GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2004 🢒 Seville 🢒 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.

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.

    3.

  3. This step tests the fuel pressure regulator.

  4. This step inspects the fuel pressure regulator for a fuel leak from the vacuum port.

    5.

  5. This step tests for a loss of fuel pressure between the fuel feed pipe shut-off adapter and the fuel pump.

    6.

  6. This step tests for a leaking fuel injector, or fuel pressure regulator.

    7.

  7. This step tests for a restricted fuel return pipe.

    8.

  8. This step determines if the fuel pressure regulator, or the fuel pump, is the cause of the low fuel pressure.

    9.

  9. This step verifies that a circuit condition is not the cause of a fuel pressure concern.

Fuel System Diagnosis

Step

Action

Value(s)

Yes

No

Schematic Reference: 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. Command the fuel pump ON with a scan tool.

Does the fuel pump turn on when commanded with a scan tool?

--

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. Install the fuel pressure gage. Refer to Fuel Pressure Gage Installation and Removal .
  3. Turn ON the ignition, with the engine OFF.
  4. Command the fuel pump ON with a scan tool.

    5. Important: 

       • It may be necessary to command the fuel pump ON a few times, in order to obtain the highest possible fuel pressure.
       • Do not start the engine.

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

Is the fuel pressure within the specified value?

284-325 kPa

(41-47 psi)

Go to Step 4

Go to Step 12

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.

Observe the fuel pressure gage for 1 minute.

Does the fuel pressure drop more than the specified value?

34 kPa (5 psi)

Go to Step 9

Go to Step 5

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

Does the fuel pressure drop more than the second specified value?

69 kPa (10 psi)

14 kPa (2 psi)

Go to Step 25

Go to Step 6

6

  1. Turn OFF the ignition for 15 seconds.
  2. Turn ON the ignition, with the engine OFF.
  3. Observe the fuel pressure gage.
  4. Start the engine.

Does the fuel pressure drop the specified value when the engine is started?

21-69 kPa

(3-10 psi)

Go to Step 7

Go to Step 8

7
  1. Operate the vehicle within the conditions of the customers concern.
  2. Observe the fuel trim parameters with a scan tool

Does the fuel trim parameters indicate a lean condition?

--

Go to Step 17

Go to Symptoms - Engine Controls

8
  1. Disconnect the vacuum hose from the fuel pressure regulator.
  2. Observe the fuel pressure gage.
  3. Idle the engine.
  4. Apply 304-355 mm (12-14 in) of vacuum to the fuel pressure regulator with a hand held vacuum pump.

Does the fuel pressure drop the specified value when the vacuum is applied?

21-69 kPa

(3-10 psi)

Go to Step 22

Go to Step 24

9

  1. Turn OFF the ignition.
  2. Remove the vacuum hose from the fuel pressure regulator.
  3. Turn ON the ignition, with the engine OFF.
  4. Command the fuel pump 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 24

Go to Step 10

10

  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 pipe 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 ON with a scan tool.
  8. Bleed the air from the fuel pressure gage.
  9. Command the fuel pump ON and 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 19

Go to Step 11

11

  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 ON and OFF with a scan tool.
  5. Close the fuel return pipe shut off valve.
  6. Observe the fuel pressure gage for 1 minute.

Does the fuel pressure remain constant?

--

Go to Step 24

Go to Step 20

12

Is the fuel pressure more than the specified value?

427 kPa (62 psi)

Go to Step 14

Go to Step 13

13

Is the fuel pressure more than the specified value?

0 kPa (0 psi)

Go to Step 16

Go to Step 17

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 pipe. Refer to Metal Collar Quick Connect Fitting Service .
  4. Attach a length of flexible fuel hose to the fuel rail outlet passage.
  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. Observe the fuel pressure gage while the fuel pump is operating.

Is the fuel pressure within the specified value?

284-325 kPa

(41-47 psi)

Go to Step 23

Go to Step 15

15

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

Did you find and correct the condition?

--

Go to Step 26

Go to Step 24

16

  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 pipe. Refer to Metal Collar Quick Connect Fitting Service .
  4. Install the J 37287 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. Command the fuel pump ON with a scan tool.
  8. Bleed the air from the fuel system.
  9. Observe the fuel pressure gage.

    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 return pipe shut off adapter.
  11. Command the fuel pump ON with a scan tool.

Does the fuel pressure rise above the specified value?

325 kPa (47 psi)

Go to Step 24

Go to Step 17

17

Inspect the following items for a restriction:

    • Fuel filter
    • Fuel feed pipe

Did you find and correct the condition?

--

Go to Step 26

Go to Step 18

18

Test for an intermittent and for a poor connection at the harness connectors and the ground circuits of the fuel pump. Refer to Testing for Intermittent Conditions and Poor Connections and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 26

Go to Step 19

19
  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 intake fuel pump harness connectors for poor connections
    • The fuel strainer for a restriction
    • Contaminates in the fuel tank

Did you find and correct the condition?

--

Go to Step 26

Go to Step 25

20
  1. Turn OFF the ignition.
  2. Open the fuel return pipe shut off valve.
  3. Relieve the fuel pressure. Refer to Fuel Pressure Relief .
  4. Raise the fuel rail, with the fuel lines connected. Refer to Fuel Injection Fuel Rail Assembly Replacement .
  5. Inspect the fuel injectors for a fuel leak. Refer to Fuel Injector Replacement .

Did you find and correct the condition?

--

Go to Step 26

Go to Step 21

21

    Important: Ensure that the fuel injectors are fully seated in the fuel rail before proceeding with this step.

  1. Position the fuel rail assembly over the intake manifold ports.
  2. Reinstall the fuel rail retaining bolts by hand.
  3. Turn ON the ignition, with the engine OFF.
  4. Observe the fuel pressure gage.
  5. Allow the fuel pressure to drop to the specified value.
  6. Raise the fuel rail in order to locate and replace the leaking fuel injector. Refer to Fuel Injector Replacement .

Did you complete the replacement?

103 kPa (15 psi)

Go to Step 26

--

22

Repair the vacuum source to the fuel pressure regulator.

Did you complete the repair?

--

Go to Step 26

--

23

Locate and repair the restricted fuel return line.

Did you complete the repair?

--

Go to Step 26

--

24

Important: Inspect for a missing, or damaged, fuel pressure regulator 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 26

--

25

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

Did you complete the replacement?

--

Go to Step 26

--

26

Operate the vehicle in order to verify the repair.

Did you correct the condition?

--

System OK

Go to Step 3