GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Isuzu 🢒 2006 🢒 Ascender - 2WD 🢒 Engine 🢒 Engine Controls - 6.0L 🢒 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.

Test Description

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

  1. This step determines if the condition is located on the coil side or on the switch side of the fuel pump relay.

    2.

  2. This step verifies that the engine control module (ECM) is providing voltage to the fuel pump relay.

    3.

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

    4.

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

    5.

  5. This step determines if the condition with the circuit is intermittent.

Step

Action

Yes

No

Schematic Reference: Engine Controls Schematics

Connector End View Reference: Engine 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

2

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

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

Go to Step 9

Go to Step 3

3

  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. Refer to Probing Electrical Connectors .
  5. Command the fuel pump relay ON and OFF with a scan tool.

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

Go to Step 4

Go to Step 5

4

  1. Connect a 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 relay ON and OFF with a scan tool.

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

Go to Step 18

Go to Step 21

5

Does the test lamp remain illuminated?

Go to Step 6

Go to Step 7

6

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

Did you find and correct the condition?

Go to Step 27

Go to Step 26

7

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 .

Did you find and correct the condition?

Go to Step 27

Go to Step 19

8

Turn ON the ignition, with the engine OFF.

Does the fuel pump operate continuously?

Go to Step 9

Go to Step 10

9
  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 20

Go to Step 25

10

Inspect the fuel pump fuse.

Is the fuel pump fuse open?

Go to Step 11

Go to Step 13

11
  1. Test the supply voltage circuit of the fuel pump, between the fuel pump fuse and the fuel pump for a short to ground. Refer to Circuit Testing and Wiring Repairs .
  2. Replace the fuel pump fuse if necessary.

Did you find and correct the condition?

Go to Step 27

Go to Step 12

12

  1. Install all removed electrical components.
  2. Install a new fuel pump fuse.
  3. Command the fuel pump relay ON with a scan tool.
  4. Inspect the fuel pump fuse.

Is the fuel pump fuse open?

Go to Step 23

Go to Testing for Intermittent Conditions and Poor Connections

13
  1. Turn OFF the ignition.
  2. Remove 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.

Does the test lamp illuminate?

Go to Step 14

Go to Step 22

14

Connect a 20-amp 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 18

Go to Step 15

15

Test the supply voltage circuit of the fuel pump, between the fuel pump relay and the fuel pump for an open or for high resistance. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

Go to Step 27

Go to Step 16

16

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

Test the ground circuit of the fuel pump for an open or for high resistance. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

Go to Step 27

Go to Step 17

17

Test for an intermittent or for a poor connection at the fuel pump sender assembly connector. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition?

Go to Step 27

Go to Step 23

18

Test for an intermittent or for a poor connection 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 27

Go to Step 25

19

Test for an intermittent and for a poor connection at the harness connector of the engine control module (ECM). Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition?

Go to Step 27

Go to Step 26

20

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

Did you complete the repair?

Go to Step 27

--

21

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

Did you complete the repair?

Go to Step 27

--

22

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

Did you complete the repair?

Go to Step 27

--

23

Test for an intermittent and for a poor connection at the fuel pump sender assembly connector within the fuel tank. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the conditions?

Go to Step 27

Go to Step 24

24
  1. Replace the fuel pump sender assembly. Refer to Fuel Sender Assembly Replacement .
  2. Replace the fuel pump fuse if necessary.

Did you complete the replacement?

Go to Step 27

--

25

Replace the fuel pump relay.

Did you complete the replacement?

Go to Step 27

--

26

Replace the ECM. Refer to Control Module References for replacement, setup, and programming.

Did you complete the replacement?

Go to Step 27

--

27

Operate the system in order to verify the repair.

Did you correct the condition?

System OK

Go to Step 2