GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2005 🢒 Chevy C Cab/Chassis HD (GMT 400) 🢒 Engine 🢒 Engine Controls - 8.1L 🢒 Secondary Fuel System Diagnosis

Circuit Description

Important: If you were not referred to this test from another diagnostic, DO NOT perform this procedure.

The secondary fuel pump is located inside the left frame rail. The fuel pump is powered by a secondary fuel pump relay. Fuel is transferred from the secondary fuel tank to the primary fuel tank in order to ensure all of the usable fuel volume is available to the primary fuel pump. The secondary fuel pump relay supply voltage is received from the primary fuel pump relay when the primary fuel pump is energized. The fuel balance module supplies ground to the secondary fuel pump relay which energizes the secondary fuel pump.

Conditions For Running the Secondary Fuel Pump

Enabling Criteria

    • The primary fuel level sensor resistance goes below 86 ohms and is 9 ohms less than the secondary fuel level sensor.
    • The primary fuel pump is commanded ON.

Disabling Criteria

    • The primary fuel level sensor is 86 ohms or greater.
    • Open fuel level sensors or wiring.
    • The primary fuel level sensor is 8 ohms greater than the secondary fuel level sensor.

Test Description

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

  1. This step verifies the fuel level circuits.

    2.

  2. This step verifies the secondary fuel pump operation.

    3.

  3. This step verifies if voltage is being supplied to the fuel pump.

    4.

  4. This step verifies if ignition voltage is being supplied to the relay.

Step

Action

Values

Yes

No

Schematic Reference: Engine Controls Schematics

1

Did you perform the Diagnostic System Check-Engine Controls?

--

Go to Step 2

Go to Diagnostic System Check - Engine Controls

2

Does the fuel gage indicate over the full mark?

--

Go to Step 10

Go to Step 3

3

  1. Turn OFF the ignition.
  2. Disconnect the fuel balance pump module electrical connector.
  3. Jumper the fuel pump relay control circuit at the control module connector to a good ground.
  4. Turn ON the ignition, with the engine OFF.
  5. Command the primary fuel pump ON with a scan tool.

Does the secondary fuel pump turn ON?

--

Go to Step 6

Go to Step 4

4

  1. Turn OFF the ignition.
  2. Disconnect the fuel balance pump.
  3. Probe the fuel pump supply voltage circuit at the connector with a test lamp connected to a good ground.
  4. Turn On the ignition, with the engine OFF.
  5. Command the primary fuel pump ON with a scan tool.

Does the test lamp illuminate?

--

Go to Step 15

Go to Step 5

5

  1. Turn OFF the ignition.
  2. Disconnect the fuel balance pump control relay.
  3. Turn ON the ignition, with the engine OFF.
  4. Probe the ignition voltage circuit at the relay connector with a test lamp connected to a good ground.

Does the test lamp illuminate?

--

Go to Step 7

Go to Step 17

6
  1. Turn OFF the ignition.
  2. Disconnect fuel feed return pipe at the primary fuel tank.
  3. Place the end of the fuel feed return pipe in an approved gasoline container.
  4. Turn ON the ignition, with the engine OFF.
  5. Command the primary fuel pump ON with a scan tool.

Is fuel flow present?

--

Go to Step 24

Go to Step 12

7
  1. Probe the fuel pump supply voltage circuit, coil side, at the fuel balance pump relay connector with a test lamp connected to a good ground.
  2. Command the primary fuel pump ON with a scan tool.

Does the test lamp illuminate?

--

Go to Step 8

Go to Step 18

8
  1. Ensure that the jumper is still connected to ground at the fuel pump relay control circuit.
  2. Probe the fuel pump relay control circuit at the relay connector (coil side) with a test lamp connected to battery voltage.

Does the test lamp illuminate?

--

Go to Step 9

Go to Step 20

9
  1. Turn OFF the ignition.
  2. Connect a jumper between the ignition voltage circuit and the fuel pump supply circuit of the fuel sender and balance pump control relay.
  3. Turn ON the ignition, with the engine OFF.

Does the fuel balance pump turn ON?

--

Go to Step 13

Go to Step 19

10
  1. Disconnect the fuel balance pump module.
  2. Probe the ignition voltage circuit at the connector with a test lamp connected to a good ground.
  3. Turn ON the ignition, with the engine OFF.

Does the test lamp illuminate?

--

Go to Step 11

Go to Step 17

11

Probe the ground circuit of the fuel balance module at the module harness connector with a test lamp connected to battery voltage.

Does the test lamp illuminate?

--

Go to Step 14

Go to Step 21

12
  1. Inspect the fuel feed pipe between the primary and secondary fuel tanks for leaks or restrictions.
  2. Repair any restrictions or leaks.

Did you find and correct the condition?

--

Go to Step 25

Go to Step 23

13

Test for an intermittent and for a poor connection at the fuel balance 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 25

Go to Step 22

14

Test for an intermittent and for a poor connection at the fuel balance pump module. 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 25

Go to Step 24

15

Test for an intermittent and a poor connection at the secondary fuel pump. 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 25

Go to Step 16

16

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

Did you complete the repair?

--

Go to Step 25

--

17

Repair the open Ignition voltage circuit. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 25

--

18

Repair the open fuel pump supply voltage circuit of the secondary fuel pump relay. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 25

--

19

Repair the open fuel pump supply voltage circuit of the secondary fuel pump. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 25

--

20

Repair the open fuel pump relay control circuit of the fuel balance pump relay. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 25

--

21

Repair the open ground circuit of the fuel balance pump module. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 25

--

22

Replace the fuel balance pump relay. Refer to Relay Replacement in Wiring Systems.

Did you complete the replacement?

--

Go to Step 25

--

23

Replace the fuel balance pump. Refer to Fuel Pump Replacement .

Did you complete the replacement?

--

Go to Step 25

--

24

Replace the fuel balance pump module. Refer to Fuel Sender and Balance Pump Control Module Replacement .

Did you complete the replacement?

--

Go to Step 25

--

25
  1. Reassemble the vehicle as necessary.
  2. Clear any DTCs with a scan tool.
  3. Start the engine.
  4. Operate the vehicle in order to verify the repair.

Did you correct the condition?

--

Go to Step 25

Go to Step 2

26

Observe the Capture Info with a scan tool.

Are there any DTCs that are not diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List

System OK