GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Pontiac 🢒 2006 🢒 Vibe - AWD 🢒 Vehicle Control Systems 🢒 Vehicle DTC Information 🢒 Fuel System Diagnosis

System Description

The fuel supply system is a returnless design that has most of the fuel system components located inside of the fuel tank. When the ignition switch is turned to the START position and the engine is cranking, the circuit opening relay will be energized in order to allow the fuel pump to operate and pressurize the system. 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).

Test Description

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

  1. The Diagnostic System Check - Vehicle 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 checks the fuel pump for a worn bearing or a binding impeller. The pump should have a smooth and steady low humming sound. A loud humming or growling noise may indicate a faulty fuel pump. Check a known good vehicle in order to compare pump operation.

    3.

  3. The fuel system can not maintain constant fuel pressure with a leak in any of the following areas:

    • The fuel pump check valve
    • The valve or valve seat within the fuel pressure regulator
    • The fuel injectors

  1. This step checks whether the fuel system is leaking between the fuel pressure gage and the fuel injectors or between the fuel pressure gage and the fuel sender assembly.

    2.

  2. This step checks for additional conditions that can cause low fuel pressure other than a faulty fuel pump. Check for any restrictions or blockage in the fuel feed lines and hoses, including those inside the fuel tank. Check the fuel pump electrical circuit for excessive resistance. Proper fuel pump operation requires correct voltage and adequate current flow.

    3.

  3. Check for rust and other foreign materials in the fuel tank. Clean or replace the fuel tank as necessary.

Step

Action

Values

Yes

No

1

Did you perform the Diagnostic System Check - Vehicle?

--

Go to Step 2

Go to Diagnostic System Check - Vehicle in Vehicle DTC Information

2
  1. Turn OFF the ignition.
  2. Relieve the fuel pressure. Refer to Fuel Pressure Relief .
  3. Install a fuel pressure gage. Refer to Fuel Pressure Gage Installation and Removal .
  4. Install a scan tool.
  5. Turn ON the ignition, with the engine OFF.
  6. Select Fuel Pump in the Engine Output Controls menu of the scan tool.
  7. Turn ON the fuel pump, using the scan tool.
  8. Observe the fuel pressure indicated by the fuel pressure gage with the fuel pump running.

Is any fuel pressure indicated?

--

Go to Step 3

Go to Step 5

3
  1. Turn ON the fuel pump, using the scan tool.
  2. Observe the fuel pressure indicated by the fuel pressure gage with the fuel pump running.

Is the fuel pressure within the specified range?

301-347 kPa

(44-50 psi)

Go to Step 12

Go to Step 4

4

Is the fuel pressure more than the specified value?

347 kPa (50 psi)

Go to Step 22

Go to Step 6

5

Was the fuel pump relay diagnostic performed?

--

Go to Step 24

Go to Fuel Pump Electrical Circuit Diagnosis

6

  1. Remove the bottom cushion of the rear seat in order to gain access to the fuel sender assembly access panel.
  2. Turn ON the ignition, with the engine OFF.
  3. Place a listening device against the access panel.
  4. Command the fuel pump ON with the scan tool.
  5. Listen for audible fuel pump operation. The fuel pump should have a smooth and steady low humming sound.

Is the fuel pump operating as described?

--

Go to Step 7

Go to Step 24

7

Measure the resistance of the fuel pump, with a DMM.

Is the fuel pump resistance within the specified value?

0.2-3.0 ohms at 20°C (68°F)

Go to Step 8

Go to Step 24

8
  1. Visually and physically inspect the fuel feed pipe for the following conditions:
    2. • Any kinks
    • Any cracks
    • An incorrect routing
    • Any restrictions
  2. Repair as necessary.

Was a repair necessary?

--

Go to Step 25

Go to Step 9

9
  1. Remove the fuel sender assembly. Refer to Fuel Sender Assembly Replacement .
  2. Visually and physically inspect the fuel pump strainer for being plugged.

Was the fuel pump strainer found to be plugged?

--

Go to Step 23

Go to Step 10

10
  1. Visually and physically inspect the seals and the O-rings between the fuel pump, the fuel filter, and the fuel pressure regulator for any of the following conditions:
    2. • Any cracks
    • Any splits
    • Any deformation
    • Any missing components
  2. Repair as necessary.

