GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2003 🢒 CTS - RHD 🢒 Engine 🢒 Engine Electrical 🢒 Fuel System Diagnosis

System Description

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

The fuel pump is an electric pump that is attached to the right fuel tank module assembly. The fuel pump also supplies fuel to the siphon jet pump, also attached to the right fuel tank module. The siphon jet pump draws fuel from the left side of the fuel tank to the right side of the fuel tank. The fuel pump is designed to provide fuel at a pressure above the pressure that is needed by the fuel injectors. Unused fuel is returned to the fuel tank by a separate fuel return pipe. A fuel pressure regulator, which is located on the fuel rail assembly, keeps the fuel available to the fuel injectors at a regulated pressure. The port on the fuel pressure regulator is an atmospheric vent. The fuel pressure regulator does not compensate for changes in intake manifold vacuum.

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 verifies that the vehicle is not out of fuel. If the right fuel sender is below 0.8 V, and the left fuel sender is above 0.8 V, a fuel transfer condition exists.

    3.

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

    4.

  4. This step inspects the fuel pressure regulator for a fuel leak from the atmospheric vent. If fuel leaks from the fuel pressure regulator while the fuel pump is commanded ON, replace the fuel pressure regulator.

    5.

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

    6.

  6. This step tests for a leaking fuel injector or fuel pressure regulator. If the fuel pressure remains constant during this test, the fuel injectors are not leaking fuel.

    7.

  7. This step tests for a restricted fuel return pipe. If the fuel pressure is within the specified values, a restriction in the fuel return pipe is indicated.

    8.

  8. This step determines if the fuel pressure regulator, or the fuel pump, is the cause of the low fuel pressure. If the pressure rises above the specified value, the fuel pump is OK.

    9.

  9. 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

Value(s)

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 the following conditions before proceeding with this diagnostic procedure:

   • Damage to the fuel system
   • External fuel leaks

  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

Observe the fuel level sensor left voltage with a scan tool.

Is the fuel level sensor left voltage less than the specified value?

0.8 V

Go to Step 4

Go to Step 6

4

Observe the fuel level sensor right voltage with a scan tool.

Is the fuel level sensor right voltage less than the specified value?

0.8 V

Go to Step 5

Go to Step 18

5
  1. Add the specified amount of fuel.
  2. Operate the vehicle within the conditions of the customer's concern.
  3. Monitor the fuel trim related parameters with a scan tool. Refer to Scan Tool Data List .

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

19 liters (5 gallons)

Go to Step 20

Go to Symptoms - Engine Controls

6
  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. Important: 

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

  4. Command the fuel pump ON with a scan tool.
  5. Observe the fuel pressure gage, while the fuel pump is operating.

Is the fuel pressure within the specified range?

337-379 kPa (49-55 psi)

Go to Step 7

Go to Step 13

7

Important: The fuel pressure will drop when the fuel pump stops operating. After the fuel pump stops operating, the fuel pressure should stabilize and remain constant.

  1. Allow the fuel pressure to stabilize.
  2. 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 10

Go to Step 8

8
  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 26

Go to Step 9

9
  1. Operate the vehicle within the conditions of the customer's concern.
  2. Monitor the fuel related parameters with a scan tool.

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

--

Go to Step 20

Go to Symptoms - Engine Controls

10

  1. Turn OFF the ignition.
  2. Remove the vent 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 atmospheric vent.

Is the fuel pressure regulator leaking fuel?

--

Go to Step 25

Go to Step 11

11

  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 and J 37287-100 Fuel Line Shut-Off Quick Connect 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 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 22

Go to Step 12

12

  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. Monitor the fuel pressure gage for 1 minute.

Does the fuel pressure remain constant?

--

Go to Step 25

Go to Step 23

13

Is the fuel pressure more than the specified value?

379 kPa (55 psi)

Go to Step 15

Go to Step 14

14

Is the fuel pressure more than the specified value?

0 kPa (0 psi)

Go to Step 17

Go to Step 20

15

  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 fuel 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. Observe the fuel pressure gage while the fuel pump is operating.

Is the fuel pressure within the specified range?

337-379 kPa (49-55 psi)

Go to Step 24

Go to Step 16

16

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

Did you find and correct the condition?

--

Go to Step 27

Go to Step 25

17

  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 and J 37287-100 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. Monitor 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 increase to more than the specified value?

379 kPa (55 psi)

Go to Step 25

Go to Step 20

18

  1. Remove both fuel tank modules. Refer to Primary Fuel Tank Module Replacement and Secondary Fuel Tank Module Replacement .
  2. Inspect the feed fuel pipe of the siphon jet pump for a restriction.
  3. Inspect the fuel strainer for contaminants.

Did you find and correct the condition?

--

Go to Step 27

Go to Step 19

19

Inspect the fuel return pipe of the siphon jet pump for a restriction.

Did you find and correct the condition?

--

Go to Step 27

Go to Step 26

20

Inspect the following components for a restriction:

    • The fuel filter
    • The fuel feed pipe

Did you find and correct the condition?

--

Go to Step 27

Go to Step 21

21

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 27

Go to Step 22

22
  1. Remove the right fuel tank module. Refer to Primary Fuel Tank Module 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
    • For contaminates in the fuel tank

Did you find and correct the condition?

--

Go to Step 27

Go to Step 26

23
  1. Turn OFF the ignition.
  2. Raise the fuel rail, with the fuel lines connected. Refer to Fuel Injector and Fuel Rail 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 and Fuel Rail Replacement .

Did you complete the replacement?

--

Go to Step 27

--

24

Locate and repair the restricted fuel return pipe.

Did you complete the repair?

--

Go to Step 27

--

25

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 27

--

26

Replace the right fuel tank module. Refer to Primary Fuel Tank Module Replacement .

Did you complete the replacement?

--

Go to Step 27

--

27

Operate the system in order to verify the repair.

Did you correct the condition?

--

System OK

Go to Step 3