GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Pontiac 🢒 2009 🢒 Vibe - AWD 🢒 Diagnostic Navigation 🢒 Vehicle Diagnostic Information 🢒 Fuel System Diagnosis

Diagnostic Instructions
    • Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
    • Review Strategy Based Diagnosis for an overview of the diagnostic approach.
    •  Diagnostic Procedure Instructions provides an overview of each diagnostic category.

Circuit/System Description

The fuel supply system is a returnless design. Most of the fuel system components are located inside the fuel tank. When the ignition switch is turned to the START position and the engine is cranking, the circuit opening relay energizes the fuel pump. The fuel pump will continue to operate if the powertrain control module (PCM) receives a reference signal when the engine is started. The fuel pump operates as long as the circuit opening relay is energized by the PCM. When the circuit opening relay is de-energized, the fuel pump will stop operating. The fuel pump delivers fuel to the fuel rail at high pressure. The fuel pressure regulator, located in the fuel tank, is responsible for keeping the fuel pressure at 301-347 kPa (44-50 psi).

Diagnostic Aids
    • Monitoring the misfire current counters, or misfire graph, may help to isolate the fuel injector that is causing the condition.
    • Operating the vehicle over a wide temperature range may help isolate the fuel injector that is causing the condition.
    • If you were sent here by a DTC P0300 and all the injectors test normal, the Misfire Current Cylinder or Misfire Graphic information on a scan tool can be used to determine which injector circuit should be examined in detail.

Reference Information

Schematic Reference

Engine Controls Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Fuel System Description

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

Special Tools

    • J 34730-1A Fuel Pressure Gage
    • J 42982 Fuel Pressure Gage Adapter
    • J 37287 Fuel Line Shut-Off Adapters

Circuit/System Verification

    Important: 

       • Inspect the fuel system for damage or external leaks before proceeding.
       • Verify that adequate fuel is in the fuel tank before proceeding.
       • The fuel pump relay may need to be commanded ON a few times in order to obtain the highest possible fuel pressure.
       • DO NOT start the engine.

  1. Ignition ON, command the fuel pump relay ON with a scan tool. You should hear the fuel pump turn ON and OFF.
    2. ⇒If the fuel pump does not turn ON, refer to Fuel Pump Electrical Circuit Diagnosis.
  2. Ignition OFF, install the J 34730-1A and J 42982 . Refer to Fuel Pressure Gage Installation and Removal.
  3. Ignition ON, command the fuel pump relay ON with a scan tool. Verify the fuel pressure is between 301-347 kPa (44-50 psi) and does not decrease to less than 147 kPa (21 psi) for 5 minutes.

Circuit/System Testing
  1. Ignition ON, command the fuel pump relay ON with a scan tool and observe the fuel pressure gage while the fuel pump is operating. Verify the fuel pressure is between 301-347 kPa (44-50 psi).
    2. ⇒If greater than the specified range, replace the fuel pressure regulator. Test again for fuel pressure between 301-347 kPa (44-50 psi). If still greater than the specified value, replace the fuel pump.
    ⇒If less than the specified range, remove the fuel tank and test for any of the following conditions:
    • Restricted fuel feed pipe
    • Restricted or plugged fuel filter
    • Restricted or plugged strainer
    • Stuck or binding fuel level float
    • Faulty fuel pressure regulator
    • Poor connections at the harness connectors and ground circuits of the fuel pump
    ⇒If you find a condition, repair as necessary.
    ⇒If all conditions test normal, replace the fuel pump.

    Important: The fuel pressure may vary slightly when the fuel pump stops operating. After the fuel pump stops operating, the fuel pressure should stabilize and remain constant.

  2. Verify the fuel pressure does not decrease to less than 147 kPa (21 psi) for 5 minutes.
    3. ⇒If the fuel pressure decreases greater than the specified value, perform the following procedure:
    2.1. Ignition OFF, relieve the fuel pressure. Refer to Fuel Pressure Relief.
    2.2. Install the J 37287 between the fuel feed pipe and the J 42982 .
    2.3. Open the valve on the J 37287 .
    2.4. Ignition ON, command the fuel pump relay ON with a scan tool and bleed the air from the fuel pressure gage.
    2.5. Close the valve on the J 37287 .
    2.6. Verify the fuel pressure does not decrease to less than 147 kPa (21 psi) for 5 minutes.
    ⇒If the fuel pressure remains constant, replace the fuel pump.
    ⇒If the fuel pressure is less than the specified range, locate and replace the leaking fuel injector.
  3. Ignition OFF, remove the J 34730-1A and J 42982 . Refer to Fuel Pressure Gage Installation and Removal.
  4. Operate the vehicle within the conditions of the customer concern while monitoring fuel related parameters with a scan tool.
    5. ⇒If the scan tool parameters indicate a lean condition, test/inspect for the following conditions:
    • Restricted fuel feed pipe
    • Faulty fuel pressure regulator
    • Poor connections at the harness connectors and ground circuits of the fuel pump
⇒If the fuel system components test normal, refer to Symptoms - Engine Controls.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  Fuel Pump and Fuel Filter Assembly Replacement
    •  Fuel Tank Replacement
    •  Fuel Pressure Regulator Replacement