Was a repair necessary?

--

Go to Step 25

Go to Step 11

11
  1. Check the fuel filter for a restriction.
  2. Replace the fuel filter, if necessary. Refer to Fuel Pump and Fuel Filter Assembly Replacement .

Was the fuel filter replaced?

--

Go to Step 25

Go to Step 22

12

  1. Turn ON the fuel pump with the scan tool.
  2. Wait for the fuel pressure to stabilize.
  3. Turn OFF the fuel pump.
  4. Monitor the fuel pressure on the fuel gage.

Does the fuel pressure remain equal to or more than the specified value for 5 minutes after the fuel pump is turned OFF?

147 kPa (21 psi)

Go to Step 13

Go to Step 17

13

Does the fuel pressure decrease during acceleration, cruise, or hard cornering?

--

Go to Step 14

Go to Intermittent Conditions

14

Visually and physically inspect the following items for restrictions:

    • The fuel filter
    • The fuel feed pipe

Was a restriction found?

--

Go to Step 15

Go to Step 16

15

Repair the restriction as necessary.

Is the action complete?

--

Go to Step 25

--

16
  1. Visually and physically inspect for any of the following conditions:
    2. • A restricted fuel pump strainer
    • An incorrectly positioned fuel pump pick-up
    • The incorrect fuel pump
    • A loose or missing fuel pump or tank baffle
  2. Repair as necessary.

Was a repair necessary?

--

Go to Step 25

Go to Step 24

17

  1. Turn ON the fuel pump with the scan tool.
  2. Pinch off the fuel pressure gage adapter hose on the fuel tank side, while monitoring the fuel gage.
  3. Turn OFF the fuel pump.

Does the fuel pressure remain equal to or more than the specified value for 5 minutes after the fuel pump is turned OFF?

147 kPa (21 psi)

Go to Step 19

Go to Step 18

18
  1. Check for a fuel leak in the following areas:
    2. • At the base of the fuel injectors
    • At the fuel injectors
    • At the fuel rail
  2. Repair as necessary.

Was a repair necessary?

--

Go to Step 25

Go to Fuel Injector Solenoid Coil Test - Engine Coolant Temperature Between 10-35 Degrees C (50-95 Degrees F)

19
  1. Check the fuel feed pipe for leaks.
  2. Repair as necessary.

Was a repair necessary?

--

Go to Step 25

Go to Step 20

20

  1. Remove the fuel sender assembly. Refer to Fuel Sender Assembly Replacement .
  2. Visually and physically inspect the seals and O-rings between the fuel pump, the fuel filter, and the fuel pressure regulator for the following conditions:
    3. • Any cracks
    • Any splits
    • Any deformation
    • Any missing components
  3. Inspect the entire fuel pump electrical circuit. Verify B+ at the fuel pump connector and less than 5.0 ohms to ground.
  4. Repair as necessary.

Was a repair necessary?

--

Go to Step 25

Go to Step 21

21
  1. Check the fuel filter and the fuel pump for cracks or a leaking seam.
  2. Replace as necessary.

Was a component replacement necessary?

--

Go to Step 25

Go to Step 22

22
  1. Replace the fuel pressure regulator. Refer to Fuel Pressure Regulator Replacement .
  2. Attempt to start and run the engine.
  3. Monitor the fuel pressure gage while the engine is running.

Is the fuel pressure within the specified value?

301-347 kPa

(44-50 psi)

Go to Step 25

Go to Step 24

23

  1. Replace the fuel pump strainer.
  2. Inspect the fuel system for the cause of the plugged fuel pump strainer.
  3. Repair as necessary.

Is the action complete?

--

Go to Step 25

--

24

Replace the fuel pump. Refer to Fuel Pump and Fuel Filter Assembly Replacement .

Is the action complete?

--

Go to Step 25

--

25
  1. Attempt to start and run the engine.
  2. Monitor the fuel pressure gage while the engine is running.

Is the fuel pressure within the specified value?

301-347 kPa

(44-50 psi)

System OK

Go to Step 2