GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Pontiac 🢒 2004 🢒 GTO 🢒 Engine 🢒 Engine Controls - 5.7L 🢒 Fuel Pump Electrical Circuit Diagnosis

Circuit Description

When the ignition switch is ON, the powertrain control module (PCM) activates the in-tank fuel pump. The fuel pump remains ON as long as the PCM receives the reference pulses from the ignition system. If there are no reference pulses, the PCM turns the fuel pump OFF after 2-3 seconds. The pump delivers fuel to the fuel rail and injectors. The fuel pressure regulator, located in the fuel tank, maintains the system pressure at 380-410 kPa (55-60 psi). Excess fuel returns to the fuel tank. When the engine is stopped, a scan tool in the output controls function can turn ON the fuel pump.

Incorrect fuel system pressure results in one or many of the following symptoms:

    • Cranks but will not run
    • Cuts out, may feel like an ignition problem
    • Poor fuel economy
    • Loss of power
    • Hesitation
    • DTCs set

Diagnostic Aids

Inspect for the following conditions:

    • Check the electrical resistance of the fuel pump relay. The resistance across the coil side terminals is 95-115 ohms at 20°C (68°F). Measure for infinite resistance across the switch side terminals.
    • The relay electrical contacts may be pitted or sticking. Replace the relay if tapping gently on the relay or wiggling the relay causes a change in the relay's operation.
    • The performance of the fuel pump relay may be affected by temperature. Test the relay after sitting outside overnight and after running the engine 30 minutes.
    • An intermittent malfunction may be caused by fault in the fuel pump electrical circuit. Inspect the wiring harness and the components for an intermittent condition. Refer to Intermittent Conditions .

Use the following relay cavity table in order to locate the correct cavities to probe during diagnosis. The table layout corresponds to the cavity layout of the relay block, with the bottom of the table representing the front of the vehicle.

Relay Cavity Identification

Switch Power

Switch Load

Coil Control, Ignition Voltage

Empty

Coil Ground

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

    3.

  3. This step verifies that the powertrain control module is providing voltage to the fuel pump relay.

    4.

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

    5.

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

    6.

  6. This step determines if the condition is between the fuel pump relay and the body pass through connector.

    7.

  7. This step tests if the relay is causing the condition. Use a fused jumper wire with a 20-ampere fuse.

    8.

  8. This step determines if the condition is between the fuel pump relay and the body pass-through connector.

    9.

  9. This step verifies if the fuel pump ground circuit is causing the condition. Inspect all connections for corrosion or for poor connections.

    10.

  10. A condition with the fuel pump jumper harness can cause the pump to be inoperative. Carefully inspect the fuel pump jumper harness.

    11.

  11. 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

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

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. Refer to Scan Tool Output Controls .

Does the fuel pump turn ON and OFF?

Go to Diagnostic Aids

Go to Step 3

3

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

When you command the fuel pump relay ON and OFF, do you hear a click?

Go to Step 9

Go to Step 4

4

  1. Turn OFF the ignition.
  2. Remove the fuel pump relay from the fuse block-underhood.
  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. Refer to the Relay Cavity Identification table in Diagnostic Aids.
  5. With a scan tool, command the fuel pump relay ON and OFF.

Does the test lamp turn ON and OFF?

Go to Step 5

Go to Step 6

5

  1. Connect a 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 relay 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 for 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 jumper harness from the body pass-through connector.
  2. Test the supply voltage circuit of the fuel pump for a grounded circuit between the fuel pump relay and the body-pass through connector. 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. Remove the fuel tank. Refer to Fuel Tank Replacement .
  2. Inspect the fuel pump jumper harness for the following conditions:
    3. • Damage to the harness
    • A grounded circuit--Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
  3. Replace the 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 battery voltage circuit of the fuel pump relay switch with a test lamp that is connected to a good ground. Refer to the Relay Cavity Identification table in Diagnostic Aids.

Does the test lamp illuminate?

Go to Step 15

Go to Step 25

15

Connect a 20-ampere fused jumper wire between the battery voltage circuit of the fuel pump relay switch and the supply voltage circuit of the fuel pump.

Does the fuel pump operate?

Go to Step 21

Go to Step 16

16

  1. Disconnect the fuel pump jumper harness from the body pass-through connector.
  2. Test the supply voltage circuit of the fuel pump for an open or for high resistance between the fuel pump relay and the body pass through 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, for corrosion on 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 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 jumper harness to the body pass-through connector. 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 19

19
  1. Remove the fuel tank. Refer to Fuel Tank Replacement .
  2. Inspect the fuel pump jumper harness for the following conditions:
    3. • A damaged harness
    • A open circuit--Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
    • A poor connection at the fuel pump connector. 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 26

20

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

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

Did you complete the repair?

Go to Step 29

--

25

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

Did you complete the repair?

Go to Step 29

--

26

Important: Before you replace the fuel pump, inspect for poor connections at the fuel pump, and within the fuel tank.

  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