P1172

CIRCUIT DESCRIPTION
The fuel pump is located on the left frame rail between the fuel tanks. The Engine Control Module (ECM) provides ignition positive voltage to the coil side of the fuel pump relay. The ECM energizes the fuel pump relay, which applies power to the fuel pump. Fuel is transferred from the rear fuel tank to the front fuel tank in order to ensure all of the usable fuel volume is available to the engine. This Diagnostic Trouble Code (DTC) sets when the ECM commands the transfer fuel pump ON and a predetermined change in the front and rear fuel level sensors does not occur.

CONDITIONS FOR RUNNING THE DTC
^ DTCs P0461, P0462, P0463, P0500, P1431, P1432, P1433 are not set.
^ The engine is running.
^ The vehicle speed is 0 km/h (0 mph).
^ The primary fuel level is less than 25 liters (6.6 gallons).
^ The secondary fuel level is between 3-10 liters (0.7-2.6 gallons).
^ The above conditions are met for 20 seconds before the pump is commanded ON. The fuel pump is commanded ON for 120 seconds.

CONDITIONS FOR SETTING THE DTC
The ECM does not detect a change of 4 liters (1.06 gallons) in the primary and secondary fuel level sensors with the fuel pump commanded ON for 120 seconds.

ACTION TAKEN WHEN THE DTC SETS
^ The control module stores the DTC information into memory when the diagnostic runs and fails.
^ The Malfunction Indicator Lamp (MIL) will not illuminate.
^ The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Failure Records.
^ The driver information center, if equipped, may display a message.

CONDITIONS FOR CLEARING THE DTC
^ 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 non-emission related diagnostic.
^ Use a scan tool in order to clear the DTC.

TEST DESCRIPTION

Steps 1-14:

Steps 15-27:

The numbers below refer to the step numbers on the diagnostic table.
2. This step determines if the condition is on the coil side, or the switch side of the fuel pump relay. Listen for an audible click as the fuel pump relay is commanded ON and OFF. Repeat the commands as necessary in order to verify the fuel pump relay operation.
4. This step tests the control circuit of the fuel pump relay. The test lamp should turn ON and OFF with the scan tool commands. Repeat the commands as necessary.
8. This step verifies the fuel pump operation. Listen for the fuel pump as you command the fuel pump ON. Repeat the commands as necessary in order to verify the fuel pump operation.
9. This step tests the ignition voltage circuit of the fuel pump relay.
10. This step verifies the fuel pump operation. If the test lamp blinks, then the fuel pump and circuits are OK.
13. The rear fuel level sensor voltage must be above the specified value in order to continue with the diagnostic procedure.
15. This step tests for a fuel flow condition. If the rear fuel level sensor voltage does not decrease as the fuel pump is operating, a restriction in the fuel lines or rear sender is the probable cause of the DTC.
16. If a restriction in the fuel lines, or rear fuel sender is not isolated, a mechanical condition exists in the fuel pump. Replace the fuel pump.