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

Circuit Description

When the ignition is turned ON, the powertrain control module (PCM) supplies power to the in-tank fuel pump, by energizing the fuel pump relay. This action supplies battery voltage to the fuel pump via the fuel pump module. The in-tank fuel pump remains ON as long as the engine is cranking or running and the PCM receives crankshaft reference pulses. If there are no reference pulses, the PCM turns the in-tank fuel pump OFF, 2 seconds after the ignition switch is turned ON or 2 seconds after the engine stops running. The electric fuel pump is incorporated into the modular fuel pump and sender assembly design and is located inside the fuel tank. The fuel pump supplies fuel through a fuel filter, also located in the modular fuel pump and sender assembly, through the fuel feed pipes, to the fuel rail assembly. The fuel pump provides fuel at a pressure above the pressure needed by the fuel injectors. The fuel pressure regulator, located in the base of the modular fuel pump and sender assembly, keeps the fuel available to the fuel injectors at a regulated pressure. When the fuel pressure rises above the pressure regulator calibration, the pressure is relieved, with excess fuel exhausted into the modular fuel pump and sender assembly reservoir.

Test Description

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

  1. The Diagnostic System Check-Engine Controls prompts the technician to complete some basic checks and store the Freeze Frame data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.

    2.

  2. This step determines whether the fuel pump can provide fuel within the correct regulated pressure range.

    3.

  3. This step tests that the fuel system can maintain fuel pressure with the pump Off. A fuel pressure drop of more than 34 kPa (5 psi) within the specified time indicates a leak in the fuel system.

    4.

  4. This step tests for a restriction in the fuel system.

Step

Action

Values

Yes

No

Schematic Reference: Engine Controls Schematics Fuel Hose/Pipes Routing Diagram

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. Use a scan tool in order to command the fuel pump ON. Refer to Scan Tool Output Controls .

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.
  4. Place the bleed hose of the fuel pressure gage into an approved gasoline container.
  5. Turn ON the ignition, with the engine OFF.
  6. Use a scan tool in order to command the fuel pump ON.
  7. Bleed the air out of the fuel pressure gage.

    8. 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.

  8. Observe the fuel pressure gage, with the fuel pump commanded ON.

Is the fuel pressure within the specified value?

380-440 kPa (55-64 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 drop 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 drop more than the second specified value?

69 kPa (10 psi)

14 kPa (2 psi)

Go to Step 13

Go to Step 6

6
  1. Operate the vehicle within the conditions of the customers concern.
  2. Use a scan tool in order to monitor the fuel related parameters.

Do any of the scan tool parameters indicate a lean condition?

--

Go to Step 9

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 J 37287 fuel pipe shut-off adapter between the fuel pipe and the fuel rail.
  5. Open the valve on the fuel feed pipe shut-off adapter.
  6. Use a scan tool in order to command the fuel pump ON.
  7. Bleed the air from the fuel pressure gage.
  8. Close the fuel feed pipe shut-off valve.
  9. Monitor the fuel pressure gage for 1 minute.

Does the fuel pressure remain constant?

--

Go to Step 13

Go to Step 12

8

Is the fuel pressure more than the specified value?

440 kPa (64 psi)

Go to Step 13

Go to Step 9

9

Inspect the harness connectors and the 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 14

Go to Step 10

10

Inspect the fuel feed pipe for a restriction.

Did you find and correct the condition?

--

Go to Step 14

Go to Step 11

11

Inspect for a restricted or plugged fuel filter. Refer to Fuel Filter Replacement .

Did you find and correct the condition?

--

Go to Step 14

Go to Step 13

12
  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 relay 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 14

--

13

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

Did you complete the replacement?

--

Go to Step 14

--

14

Operate the system in order to verify the repair.

Did you correct the condition?

--

System OK

Go to Step 3