P0231

CIRCUIT DESCRIPTION
The status of the fuel lift pump is monitored by the powertrain control module (PCM). This signal is also used in order to store a diagnostic trouble code (DTC) if the fuel pump relay is defective or if the fuel lift pump voltage is lost while the engine is running. There should be approximately 12 volts on circuit 120 during the glow plug cycle.

CONDITIONS FOR RUNNING THE DTC
The fuel lift pump is commanded ON.

CONDITIONS FOR SETTING THE DTC
^ The difference between the ignition voltage and the fuel lift pump voltage is more than 4 volts.
^ The condition was met for 2 seconds.

ACTION TAKEN WHEN THE DTC SETS
^ The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
^ The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the 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.

DIAGNOSTIC AIDS
This DTC will not check the fuel lift pump for operation.

TEST DESCRIPTION

Steps 1-10:

Steps 11-18:

The numbers below refer to the step numbers on the diagnostic table.
2. The fuel lift pump can be felt for a pulsing which will also determine if the fuel lift pump is working.
9. This step checks if the PCM is sending a signal to turn the fuel lift pump ON. The scan tool display Lift Pump Voltage will indicate if the feed back voltage is being sent back to the PCM.