GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2008 🢒 SLS 🢒 Engine 🢒 Engine Electrical 🢒 Fuel Pump Electrical Circuit Diagnosis

Circuit Description

When the ignition switch is turned ON, the control module energizes the fuel pump relay which applies power to the in-tank fuel pump. The fuel pump relay will remain ON as long as the engine is running or cranking and the control module is receiving reference pulses. If no reference pulses are present, the control module de-energizes the fuel pump relay within 2 seconds after the ignition is turned ON or the engine is stopped.

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.

For an intermittent condition, 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 tests for a grounded voltage supply circuit. The fuel pump fuse supplies power to the fuel pump. Disconnecting the fuel pump in-line harness connector isolates the fuel pump voltage supply circuit.

    4.

  4. This step verifies that the fuel pump fuse is providing voltage to the fuel pump relay.

    5.

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

    6.

  6. 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 - Vehicle?

Go to Step 2

Go to Diagnostic System Check - Vehicle

2

  1. Turn ON the ignition, with the engine OFF.

    2. Important: 

       • Fuel pump DTCs may set when using the Fuel Pump output control.
       • It may be necessary to install a fuel pressure gage to determine if the fuel pump is operating.

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

Does the fuel pump turn ON and OFF?

Go to Diagnostic Aids

Go to Step 3

3

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

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

Go to Step 4

Go to Step 16

4

Turn ON the ignition, with the engine OFF.

Does the fuel pump operate continuously?

Go to Step 5

Go to Step 6

5
  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 17

Go to Step 20

6

Is the fuel pump fuse open?

Go to Step 7

Go to Step 9

7

  1. Disconnect the fuel pump harness inline connector located near the fuel tank.
  2. Test the supply voltage circuit of the fuel pump for a grounded circuit. Refer to Wiring Repairs and Connector Repairs .
  3. Replace the fuel pump fuse if necessary.

Did you find and correct the condition?

Go to Step 21

Go to Step 8

8
  1. Lower the fuel tank if necessary. Refer to Fuel Tank Replacement .
  2. Test or inspect the fuel tank electrical harness for the following conditions:
    3. • Damage to the harness
    • A grounded circuit--Refer to Wiring Repairs and Connector Repairs .
  3. Replace the fuel pump fuse if necessary.

Did you find and correct the condition?

Go to Step 21

Go to Step 15

9

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

Does the test lamp illuminate?

Go to Step 10

Go to Step 18

10

Connect a 15-amp fused jumper wire between the battery positive voltage circuit and the fuel pump supply circuit of the fuel pump relay.

Does the fuel pump operate?

Go to Step 16

Go to Step 11

11

  1. Disconnect the fuel pump harness inline connector located near the fuel tank. Refer to Power and Grounding Component Views .
  2. Test the supply voltage circuit of the fuel pump for an open or for high resistance between the fuel pump relay and the inline connector. Refer to Wiring Repairs and Connector Repairs .

Did you find and correct the condition?

Go to Step 21

Go to Step 12

12

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

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

Did you find and correct the condition?

Go to Step 21

Go to Step 13

13

Inspect for poor connections at the fuel pump inline connector to the body pass through connector. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition?

Go to Step 21

Go to Step 14

14
  1. Lower the fuel tank. Refer to Fuel Tank Replacement .
  2. Test or inspect the fuel tank electrical harness for the following conditions:
    3. • Damage to the harness
    • An open circuit--Refer to Wiring Repairs and Connector Repairs .

Did you find and correct the condition?

Go to Step 21

Go to Step 19

15

  1. Connect all disconnected components.
  2. Install a new fuel pump fuse.
  3. Command the fuel pump ON with a scan tool.

Is the fuel pump fuse open?

Go to Step 19

Go to Diagnostic Aids

16

Inspect for poor connections at the fuel pump relay. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition?

Go to Step 21

Go to Step 20

17

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

Did you complete the repair?

Go to Step 21

--

18

Repair the battery positive voltage circuit of the fuel pump relay for an open. Refer to Wiring Repairs and Connector Repairs .

Did you complete the repair?

Go to Step 21

--

19

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

  1. Replace the fuel tank module. Refer to Primary Fuel Tank Module Replacement .
  2. Replace the fuel pump fuse if necessary.

Did you complete the replacement?

Go to Step 21

--

20

Replace the fuel pump relay.

Did you complete the replacement?

Go to Step 21

--

21

Operate the system in order to verify the repair.

Did you correct the condition?

System OK

Go to Step 2