GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2001 🢒 Eldorado 🢒 Engine 🢒 Engine Controls - 4.6L 🢒 Fuel Pump Electrical Circuit Diagnosis

Circuit Description

When you turn ON the ignition switch, the control module enables the fuel pump relay which powers the fuel pump ON. 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.

Diagnostic Aids

Listen for an audible hiss from the fuel pump when the fuel pump relay is commanded ON. A vibration in the fuel feed line when the fuel pump relay is commanded ON indicates that the fuel pump is operating.

If the condition is intermittent refer to Intermittent Conditions .

Test Description

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

  1. Command both the ON and OFF states. Repeat the commands as necessary.

    2.

  2. This step determines if the condition is located on the coil side or the switch side of the circuit.

    3.

  3. This step verifies that the PCM is providing voltage to the fuel pump relay.

    4.

  4. This step tests for an open in the fuel pump relay ground circuit.

  5. This step determines if a voltage is constantly being applied to the fuel pump relay.

    6.

  6. This tests for a grounded voltage supply circuit. The fuel pump fuse supplies power to fuel pump. Disconnecting the fuel pump in-line harness connector isolates the fuel pump voltage supply circuit.

    7.

  7. This step jumps the fuel pump relay in order to activate the fuel pump.

    8.

  8. This step tests for an open in the fuel pump feed circuit between the in-line connector and the fuel pump relay.

    9.

  9. This step tests for an open or high resistance in the fuel pump ground circuit.

    10.

  10. This step determines if the condition with the circuit is intermittent. If the fuse does not open, inspect the supply voltage circuit between the fuse and the fuel pump for an intermittent condition.

Step

Action

Yes

No

Schematic Reference: Engine Controls Schematics

1

Did you perform the Diagnostic System Check-Engine Controls?

Go to Step 2

Go to Diagnostic System Check - Engine Controls

2

  1. Install a scan tool.
  2. Turn ON the ignition, with the engine OFF.
  3. With a scan tool, command the fuel pump relay ON and OFF.

Does the fuel pump turn ON and OFF?

Go to Intermittent Conditions

Go to Step 3

3

With a scan tool, command the fuel pump relay ON and OFF.

Do you hear a click when you command the fuel pump relay ON and OFF?

Go to Step 9

Go to Step 4

4

  1. Turn OFF the ignition.
  2. Disconnect the fuel pump relay.
  3. Turn ON the ignition, with the engine OFF.
  4. Probe the control circuit of the fuel pump relay with a test lamp that is connected to a good ground.
  5. With a scan tool, command the fuel pump ON and OFF.

Does the test lamp turn ON and OFF?

Go to Step 5

Go to Step 6

5

  1. Connect the test lamp between the control circuit of the fuel pump relay and the ground circuit of the fuel pump relay.
  2. With a scan tool, command the fuel pump ON and OFF.

Does the test lamp turn ON and OFF?

Go to Step 21

Go to Step 24

6

Does the test lamp remain illuminated with each command?

Go to Step 7

Go to Step 8

7

Test the control circuit of the fuel pump relay for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 29

Go to Step 28

8

Test the control circuit of the fuel pump relay for a short to ground or an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 29

Go to Step 22

9

Turn ON the ignition, with the engine OFF.

Does the fuel pump operate continuously?

Go to Step 10

Go to Step 11

10
  1. Turn OFF the ignition.
  2. Disconnect the fuel pump relay.
  3. Turn ON the ignition, with the engine OFF.

Does the fuel pump operate continuously?

Go to Step 23

Go to Step 27

11

Is the fuel pump fuse open?

Go to Step 12

Go to Step 14

12

  1. Disconnect the fuel pump harness in-line connector located near the fuel tank. Refer to Engine Controls Connector End Views .
  2. Test the supply voltage circuit of the fuel pump for a grounded circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
  3. Replace the fuel pump fuse if necessary.

Did you find and correct the condition?

Go to Step 29

Go to Step 13

13
  1. Lower the fuel tank if necessary. Refer to Fuel Tank Replacement .
  2. Test or inspect the fuel tank electrical harness for the following:
    3. • Damage to the harness
    • A grounded circuit--Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
  3. Replace the fuel pump fuse if necessary.

Did you find and correct the condition?

Go to Step 29

Go to Step 20

14
  1. Turn OFF the ignition.
  2. Disconnect the fuel pump relay.
  3. Turn ON the ignition, with the engine OFF.
  4. Probe the switch voltage circuit of the fuel pump relay with a test lamp connected to a good ground.

Does the test lamp illuminate?

Go to Step 15

Go to Step 25

15

Connect a 20-amp fused jumper wire between the switch voltage circuit and the fuel pump supply circuit in the fuel pump cavity.

Does the fuel pump operate?

Go to Step 21

Go to Step 16

16

  1. Disconnect the fuel pump harness in-line connector located near the fuel tank. Refer to Engine Controls Connector End Views .
  2. Test the supply voltage circuit of the fuel pump for an open or high resistance between the fuel pump relay and the in-line connector. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 29

Go to Step 17

17

Important: Inspect the ground circuit for being tight, corrosion on the terminals, or damage to the wiring harness.

Test the ground circuit of the fuel pump for an open or high resistance between the body pass through connector and the ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 29

Go to Step 18

18

Inspect for poor connections at the fuel pump in-line connector to the body pass through connector. Refer to Testing for Intermittent Conditions and Poor Connections and Repairing Connector Terminals in Wiring Systems.

Did you find and correct the condition?

Go to Step 29

Go to Step 19

19
  1. Lower the fuel tank. Refer to Fuel Tank Replacement .
  2. Test or inspect the fuel tank electrical harness for the following:
    3. • Damage to the harness
    • An open circuit--Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 29

Go to Step 26

20

  1. Connect all disconnected components.
  2. Install a new fuel pump fuse.
  3. With a scan tool, command the fuel pump ON.

Is the fuel pump fuse open?

Go to Step 26

Go to Intermittent Conditions

21

Inspect for poor connections at the fuel pump relay. 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 29

Go to Step 27

22

Inspect for poor connections at the harness of the PCM. 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 29

Go to Step 28

23

Repair the supply voltage circuit of the fuel pump for a short to voltage. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 29

--

24

Repair the fuel pump relay ground circuit for an open ground. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 29

--

25

Repair the switch voltage circuit of the fuel pump relay for an open. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 29

--

26

Important: Inspect for poor connections at the fuel pump, and within the fuel tank, before replacing the fuel pump.

  1. Replace the fuel pump. Refer to Fuel Sender Assembly Replacement .
  2. Replace the fuel pump fuse if necessary.

Did you complete the replacement?

Go to Step 29

--

27

Replace the fuel pump relay.

Did you complete the replacement?

Go to Step 29

--

28

Replace the PCM. Refer to Powertrain Control Module Replacement .

Did you complete the replacement?

Go to Step 29

--

29

Operate the system in order to verify the repair.

Did you correct the condition?

System OK

Go to Step 2