GM/Detroit 6.5L ENGINE CONTROLS – DTC P0231 Fuel Pump Feedback Circuit Low Voltage

Circuit Description
The status of the lift pump is monitored by the PCM. This signal is also used to store a DTC if the fuel pump relay is defective or fuel pump voltage is lost while the engine is running. There should be about 12 volts on circuit 120 during glow plug cycle.

Conditions for Running the DTC
• The PCM performs this DTC diagnostic continuously.
• The fuel lift pump is commanded ON.

Conditions for Setting the DTC
• The difference between ignition voltage and fuel pump voltage is more than 4 volts.
• All diagnostic conditions met for 2 seconds.

Action Taken When the DTC Sets
• The PCM illuminates the malfunction indicator lamp (MIL) on the second consecutive drive trip that the diagnostic runs and fails.
• The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the Failure Records will store this information. If the diagnostic reports a failure on the second consecutive drive trip, the Freeze Frame records the operating conditions at the time of failure and updates the Failure Records.

Conditions for Clearing the MIL/DTC
• The PCM will turn the MIL off after three consecutive trips without a fault condition.
• A History DTC clears after forty consecutive warm-up cycles, if this or any other emission related diagnostic does not report any failures
• The use of a scan tool.

Diagnostic Aids
This DTC will not check the fuel pump operation.

Test Description
Number(s) below refer to the step number(s) on the Diagnostic Table.
3. This step checks the fuel lift pump circuit.


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