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Home >> Chevy Truck >> 2012 >> Express 3500 V8-6.0L >> Repair and Diagnosis >> Powertrain Management >> Fuel Delivery and Air Induction >> Fuel Pump >> Testing and Inspection >> Fuel Pump Electrical Circuit Diagnosis (LC8FHZ)

Fuel Pump Electrical Circuit Diagnosis (LC8FHZ)




Fuel Pump Electrical Circuit Diagnosis (LC8\FHZ)

Diagnostic Instructions

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

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

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

Diagnostic Fault Information






Circuit/System Description

The engine control module (ECM) enables the fuel pump relay when the ignition switch is turned ON. The ECM will disable the fuel pump relay within 4 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 ECM disables the fuel pump relay within 2 seconds if ignition reference pulses cease to be detected and the ignition remains ON.

Diagnostic Aids

The following conditions may cause the fuel pump fuse to open:

* The fuse is faulty.

* There is an intermittent short to ground in the supply voltage circuit of the Compressed Natural Gas (CNG) Control Module.

* The CNG Control Module, CNG Fuel Pressure Regulator or a CNG Tank High Pressure Lock-out Valve Solenoid has an intermittent internal condition.

Reference Information

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

* Connector Repairs Connector Repairs

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

* Wiring Repairs Wiring Repairs

Scan Tool Reference

Control Module References Control Module References for scan tool information

Special Tools

J 43244 Relay Puller Pliers

Circuit/System Verification

Note:
An open or a short to voltage in the control circuit will cause both the Ckt. Open Test Status and the Ckt. Short Volts Test Status parameters to display Fault.

1. Ignition ON.

2. Verify the parameters listed below toggle between OK and Not Run or Not Run and OK when commanding the fuel pump relay ON and OFF with a scan tool.

* Fuel Pump Relay Ckt. Short Gnd Test Status

* Fuel Pump Relay Ckt. Open Test Status

* Fuel Pump Relay Ckt. Short Volts Test Status

• If any parameter does not change

Refer to Circuit/System Testing

• If the parameters change

3. Verify the high pressure lock-out solenoid valves activate when the fuel pump relay is commanded ON with a scan tool.

• If the high pressure lock-out valves do not activate

Refer to Circuit/System Testing

• If the high pressure lock-out valves activate

4. All OK

Circuit/System Testing

1. Ignition OFF and all vehicle systems OFF, it may take up to 2 minutes for all vehicle systems to power down. Disconnect the KR23A fuel pump relay.

2. Test for less than 10 ohms between the fuel pump relay ground circuit and ground.

• If 10 ohms or greater

1. Ignition OFF.

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

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

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

• If less than 10 ohms

3. Ignition ON.

4. Verify a test lamp illuminates between the fuel pump relay B+ circuit and ground.

• If the test lamp does not illuminate and the circuit fuse is OK

1. Ignition OFF.

2. Test for less than 2 ohms in the B+ circuit end to end.

• If 2 ohms of greater, repair the open/high resistance in the circuit.

• If less than 2 ohms, verify the fuse is OK and there is volage at the fuse.

• If the test lamp does not illuminate and the circuit fuse is open

1. Ignition OFF.

2. Test for infinite resistance between the B+ circuit and ground.

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

• If infinite resistance, replace the KR23A fuel pump relay.

• If the test lamp illuminates

5. Verify that a test lamp does not illuminate between the fuel pump relay control circuit and ground.

• If the test lamp illuminates

1. Ignition OFF, disconnect the X1 harness connector at the K20 engine control module, ignition ON.

2. Test for less the 1 V between the control circuit and ground.

• If 1 V or greater, repair the short to voltage on the circuit.

• If less than 1 V, replace the K20 engine control module.

• If the test lamp does not illuminate

6. Remove the test lamp.

7. Verify the Fuel Pump Ckt. Short Gnd. Test Status parameter is OK when commanding the fuel pump relay ON with a scan tool.

• If the Fuel Pump Ckt. Short Gnd. Test Status parameter is not OK

1. Ignition OFF, disconnect the X1 harness connector at the K20 engine control module, ignition ON.

2. Test for less than 2 ohms in the control circuit end to end.

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

• If less than 2 ohms, replace the K20 engine control module.

• If the Fuel Pump Ckt. Short Gnd. Test Status parameter is OK

8. Install a 3 A fused jumper wire between the control circuit and the ground circuit.

9. Verify the scan tool Fuel Pump Ckt. Short Gnd, Test Status parameter is Fault

• If the Fuel Pump Ckt. Short Gnd. Test Status parameter is not Fault

1. Ignition OFF, disconnect the X1 harness connector at the K20 engine control module, ignition ON.

2. Test for less than 2 ohms in the control circuit end to end.

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

• If less than 2 ohms, replace the K20 engine control module.

• If the Fuel Pump Ckt. Short Gnd. Test Status parameter is Fault

10. Verify that a test lamp does not illuminate between the component control circuit and ground.

• If the test lamp illuminates

Repair the short to voltage on the component control circuit.

• If the test lamp does not illuminate

11. Ignition OFF and all vehicle systems OFF, it may take up to 2 minutes for all vehicle systems to power down. Disconnect the X2 harness connector at the CNG control module.

12. Test for less than 10 ohms between the CNG control module ground circuit terminal A and ground.

• If 10 ohms or greater

1. Ignition OFF.

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

• If 2 ohms of greater, repair the open/high resistance in the circuit.

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

• If less than 10 ohms

13. Connect the X2 harness connector at the CNG control module.

14. Ignition ON, connect a 30 A fused jumper wire between the fuel pump relay B+ circuit and the component control circuit.

15. Verify the high pressure lock-out solenoid valves are activated.

• If the high pressure lock-out solenoid valves do not activate

1. Ignition OFF, disconnect the X2 harness connector at the CNG control module.

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

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

• If infinite resistance

3. Test for less than 2 ohms in the component control circuit end to end.

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

• If less than 2 ohms, refer to Fuel System Diagnosis (Without FPCM) Fuel System Diagnosis (Without FPCM)Fuel System Diagnosis (LC8\K07\UFP) Fuel System Diagnosis (LC8K07UFP)Fuel System Diagnosis (LC8\FHZ) Fuel System Diagnosis (LC8FHZ)Fuel System Diagnosis (FPCM) Fuel System Diagnosis (FPCM).

• If the high pressure lock-out solenoid valves activate

4. Test or replace the KR23A fuel pump relay.

Component Testing

1. Ignition OFF, disconnect the KR23A fuel pump relay.

2. Test for 70-110 ohms between terminal 85 and 86.

• If not within the specified range

Replace the KR23A fuel pump relay.

• If between 70-110 ohms

3. Test for infinite resistance between the terminals listed below:

* 30 and 86

* 30 and 87

* 30 and 85

* 85 and 87

• If less than infinite resistance

Replace the relay

• If infinite resistance

4. Connect a 3 A fused jumper wire between relay terminal 86 and B+. Connect a jumper wire between relay terminal 85 and ground. Test for less than 2 ohms between terminals 30 and 87.

• If 2 ohms of greater

Replace the relay

• If less than 2 ohms

5. All OK

Repair Instructions

Perform the Diagnostic Repair Verification Verification Tests after completing the diagnostic procedure.

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

* Control Module References Control Module References for ECM replacement, programming, and setup.

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