GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2005 🢒 STS 🢒 Engine 🢒 Engine Controls - 4.6L (LH2) 🢒 Fuel System Diagnosis

System Description

When you turn the ignition switch to the ON position, the control module 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 control module receives ignition reference pulses. If there are no ignition reference pulses, the control module shuts the fuel pump OFF within 2 seconds after the ignition was switched to the ON position, or if the engine stops.

The fuel tank stores the fuel supply. The fuel pump is an electric pump that is attached to the primary fuel tank module assembly. The fuel pump also supplies fuel to the siphon jet pump, also attached to the primary fuel tank module. The siphon jet pump draws fuel from the secondary side of the fuel tank to the primary 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. A fuel pressure regulator, which is also located in the fuel tank, is attached to the primary fuel tank module. The fuel pressure regulator keeps the fuel available to the fuel injectors at a regulated pressure. Unused fuel is returned from the fuel filter to the fuel tank by a separate fuel return pipe.

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 volts, and the left fuel sender is above 0.8 volts, 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 isolates the condition. Replace the primary fuel tank module assembly, if the fuel pressure remains constant, after closing the valve on the fuel pipe shut-off adapter. Locate and replace the leaking fuel injector if the pressure continues to decrease after closing the valve on the adapter.

    5.

  5. This step isolates the condition. Replace the primary fuel tank module assembly for a stuck open or leaking fuel pressure regulator, if the fuel pressure increases above the specified value.

    6.

  6. 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

Schematic Reference: Fuel Hose/Pipes Routing Diagram

1

Did you perform the Diagnostic System Check - Vehicle?

--

Go to Step 2

Go to Diagnostic System Check - Vehicle

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 right voltage with a scan tool.

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

0.8 V

Go to Step 4

Go to Step 6

4

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 5

Go to Step 14

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 L (5 gal)

Go to Step 15

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?

380-410 kPa (55-60 psi)

Go to Step 7

Go to Step 11

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 19

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 15

Go to Symptoms - Engine Controls

10

  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 appropriate J 37287 Fuel Line Shut-Off Adapters between the fuel feed pipe and the fuel rail inlet.
  5. Open the valve on the fuel feed pipe shut-off adapter.
  6. Command the fuel pump ON with a scan tool.
  7. Bleed the air from the fuel system.
  8. Close the fuel pipe shut-off valve.
  9. Monitor the fuel pressure gage for 1 minute.

Does the fuel pressure remain constant?

--

Go to Step 19

Go to Step 18

11

Is the fuel pressure more than the specified value?

410 kPa (60 psi)

Go to Step 12

Go to Step 13

12

Inspect the fuel return hose/pipe for a restriction.

Did you find and correct the condition?

--

Go to Step 20

Go to Step 19

13

  1. Turn OFF the ignition.
  2. Relieve the fuel system pressure. Refer to Fuel Pressure Relief .
  3. Disconnect the fuel return hose from the fuel return outlet of the fuel filter. Refer to Plastic Collar Quick Connect Fitting Service .
  4. Install the appropriate J 37287 between the return outlet of the fuel filter and the fuel return hose.
  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 gauge.
  10. Slowly close the valve in the fuel 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?

380-410 kPa (55-60 psi)

Go to Step 19

Go to Step 15

14

  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. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .

Did you find and correct the condition?

--

Go to Step 20

Go to Step 19

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 20

Go to Step 16

16

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 .

Did you find and correct the condition?

--

Go to Step 20

Go to Step 17

17
  1. Remove the primary 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 20

Go to Step 19

18
  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 20

--

19

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

Did you complete the replacement?

--

Go to Step 20

--

20

Operate the system in order to verify the repair.

Did you correct the condition?

--

System OK

Go to Step 3