GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2004 🢒 TrailBlazer - 2WD 🢒 Brakes 🢒 Hydraulic Brakes 🢒 Fuel System Diagnosis

System Description

The control module enables the fuel pump relay when the ignition switch is turned ON. The control module will disable the fuel pump relay within two seconds unless the control module detects ignition reference pulses. The control module continues to enable the fuel pump relay as long as ignition reference pulses are detected. The control module disables the fuel pump relay within two seconds if ignition reference pulses cease to be detected and the ignition remains ON.

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 pump provides fuel at a higher rate of flow than is needed by the fuel injection system. The fuel pressure regulator maintains the correct fuel pressure to the fuel injection system. A separate pipe returns unused fuel to the fuel tank.

Step

Action

Values

Yes

No

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 relay ON with a scan tool.

Does the fuel pump operate?

--

Go to Step 3

Go to Fuel Pump Electrical Circuit Diagnosis

3

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

  1. Turn OFF the ignition.
  2. Turn OFF all accessories.
  3. Install a 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 relay may need to be commanded ON a few times in order to obtain the highest possible fuel pressure.
       • DO NOT start the engine.

  5. Command the fuel pump relay 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?

345-395 kPa (50-57 psi)

Go to Step 4

Go to Step 10

4

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.

Monitor the fuel pressure gage for 1 minute.

Does the fuel pressure decrease by 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 5 minutes.

Does the fuel pressure decrease by more than the second specified value?

69 kPa (10 psi)

14 kPa (2 psi)

Go to Step 21

Go to Step 6

6
  1. Operate the vehicle within the conditions to reproduce the original symptoms.
  2. Monitor the O2 and the fuel trim parameters with a scan tool.

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

--

Go to Step 15

Go to Symptoms - Engine Controls

7
  1. Turn OFF the ignition.
  2. Disconnect the fuel pressure regulator vacuum tube.
  3. Turn ON the ignition, with the engine OFF.
  4. Command the fuel pump relay ON with a scan tool.
  5. Inspect for a fuel leak from the fuel pressure regulator vacuum port.

Is the fuel pressure regulator leaking fuel?

 

Go to Step 20

Go to Step 8

8

  1. Turn OFF the ignition.
  2. Relieve the fuel pressure. Refer to Fuel Pressure Relief .
  3. Disconnect the fuel feed hose and the fuel return hose from the fuel rail pipes. Refer to Metal Collar Quick Connect Fitting Service .
  4. Install the J 37287 Fuel Line Shut-off Adapters between the fuel hoses and the fuel rail pipes.
  5. Open the valves on the fuel pipe shut-off adapters.
  6. Turn ON the ignition, with the engine OFF.
  7. Command the fuel pump relay ON with a scan tool.
  8. Bleed the air from the fuel pressure gage.
  9. Command the fuel pump relay ON and then OFF with a scan tool.
  10. Close the fuel feed pipe shut-off valve.
  11. Monitor the fuel pressure gage for 1 minute.

Does the fuel pressure remain constant?

--

Go to Step 9

Go to Step 17

9

  1. Turn OFF the ignition.
  2. Open the fuel feed pipe shut-off valve.
  3. Turn ON the ignition, with the engine OFF.
  4. Command the fuel pump relay ON and then OFF with a scan tool.
  5. Close the fuel return pipe shut-off valve.
  6. Monitor the fuel pressure gage for 1 minute.

Does the fuel pressure remain constant?

--

Go to Step 20

Go to Step 18

10

Is the fuel pressure more than the specified value?

395 kPa (57 psi)

Go to Step 12

Go to Step 11

11

Is the fuel pressure more than the specified value?

0 kPa (0 psi)

Go to Step 14

Go to Step 15

12

  1. Turn OFF the ignition.
  2. Relieve the fuel pressure. Refer to Fuel Pressure Relief .
  3. Disconnect the fuel return hose from the fuel rail return pipe. Refer to Metal Collar Quick Connect Fitting Service .
  4. Attach a length of flexible hose to the fuel rail return pipe.
  5. Place the open end of the flexible fuel hose into an approved gasoline container.
  6. Turn ON the ignition, with the engine OFF.
  7. Monitor the fuel pressure gage while the fuel pump is operating.

Is the fuel pressure within the specified range?

345-395 kPa (50-57 psi)

Go to Step 19

Go to Step 13

13

Inspect the fuel rail outlet passage and the fuel rail return pipe for a restriction.

Did you find and correct the condition?

--

Go to Step 22

Go to Step 20

14

  1. Turn OFF the ignition.
  2. Relieve the fuel pressure. Refer to Fuel Pressure Relief .
  3. Disconnect the fuel return hose from the fuel rail return pipe. Refer to Metal Collar Quick Connect Fitting Service .
  4. Install the J 37287 Fuel Line Shut-off Adapter between the fuel return pipe and the fuel rail.
  5. Open the valve in the fuel pipe shut-off adapter.
  6. Turn ON the ignition, with the engine OFF.
  7. Bleed the air from the fuel pressure gage.
  8. Monitor the fuel pressure gage.

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

  9. Command the fuel pump relay ON with a scan tool.
  10. Slowly close the valve in the fuel return pipe shut-off adapter, while the fuel pump is operating.

Does the fuel pressure increase to more than the specified value?

395 kPa (57 psi)

Go to Step 20

Go to Step 15

15

Inspect the following components for a restriction:

    • The fuel filter
    • The fuel feed pipe

Did you find and correct the condition?

--

Go to Step 22

Go to Step 16

16

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 22

Go to Step 17

17

  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
    • The fuel tank for contaminants

Did you find and correct the condition?

--

Go to Step 22

Go to Step 21

18

  1. Turn OFF the ignition.
  2. Raise the fuel rail with the fuel pipes 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 22

 

19

Repair the restricted fuel return pipe.

Did you complete the repair?

--

Go to Step 22

--

20

Important: Inspect for a missing or damaged O-ring seal before replacing the fuel pressure regulator.

Replace the fuel pressure regulator. Refer to Fuel Pressure Regulator Replacement .

Did you complete the replacement?

--

Go to Step 22

--

21

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

Did you complete the replacement?

--

Go to Step 22

--

22

Operate the system in order to verify the repair.

Did you correct the condition?

--

System OK

Go to Step 3