GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Pontiac 🢒 2004 🢒 Grand Prix 🢒 Engine 🢒 Engine Electrical 🢒 Fuel System Diagnosis

Circuit Description

When you turn ON the ignition switch, the control module enables the fuel pump relay which powers the fuel pump on. The fuel pump remains on as long as the engine is cranking or running and the control module receives ignition reference pulses. If there are no ignition reference pulses, the control module shuts the fuel pump OFF within 2 seconds after the ignition was switched to the on position or if the engine stops.

The fuel tank stores the fuel supply. The electric fuel pump supplies fuel through an in-line fuel filter to the fuel injection system. The fuel pump is an electric pump that is attached to the fuel sender assembly, which is mounted in the fuel tank. The fuel pump is designed to provide fuel at a pressure above the pressure that is needed by the fuel injectors. The fuel pressure regulator, located in the fuel tank, is attached to the fuel sender assembly. The fuel pressure regulator keeps the fuel available to the fuel injectors at a regulated pressure. Unused fuel is returned from the fuel filter to the fuel tank by a separate fuel return pipe.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. This step verifies that the fuel pump is operating.

    2.

  2. This step tests for an internal fuel leak. If the fuel pressure drops during this test, then an internal loss of pressure is indicated.

    3.

  3. This step isolates the condition. Replace the fuel sender assembly, if the fuel pressure remains constant, after closing the valve on the fuel pipe shut-off adapter. Locate and replace the leaking fuel injector if the pressure continues to decrease after closing the valve on the adapter.

    4.

  4. This step isolates the condition. Replace the fuel sender assembly for a stuck open fuel pressure regulator, if the fuel pressure increases above the specified value.

    5.

  5. This step verifies that a circuit condition is not the cause of a fuel pressure concern. Inspect all fuel pump electrical circuits thoroughly.

Step

Action

Values

Yes

No

Schematic Reference: Engine Controls Schematics

Connector End View Reference: Powertrain Control Module Connector End Views or Engine Controls Connector End Views

1

Did you perform the Diagnostic System Check-Engine Controls?

--

Go to Step 2

Go to Diagnostic System Check - Engine Controls

2

Important: Inspect the fuel system for damage, or external leaks, before proceeding with this diagnostic.

  1. Turn ON the ignition, with the engine OFF.
  2. Command the fuel pump ON, with a scan tool.

Does the fuel pump operate?

--

Go to Step 3

Go to Fuel Pump Electrical Circuit Diagnosis

3

Important: Verify there is adequate fuel in the fuel tank before proceeding with this diagnostic.

  1. Turn OFF the ignition.
  2. Turn OFF all of the accessories.

    3. Caution: Wrap a shop towel around the fuel pressure connection in order to reduce the risk of fire and personal injury. The towel will absorb any fuel leakage that occurs during the connection of the fuel pressure gage. Place the towel in an approved container when the connection of the fuel pressure gage is complete.

  3. Install the J 34730-1A fuel pressure gage. Refer to Fuel Pressure Gage Installation and Removal .
  4. Turn ON the ignition, with the engine OFF.

    5. Important: 

       • The fuel pump may need to be commanded to ON a few times in order to obtain the highest possible fuel pressure.
       • Do not start the engine.

  5. Command the fuel pump ON, with a scan tool.
  6. Observe the fuel pressure gage with the fuel pump commanded ON.

Is the fuel pressure within the specified range?

380-410 kPa (55-60 psi)

Go to Step 4

Go to Step 8

4

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

Monitor the fuel pressure gage for 1 minute.

Does the fuel pressure decrease more than the specified value?

34 kPa (5 psi)

Go to Step 7

Go to Step 5

5
  1. Relieve the fuel pressure to the first specified value.
  2. Monitor the fuel pressure gage for 1 minute.

Does the fuel decrease more than the second specified value?

69 kPa (10 psi)

14 kPa (2 psi)

Go to Step 15

Go to Step 6

6
  1. Operate the vehicle within the conditions of the customers concern.
  2. Monitor the fuel trim and HO2S parameters with a scan tool.

Do any of the parameters indicate a lean condition?

--

Go to Step 11

Go to Symptoms - Engine Controls

7

  1. Turn OFF the ignition.
  2. Relieve the fuel pressure. Refer to Fuel Pressure Relief .
  3. Disconnect the fuel feed pipe from the fuel rail. Refer to Metal Collar Quick Connect Fitting Service .
  4. Install the appropriateJ 37287 fuel pipe shut-off adapter between the fuel feed pipe and the fuel rail inlet.
  5. Open the valve on the fuel feed pipe shut-off adapter.
  6. Command the fuel pump ON, with a scan tool.
  7. Bleed the air from the fuel system.
  8. Command the fuel pump ON, with a scan tool.
  9. Close the fuel pipe shut-off valve.
  10. Monitor the fuel pressure gage for 1 minute.

Does the fuel pressure remain constant?

--

Go to Step 15

Go to Step 14

8

Is the fuel pressure above the specified value?

410 kPa (60 psi)

Go to Step 9

Go to Step 10

9

Inspect the fuel return hose/pipe for a restriction.

Did you find and correct the condition?

--

Go to Step 16

Go to Step 15

10

  1. Turn OFF the ignition.
  2. Relieve the fuel system pressure. Refer to Fuel Pressure Relief .
  3. Disconnect the fuel return hose from the fuel return outlet of the fuel filter. Refer to Plastic Collar Quick Connect Fitting Service .
  4. Install the appropriateJ 37287 between the return outlet of the fuel filter and the fuel return hose.
  5. Open the valve in the fuel pipe shut-off adapter.
  6. Turn ON the ignition, with the engine OFF.
  7. Command the fuel pump ON, with a scan tool.
  8. Bleed the air from the fuel system.
  9. Monitor the fuel pressure gauge.

    10. Notice: DO NOT allow the fuel pressure to exceed 517 kPa (75 psi). Excessive pressure may damage the fuel system.

  10. Slowly close the valve in the fuel pipe shut-off adapter.
  11. Use a scan tool in order to command the fuel pump ON.

Does the fuel pressure increase above the specified value?

410 kPa (60 psi)

Go to Step 15

Go to Step 11

11

Inspect the following for a restriction:

    • Fuel filter
        Refer to Fuel Filter Replacement .
    • Fuel feed pipe
        Refer to Fuel System Cleaning .

Did you find and correct the condition?

--

Go to Step 16

Go to Step 12

12

Inspect the harness connectors and ground circuits of the fuel pump for poor connections. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 16

Go to Step 13

13
  1. Remove the fuel sender assembly. Refer to Fuel Sender Assembly Replacement .
  2. Inspect the following items:
    3. • The fuel pump flex hose for damage
    • The in tank fuel pump harness connectors for poor connections
    • The fuel strainer for a restriction
    • Refer to Fuel System Cleaning .
    • Contaminates in the fuel tank

Did you find and correct the condition?

--

Go to Step 16

Go to Step 15

14
  1. Turn OFF the ignition.
  2. Raise the fuel rail, with the fuel lines connected. Refer to Fuel Injection Fuel Rail Assembly Replacement .
  3. Turn ON the ignition, with the engine OFF.
  4. Command the fuel pump ON, with a scan tool.
  5. Locate and replace the leaking fuel injector. Refer to Fuel Injector Replacement .

Did you complete the replacement?

--

Go to Step 16

--

15

Replace the fuel pump and sender assembly. Refer to Fuel Sender Assembly Replacement .

Did you complete the replacement?

--

Go to Step 16

--

16

Operate the system in order to verify the repair.

Did you correct the condition?

--

System OK

Go to Step 3