GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 1999 🢒 Catera 🢒 Body and Accessories 🢒 Wiring Systems 🢒 Fuel System Diagnosis

Circuit Description

When the ignition is turned ON, the electronic control module (ECM) compares the engine coolant temperature to an internal clock to determine if a fuel pump prime is required. When the ECM calculates that a fuel prime is necessary, the fuel pump relay will be turned on for 2 seconds. The pump remains ON as long as the engine is cranking or running and the ECM is receiving reference pulses. If there are no reference pulses, the ECM shuts the fuel pump OFF within 2 seconds after the ignition is switched off. If the ECM calculations indicate that the fuel system still has adequate residual pressure, a prime will not occur.

An electric fuel pump supplies the fuel through an in-line filter to the fuel rail and injectors. The pump is attached to the fuel sender assembly inside of the fuel tank. The pump is designed to provide fuel pressure above what is needed by the fuel injectors. The pressure regulator keeps the fuel available to the injectors at a regulated pressure. Unused fuel is returned to the fuel tank by the fuel return pipe. The fuel system does not adjust fuel pressure to compensate for manifold vacuum. The port on the fuel pressure regulator is an atmospheric vent only. This port is connected to the bottom of the throttle body and vented in front of the throttle plates.

Test Description

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

  1. With the ignition ON and the fuel pump running, the fuel pressure that is indicated by the fuel pressure gauge should be 275-313 kPa (40-46 psi). This pressure is controlled by spring pressure inside of the fuel pressure regulator.

    2.

  2. A fuel system that cannot maintain a constant fuel pressure has a leak in one or more of the following areas:

    3. • The fuel pump check valve
    • The valve or valve seat within the fuel pressure regulator
    • The fuel injectors
    • The fuel feed line
    • The fuel feed line in the fuel tank

  3. Fuel pressure which drops off during acceleration, cruise, or hard cornering may set a DTC P1460 if the fuel level is low it may also cause a lean condition. A lean condition can cause a loss of power, surging, or misfire. Diagnose a lean condition using a scan tool.

    4.

  4. A rich condition may result from the fuel pressure being above 313 kPa (46 psi). A rich condition may cause DTC P0172 or DTC P0175 to set. Driveability conditions associated with rich conditions can include hard starting, followed by black smoke, and a strong sulfur smell in the exhaust.

    A lean condition may result from the fuel pressure being below 275 kPa (40 psi). A lean condition may cause DTC P0171 or DTC P0174 to set. Driveability conditions associated with lean conditions can include hard starting, when the engine is cold, hesitation, poor driveability, lack of power, surging, and misfiring.

    5.

  5. Restricting the fuel return line with the J 37287 fuel line shut-off adaptor causes the fuel pressure to rise above the regulated fuel pressure. With the fuel pump enabled using a scan tool, the fuel pressure should rise above 313 kPa (46 psi) as the valve on the fuel line shut-off adaptor connected to the fuel return line becomes partially closed.

  6. If the fuel pressure regulator is leaking fuel internally there will be signs of fuel at this connection. The hose that is connected to the fuel pressure regulator does NOT have vacuum applied to it. This is an ATMOSPHERIC VENT ONLY. It is connected to the bottom of the throttle body and is vented in front of the throttle plates.

Fuel System Diagnosis

Step

Action

Values

Yes

No

1

Did you perform the Powertrain On-Board Diagnostic (OBD) System Check?

--

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

2

  1. Turn OFF the ignition.
  2. Turn OFF all the accessories.

    3. Caution: Wrap a shop towel around the fuel pressure connection in order to reduce the risk of fire and personal injury. The towel will absorb any fuel leakage that occurs during the connection of the fuel pressure gage. Place the towel in an approved container when the connection of the fuel pressure gage is complete.

  3. Install the J 34730-1A fuel pressure gauge using the J 42242 fuel pressure gauge adapter.
  4. Place the bleed hose of the fuel pressure gauge into an approved gasoline container.
  5. Turn ON the ignition.
  6. Using the scan tool command the fuel pump ON.
  7. Bleed the air out of the fuel pressure gauge.

Is the fuel pressure within the specified limits with the pump running?

275-313 kPa (40-46 psi)

Go to Step 3

Go to Step 10

3

Using the scan tool, command the fuel pump OFF. After the pump stops, does the fuel pressure stabilize and hold steady within the specified range?

240-275 kPA (35-40 psi)

Go to Step 4

Go to Step 7

4

Is the fuel pressure suspected of dropping-off during acceleration, cruise, or hard cornering?

--

Go to Step 5

Go to Step 23

5

Visually and physically inspect the following items for a restriction:

    • The in-line fuel filter
    • The fuel feed line

Did you find and correct the condition?

--

Go to Step 23

Go to Step 6

6
  1. Remove the fuel sender assembly, refer to Fuel Sender Assembly Replacement .
  2. Visually and physically inspect the following items:
    3. • The fuel pump strainer for a restriction
    • Broken baffles inside the fuel tank

Did you find and correct the condition?

--

Go to Step 23

Go to Step 20

7
  1. Relieve the fuel pressure. Refer to Fuel Pressure Relief .
  2. Disconnect the fuel feed line and the fuel return line from the fuel rail.
  3. Install the J 37287 fuel line shut-off adaptors using the J 37287-100 fuel line shut-off quick connect adapters between the fuel feed line and the fuel return line at the fuel rail.
  4. Open the valves on the fuel line shut-off adaptors.
  5. Turn ON the ignition.
  6. Turn ON the fuel pump with the scan tool.
  7. Place the bleed hose of the fuel pressure gauge into an approved gasoline container.
  8. Bleed the air out of the fuel pressure gauge.
  9. Wait for the fuel pressure to build.
  10. Use the scan tool in order to turn OFF the fuel pump.
  11. Close the valve in the fuel line shut-off adaptor that is connected to the fuel feed line.

