GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2000 🢒 Savana 🢒 Engine 🢒 Engine Controls - 7.4L 🢒 Fuel Pump Electrical Circuit Diagnosis

Refer to Engine Controls Schematics

Cell 23: Fuel Pump Controls


Object Number: 338598 Size: FS
Engine Controls Components
Information Sensors/Switches Description
Cell 23: Fuel Injector Controls
Cell 23: Ignition Controls
OBD II Symbol Description Notice
Cell 10: Battery, AUX A, AUX B, BLOWER, IGN-B, IGN-A, ABS, BATT, LIGHTING, ECM-B, HORN, and A/C Fuses, Inline Fuse 30 A (Gasoline Engines)
Cell 11: ECM-B, HORN, A/C Fuses
Cell 14: G103 (7.4L)
Cell 23: Sensor Controls
VCM Connector End Views
Handling ESD Sensitive Parts Notice
 .

Circuit Description

When the ignition switch is turned ON, the vehicle control module (VCM) turns the in-tank fuel pump ON. The in-tank fuel pump remains ON as long as the engine is cranking or running and the VCM is receiving the distributor reference pulses. If there are no reference pulses, the VCM shuts the fuel pump OFF within 2 seconds after the ignition was turned ON or if the engine stops. The VCM will also turn ON the fuel pump for 2 seconds when the ignition is turned to the OFF position.

Diagnostic Aids

If the fuel pump relay circuit checks out OK, refer to Fuel System Diagnosis .

Excessive fuel may also cause long cranking times which is accompanied by the following conditions:

    • A start that is not as fast as normal
    • A puff of black smoke at the tailpipe

An improperly connected or faulty evaporative emission (EVAP) canister component can cause this problem. Refer to DTC P0440 Evaporative Emission (EVAP) System .

One or more leaking sequential multiport fuel injection (SFI) injectors may also extend the cranking time. Perform the Injector Balance Test. Refer to Fuel Injector Balance Test with Tech 2 .

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 VCM 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. To gain access to the fuel pump connector, the fuel tank may need to be removed. Refer to Fuel Tank Replacement , or Fuel Tank Replacement , or Fuel Tank Replacement .

  7. 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.

    8.

  8. Use the same amperage fuse in the jumper as is used to protect the fuel pump circuit.

    9.

  9. To gain access to the fuel pump connector, the fuel tank may need to be removed. Refer to Fuel Tank Replacement , or Fuel Tank Replacement , or Fuel Tank Replacement .

  10. Inspect the splice pack which contains the fuel pump ground and other ground circuits. Be certain all connections within the splice pack are clean and tight.

Fuel Pump Electrical Diagnosis (wo/Jumper Harness)

Step

Action

Yes

No

1

Did you perform the Powertrain On-Board Diagnostic (OBD) System Check?

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

2

  1. Install a scan tool.
  2. Turn ON the ignition, leaving 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, leaving 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 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 19

Go to Step 22

6

Does the test lamp remain illuminated with each command?

Go to Step 7

Go to Step 8

7
  1. Disconnect the VCM. Refer to VCM Replacement/Programming .
  2. 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 27

Go to Step 26

8
  1. Disconnect the VCM. Refer to VCM Replacement/Programming .
  2. 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 27

Go to Step 20

9

Turn ON the ignition, leaving 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, leaving the engine OFF.

Does the fuel pump operate continuously?

Go to Step 21

Go to Step 25

11

Is the fuel pump fuse open?

Go to Step 12

Go to Step 14

12

  1. Test the supply voltage circuit of the fuel pump for a grounded circuit between the fuel pump fuse and the fuel pump. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
  2. Replace the fuel pump fuse if necessary.

Did you find and correct the condition?

Go to Step 27

Go to Step 13

13

  1. Install all disconnected electrical 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 24

Go to Testing for Electrical Intermittents in Wiring Systems

14
  1. Turn OFF the ignition.
  2. Disconnect the fuel pump relay.
  3. Turn ON the ignition, leaving 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 15

Go to Step 23

15

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 19

Go to Step 16

16

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

Did you find and correct the condition?

Go to Step 27

Go to Step 17

17

Important: Visually and physically 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 high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 27

Go to Step 18

18

Inspect for poor connections at the fuel pump. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 27

Go to Step 24

19

Inspect for poor connections at the fuel pump relay. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 27

Go to Step 25

20

Inspect for poor connections at the harness connector of the VCM. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 27

Go to Step 26

21

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 27

--

22

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

Did you complete the repair?

Go to Step 27

--

23

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 27

--

24

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 27

--

25

Replace the fuel pump relay.

Did you complete the replacement?

Go to Step 27

--

26

Important: The replacement VCM must be programmed.

Replace the VCM. Refer to VCM Replacement/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