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Home >> Chevy Truck >> 2013 >> Express 3500 V8-6.0L CNG >> Repair and Diagnosis >> Powertrain Management >> Fuel Delivery and Air Induction >> Fuel Pump >> Testing and Inspection

Fuel Pump: Testing and Inspection




Fuel Transfer Pump Diagnosis (LC8\K07\UFP)

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle Diagnostic System Check - Vehicle Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

* Review Strategy Based Diagnosis Strategy Based Diagnosis Strategy Based Diagnosis for an overview of the diagnostic approach.

* Diagnostic Procedure Instructions Diagnostic Procedure Instructions Diagnostic Procedure Instructions provides an overview of each diagnostic category.

Circuit/System Description

The liquid propane control module monitors the two fuel level inputs and determines when the fuel pump - secondary is required to run. The liquid propane control module provides a ground to the control circuit of the fuel pump - secondary relay. With the relay ON voltage is supplied to both the Rear LPG cut-off solenoid valve and the fuel pump - secondary. Fuel is then transferred from the rear three tanks to the front main tank through the supply hose. When the fuel levels are equalized to the calibrated level the liquid propane control module turns OFF the fuel pump - secondary relay.

Diagnostic Aids

* Stuck or skewed fuel level sensors may disable the fuel pump - secondary operation

* A malfunctioning LPG cut-off solenoid valve - secondary may keep fuel from being transferred to the main tank

* A plugged or restricted secondary tank fuel filter may keep fuel from being transferred to the main tank

Reference Information

Description and Operation

Fuel System Description (LC8\K07\UFP) Description and OperationFuel System Description (LC8\FHZ) Description and OperationFuel System Description (LC8\K07\UFM) Description and OperationFuel System Description (Without LC8) Description and Operation

Schematic Reference

Engine Controls Schematics [1][2]Electrical Diagrams

Connector End View Reference

Component Connector End Views 1-2 Shift Solenoid (SS) Valve (M30)

Electrical Information Reference

* Circuit Testing Circuit Testing Circuit Testing

* Connector Repairs Connector Repairs Connector Repairs

* Testing for Intermittent Conditions and Poor Connections Testing for Intermittent Conditions and Poor Connections Testing for Intermittent Conditions and Poor Connections

* Wiring Repairs Wiring Repairs Wiring Repairs

Circuit/System Verification

Note:

* Inspect the fuel system for damage or external leaks before proceeding

* Verify that adequate fuel is in the fuel tanks before proceeding

1. Verify the vehicle starts and runs.

• If the vehicle does not start and run
Refer to Engine Cranks But Does Not Run (Without LC8) Symptom Related Diagnostic ProceduresEngine Cranks But Does Not Run (LC8\KO7) Symptom Related Diagnostic ProceduresEngine Cranks But Does Not Run (LC8\FHZ) Symptom Related Diagnostic Procedures

• If the vehicle starts and runs

2. Verify the fuel gauge is functioning properly

• If the fuel gauge does not function properly
Refer to Fuel Gauge Inaccurate or Inoperative (with LC8 and KO7) Fuel Gauge Inaccurate or Inoperative (with KO7)Fuel Gauge Inaccurate or Inoperative (with LC8 and FHZ) Fuel Gauge Inaccurate or Inoperative (with FHZ)Fuel Gauge Inaccurate or Inoperative (without LC8).

• If the fuel gauge functions properly
Refer to Circuit/System Testing

Circuit/System Testing

1. Remove the fuel pump relay - secondary.

2. Verify the fuel pump - secondary is OFF

• If the fuel pump - secondary is ON
Repair the short to voltage in the fuel pump - secondary supply voltage circuit.

• If the fuel pump - secondary is OFF

3. Connect a test lamp between the B+ circuit terminal E and ground.

4. Verify the test lamp illuminates.

• If the test lamp does not illuminate
Repair the open or high resistance in the circuit

• If the test lamp illuminates

5. Connect a test lamp between the B+ circuit terminal F and ground.

6. Verify the test lamp illuminates.

• If the test lamp does not illuminate
Repair the open or high resistance in the circuit

• If the test lamp illuminates

7. Connect a test lamp between the B+ circuit terminal E and the signal circuit terminal D.

8. Ignition OFF.

9. Verify the test lamp does not illuminate.

• If the test lamp illuminates

1. Disconnect the harness connector at the liquid propane control module.

2. Test for infinite resistance between the signal circuit terminal D and ground.

• If less than infinite resistance, repair the short to ground in the circuit.

• If infinite resistance, test or replace the liquid propane control module.

• If the test lamp does not illuminate

10. Install the fuel pump - secondary relay.

11. Disconnect the harness connector at the liquid propane control module.

Note: Leave the fused jumper connected for step 13-19 unless instructed to remove. If the fuse opens test or replace the fuel pump - secondary relay.

12. Connect a 5 A fused jumper between the fuel pump - secondary relay signal circuit terminal G1 and ground.

13. Verify the fuel pump - secondary relay energizes. You should hear an audible clink.

• If the fuel pump - secondary relay does not energize

1. Disconnect the fused jumper.

2. Test for 2 ohms or less in the signal circuit end to end.

• If greater than 2 ohms, repair the open or high resistance in the circuit.

• If 2 ohms or less, test or replace the fuel pump - secondary relay.

• If the fuel pump - secondary relay energizes

14. Verify the fuel pump - secondary is not active

• If the fuel pump - secondary is active
Test or replace the liquid propane control module.

• If the fuel pump - secondary is not active

15. Disconnect the in-line harness connector at the LPG pump assembly - secondary.

16. Connect a test lamp on the harness side of the in-line between the supply circuit terminal 1 and ground.

17. Verify the test lamp illuminates.

• If the test lamp does not illuminate

1. Disconnect the fused jumper.

2. Test for 2 ohms or less in the supply circuit end to end.

• If greater than 2 ohms, repair the open or high resistance in the circuit.

• If 2 ohms or less, test or replace the fuel pump - secondary relay.

• If the test lamp illuminates

18. Connect a test lamp on the harness side of the in-line between the supply circuit terminal 1 and the ground circuit terminal 2.

19. Verify the test lamp illuminates.

• If the test lamp does not illuminate

1. Disconnect the fused jumper.

2. Test for less than 2 ohms on the ground circuit end to end.

• If 2 ohms or greater , repair the open or high resistance on the circuit.

• If less than 2 ohms, repair the high resistance in the ground connection.

• If the test lamp illuminates

20. Test or replace the LPG pump assembly - secondary.

Repair Instructions

Perform the Diagnostic Repair Verification Verification Tests after completing the repair.

* Relay Replacement (Within an Electrical Center) Relay Replacement (Within an Electrical Center)Relay Replacement (Attached to Wire Harness) Relay Replacement (Attached to Wire Harness)

* LPG Control Module Replacement

* LPG Delivery Module - Secondary Replacement

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