Does the fuel pressure stabilize and remain constant?

--

Go to Step 8

Go to Step 9

8

Visually and physically inspect the fuel feed line for leaks.

Did you find and correct the condition?

--

Go to Step 23

Go to Step 17

9
  1. Open the valve in the fuel line shut-off adaptor that connects to the fuel feed line.
  2. Turn ON the fuel pump with the scan tool.
  3. Wait for the fuel pressure to build.
  4. Turn OFF the fuel pump with the scan tool.
  5. Close the valve in the fuel line shut-off adaptor that connects to the fuel return line.

Does the fuel pressure stabilize and remain constant?

--

Go to Step 21

Go to Step 18

10

Is the fuel pressure above the specified limit?

313 kPa (46 psi)

Go to Step 11

Go to Step 13

11
  1. Relieve the fuel pressure. Refer to Fuel Pressure Relief .
  2. Disconnect the fuel return line from the fuel rail.
  3. Install the J 37287-100 fuel line shut-off quick connect adapters to the fuel return side of the fuel rail.
  4. Attach a length of flexible fuel hose to fuel line shut-off quick connect adapters off the fuel rail return outlet passage.
  5. Place the open end of the flexible fuel hose into an approved gasoline container.
  6. Turn ON the fuel pump with the scan tool.

Is the fuel pressure within the specified limits?

275-313 kPa (40-46 psi)

Go to Step 22

Go to Step 12

12

Visually and physically inspect the fuel rail outlet passage for a restriction.

Did you find and correct the condition?

--

Go to Step 23

Go to Step 21

13

Is the fuel pressure above the specified value?

0 kPa (0 psi)

Go to Step 14

Go to Step 15

14

  1. Relieve the fuel pressure. Refer to Fuel Pressure Relief .
  2. Disconnect the fuel return line from the fuel rail.
  3. Install the J 37287 fuel line shut-off adaptor using the J 37287-100 fuel line shut-off quick connect adapters between the fuel return line and the fuel rail.
  4. Open the valve on the fuel line shut-off adaptor.
  5. Turn ON the ignition.
  6. Turn ON the fuel pump with the scan tool.
  7. Place the bleed hose of the fuel pressure gauge into an approved gasoline container.
  8. Bleed the air out of the fuel pressure gauge.

    9. Notice: Do Not allow the fuel pressure to exceed 483 kPa (70 psi). Fuel pressure in excess of 483 kPa (70 psi) may damage the fuel pressure regulator.

  9. Slowly close the valve in the fuel line shut-off adaptor that connects to the fuel return line while observing the fuel pressure.

Does the fuel pressure rise above the specified value?

407 kPa (59 psi)

Go to Step 21

Go to Step 16

15
  1. Turn ON the fuel pump with the scan tool.
  2. Listen for audible fuel pump operation.

Does the fuel pump operate?

--

Go to Step 16

Go to Fuel Pump Circuit Diagnosis

16

Visually and physically inspect the following items:

    • The in-line fuel filter for obstructions
    • The fuel feed line for leaks

Did you find and correct the condition?

--

Go to Step 23

Go to Step 17

17

Remove the fuel sender assembly in order to inspect the following items, refer to Fuel Sender Assembly Replacement :

    • The fuel feed line for a restriction
    • The fuel feed line in the tank for leaks
    • Verify that the fuel pump is the correct pump for the vehicle
    • The fuel pump electrical wiring for high resistance
    • An inoperative fuel pump

Did you find and correct the condition?

--

Go to Step 23

Go to Step 20

18

Important: The hose that is connected to the fuel pressure regulator is an atmospheric vent only. There is NO compensation for manifold vacuum on the fuel pressure.

  1. Remove the atmospheric vent hose from under the throttle body.
  2. Turn ON the fuel pump using the scan tool.
  3. Inspect the atmospheric vent hose for signs of fuel leakage while the pump is running.

Does the atmospheric vent hose show signs of fuel leakage coming from the fuel pressure regulator?

--

Go to Step 21

Go to Step 19

19
  1. Remove the intake plenum. Refer to Intake Plenum Replacement in Engine Mechanical.
  2. Remove the intake manifold. Refer to Intake Manifold Replacement in Engine Mechanical.
  3. Re-attach the fuel rail, injectors and supply and return lines to the intake manifold using the fuel rail attaching bolts.
  4. Pressurize the fuel system using the scan tool.
  5. Visually inspect the fuel injector nozzles for leaks.
  6. Replace any leaking injectors. Refer to Fuel Injector and Fuel Rail Replacement .

Did you complete the action?

--

Go to Step 23

--

20

Replace the fuel pump. Refer to Fuel Pump Replacement .

Is the action complete?

--

Go to Step 23

--

21

Replace the fuel pressure regulator, refer to Fuel Pressure Regulator Replacement .

Is the action complete?

--

Go to Step 23

--

22

Locate and correct the restriction in the fuel return line.

Is the action complete?

--

Go to Step 23

--

23

Use the scan tool in order to display the Capture Information and the Review Capture Information function.

Are there any DTCs displayed that have not been diagnosed?

--

Go to the applicable DTC table

System OK