇒ | If the voltage measures 4.7-5.2 volts, replace the CKP sensor. |
| ⇒ | 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.
| • | Control Module References for ECM replacement, setup, and programming |
