For a complete wiring diagram Refer to Section 8W.1. CHECKING THE FUEL PUMP CIRCUITSTurn the ignition on.Diagnose and repair any fuel pump control circuit or relay DTCs before continuing with this test.Disconnect the Fuel Pump Module harness connector.Connect a test light between the (N1) Fuel Pump Control Output circuit and the (Z905) Ground circuit at the Fuel Pump Module harness connector (body side).With a scan tool, actuate the fuel pump control to ON (100%).Stop all actuation tests before continuing.Does the test light illuminate brightly?YesGo to 2NoGo to 82. CHECKING THE FUEL PRESSURETurn the ignition off.The fuel system is under a constant pressure even with the engine off. Before testing or servicing any fuel system Line, fitting or line, the fuel system pressure must be released. Failure to follow these instructions can result in personal injury or death. Disconnect the Low Pressure Fuel Supply Line from the inlet port of the Fuel Injection Pump.Install a fuel pressure gauge in the disconnected Low Pressure Fuel Supply Line.Turn the ignition on.With the scan tool, actuate the fuel pump relay control. Observe the fuel pressure gauge.The fuel pressure specification is between 4.5 and 6.0 bar ( 65 and 87 psi. ). Stop all actuation tests before continuing.Select the conclusion that best matches the result of the test:Fuel pressure is within the stated specificationGo to 6Fuel pressure is below the stated specificationGo to 3Fuel pressure is above the stated specificationReplace the Fuel Filter/Water Separator.Perform the PCM Verification Test.(Refer to 9 - ENGINE - STANDARD PROCEDURE)3. RESTRICTED LOW PRESSURE FUEL SUPPLY LINE Turn the ignition off.The fuel system is under a constant pressure, even with the engine off. Before testing or servicing any fuel system Line, fitting or line, the fuel system pressure must be released. Failure to follow these instructions can result in personal injury or death.Reconnect the Low Pressure Fuel Supply Line from the inlet port of the Fuel Injection PumpDisconnect the Low Pressure Fuel Supply Line from the inlet port of the Fuel Filter/Water Separator.Install a fuel pressure gauge in the disconnected Low Pressure Fuel Supply Line.Turn the ignition on.With the scan tool, actuate the fuel pump relay control. Observe the fuel pressure gauge.The fuel pressure specification is between 4.5 and 6.0 bar ( 65 and 87 psi. ).Stop all actuation tests before proceeding.Is the fuel pressure within specification?YesReplace the Fuel Filter/Water Separator.Perform the PCM Verification Test.(Refer to 9 - ENGINE - STANDARD PROCEDURE)NoGo to 44. RESTRICTED INJECTOR BACK FLOW LINE Turn the ignition off.The fuel system is under a constant pressure, even with the engine off. Before testing or servicing any fuel system Line, fitting or line, the fuel system pressure must be released. Failure to follow these instructions can result in personal injury or death.Disconnect the Injector Back Flow Pressure Fuel Line from the Low Pressure Fuel Supply Line.The Injector Back Flow Pressure Fuel Line is connected to the Low Pressure Fuel Supply Line approximately six inches away from the Fuel Filter/Water Separator.Install a cap to block the port where the Injector Back Flow Pressure Fuel Line was connected.Install a fuel pressure gauge in the disconnected Low Pressure Fuel Supply Line.Turn the ignition on.With the scan tool, actuate the fuel pump relay control. Observe the fuel pressure gauge.The fuel pressure specification is between 4.5 and 6.0 bar ( 65 and 87 psi. ).Stop all actuation tests before proceeding.Is the fuel pressure within specification?YesGo to 6NoGo to 55. FUEL PUMP MODULETurn the ignition off.The fuel system is under a constant pressure even with the engine off. Before testing or servicing any fuel system Line, fitting or line, the fuel system pressure must be released. Failure to follow these instructions can result in personal injury or death.Reconnect the Low Pressure Fuel Supply Line from the inlet port of the Fuel Filter/Water Separator.Reconnect the Injector Back Flow Pressure Fuel Line.Disconnect the Low Pressure Fuel Supply Line from the outlet port of the Fuel Module on top of the Fuel Tank.Install a fuel pressure gauge in the outlet port of the Fuel Pump Module.Turn the ignition on.With the scan tool, actuate the fuel pump relay control. Observe the fuel pressure gauge.The fuel pressure specification is between 4.5 and 6.0 bar ( 65 and 87 psi. ).Stop all actuation tests before proceeding.Is the fuel pressure within specification?YesReplace the Fuel Pump Module.Perform the PCM Verification Test.(Refer to 9 - ENGINE - STANDARD PROCEDURE)NoGo to 66. FUEL PRESSURE SOLENOID BACK FLOW RETURN LINETurn the ignition off.Disconnect the Back Flow Return Line at the Fuel Pressure Solenoid.Disconnect the Back Flow Return Line at the Fuel Pump Module on top of the Fuel TankApply air pressure to the Solenoid end of the Back Flow Return Line.Is air movement evident at the Fuel Pump Module end of the Back Flow Return Line?YesTest CompleteNoGo to 77. HIGH PRESSURE PUMP BACK FLOW RETURN LINETurn the ignition off.Reconnect the Back Flow Return Line at the Fuel Pressure Solenoid.Disconnect the Back Flow Return Line at the High Pressure Fuel Pump.Apply air pressure to the High Pressure Pump end of the Back Flow Return Line.Is air movement evident at the Fuel Pump Module end of the Back Flow Return Line?YesTest CompleteNoRepair the Back Flow Return Line for kinks or broken line.Perform the PCM Verification Test.(Refer to 9 - ENGINE - STANDARD PROCEDURE)8. (Z905) FUEL PUMP GROUND CIRCUIT OPEN OR HIGH RESISTANCETurn the ignition off.Disconnect the Fuel Pump Module harness connector.Using a 12 volt test light connected to 12 volts, check the (Z905) Fuel Pump Motor Ground circuit at the Fuel Pump Module harness connector.The test light should be illuminated and bright. Compare the brightness to that of a direct connection to the battery.Is the test light illuminated and bright?YesGo to 9NoRepair the (Z905) Fuel Pump Ground circuit for an open circuit or high resistance.Perform the PCM Verification Test.(Refer to 9 - ENGINE - STANDARD PROCEDURE)9. (N1) FUEL PUMP CONTROL OUTPUT CIRCUIT CHECKUsing a 12 volt test light connected to 12 volts, check the (N1) Fuel Pump Motor Ground circuit at the Fuel Pump Module harness connector.Turn the ignition on.With a scan tool, actuate the fuel pump control to ON (100%).The test light should be illuminated and bright. Compare the brightness to that of a direct connection to the battery.Is the test light illuminated and bright?YesReplace the Fuel Pump Module in accordance with the Service information.Perform the PCM Verification Test.(Refer to 9 - ENGINE - STANDARD PROCEDURE)NoRepair the (N1) Fuel Pump Control Output circuit for an open, short to ground or short to voltage. If the Fuel Pump Control Output circuit is o.k., replace the Totally Integrated Power Module.Perform the PCM Verification Test.(Refer to 9 - ENGINE - STANDARD PROCEDURE)