GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2005 🢒 DeVille 🢒 Engine 🢒 Engine Electrical 🢒 Fuel Pump Electrical Circuit Diagnosis

Circuit Description

The control module enables the fuel pump relay when the ignition switch is turned ON. The control module will disable the fuel pump relay within two seconds unless the control module detects ignition reference pulses. The control module continues to enable the fuel pump relay as long as ignition reference pulses are detected. The control module disables the fuel pump relay within two seconds if ignition reference pulses cease to be detected and the ignition remains ON.

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.

Fuel Pump Electrical Circuit Diagnostic

Step

Action

Yes

No

Schematic Reference: Engine Controls Schematics

Connector End View Reference: Powertrain Control Module Connector End Views or Engine Controls Connector End Views

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. Install a scan tool.
  2. Turn ON the ignition, with the Engine OFF.
  3. Command the fuel pump relay ON and OFF with a scan tool.

Does the fuel pump turn ON and OFF?

Go to Intermittent Conditions

Go to Step 3

3

Command the fuel pump relay ON and OFF with a scan tool.

Does the fuel pump relay turn ON and OFF when commanded with a scan tool?

Go to Step 9

Go to Step 4

4

  1. Turn OFF the ignition.
  2. Remove 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. Command the fuel pump ON and OFF with a scan tool.

Does the test lamp turn ON and OFF when commanded with a scan tool?

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. Command the fuel pump ON and OFF with a scan tool.

Does the test lamp turn ON and OFF when commanded with a scan tool?

Go to Step 21

Go to Step 24

6

Does the test lamp remain illuminated?

Go to Step 7

Go to Step 8

7

Test the fuel pump relay control circuit 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 fuel pump relay control circuit 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. Remove 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 Inline Harness Connector End Views in Wiring Systems.
  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. Remove 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 Inline Harness Connector End Views in Wiring Systems.
  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

Test for an intermittent and a poor connection 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.

Does the fuel pump fuse open?

Go to Step 26

Go to Intermittent Conditions

21

Test for an intermittent and a poor connection 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

Test for an intermittent and a poor connection at the harness of the powertrain control module (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 short to voltage in the fuel pump supply voltage circuit. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 29

--

24

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

Did you complete the repair?

Go to Step 29

--

25

Repair the open in the fuel pump relay switch voltage circuit. 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, 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 Control Module References in Computer/Integrating Systems for replacement, setup, and programming.

Did you complete the replacement?

Go to Step 29

--

29

Operate the vehicle in order to verify the repair.

Did you correct the condition?

System OK

Go to Step 2