Circuit Description
The engine control module (ECM) provides 5 volts to the following sensors:
| • | The oil pressure sensor |
| • | The exhaust gas recirculation (EGR) valve |
| • | The accelerator pedal position (APP) 1 sensor |
| • | The rail pressure sensor |
These 5-volt reference circuits are independent of each other outside the ECM, but are bussed together inside the ECM. Therefore, a circuit condition on one sensor 5-volt reference circuit may affect the other sensor 5-volt reference circuits. The ECM monitors the voltage on the 5-volt reference circuit. If the ECM detects a high voltage condition, DTC P0643 sets.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P0643 5-Volt Reference 1 Circuit High Voltage
Conditions for Running the DTC
| • | The ignition is ON. |
| • | DTC P0643 runs continuously. |
Conditions for Setting the DTC
| • | The ECM detects the 5-volt reference 1 circuit voltage is more than 5.2 volts. |
| • | The above condition is present for longer than 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. |
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics Connector End View Reference: Engine Control Module Connector End Views or Engine Controls Connector End Views | ||||
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | Go to Diagnostic System Check - Vehicle in Vehicle DTC Information |
2 |
Is the 5-Volt Reference 1 parameter more than the specified value? | 5.2 V | Go to Step 3 | Go to Intermittent Conditions |
3 | Test each 5-volt reference 1 circuits for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 6 | Go to Step 4 |
4 | Replace the engine control module (ECM). Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 6 | -- |
5 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 6 |
6 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information | System OK |
