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Fuel Pump Electrical Circuit Diagnosis (Without FPCM)




Fuel Pump Electrical Circuit Diagnosis (Without FPCM)

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 2 seconds unless the ECM detects ignition reference pulses. The ECM 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 fuel pump.

* The fuel pump has an intermittent internal condition.

Reference Information

Schematic Reference

Engine Controls Schematics (except L96) [1][2]Electrical DiagramsEngine Controls Schematics (L96) [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

* CH-48027 Digital Pressure Gauge

Circuit/System Verification

1. Ignition ON, observe the DTC information with a scan tool. DTC P0628 and P0629 should not set.

• If a DTC sets, refer to Diagnostic Trouble Code (DTC) List - Vehicle Diagnostic Trouble Code (DTC) List - Vehicle

2. Ignition ON, command the Fuel Pump Relay ON with a scan tool. You should hear the fuel pump operate for 2-3 s and then turn OFF.

3. Ignition OFF, install a CH-48027. Refer to Fuel Pressure Gauge Installation and Removal Testing and Inspection.

4. Ignition ON, command the fuel pump ON with a scan tool. The fuel pressure should be between 345-414 kPa (50-60 psi).

5. Operate the vehicle within the Conditions for Running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.

Circuit/System Testing

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

2. Ignition ON, verify that a test lamp illuminates between the B+ circuit terminal 30 and ground.

• If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.

3. Verify that a test lamp does not illuminate between the component control circuit terminal 87 and ground.

• If the test lamp illuminates, test the component control circuit for a short to voltage.

4. Ignition OFF, disconnect the harness connector at the fuel tank sending unit.

5. Ignition OFF and all vehicle systems OFF. It may take up to 2 minutes for all vehicle systems to power down. Test for less than 10 ohms between the fuel pump ground circuit terminal A and ground.

• If greater than the specified range, test the ground circuit for an open/high resistance.

6. Connect the harness connector at the fuel tank sending unit.

7. Ignition ON, connect a 25 A fused jumper wire between the B+ circuit terminal 30 and the component control circuit terminal 87. Verify the fuel pump is activated.

• If the fuel pump does not activate, test the component control circuit for an open/high resistance. If the circuit tests normal, test or replace the fuel tank fuel pump module.

8. If all circuit test normal, 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.

3. Test for infinite resistance between the following terminals:

* 30 and 86

* 30 and 87

* 30 and 85

* 85 and 87

• If not the specified value, replace the KR23A fuel pump relay.

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 greater than the specified range, replace the KR23A fuel pump relay.

Repair Instructions

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

* Fuel Tank Fuel Pump Module Replacement (15 Reg Cab With 26 Gal Tank) Service and RepairFuel Tank Fuel Pump Module Replacement (25/35 Series) Service and RepairFuel Tank Fuel Pump Module Replacement (15 Ext/Crew Cab With 26 Gal Tank) Service and RepairFuel Tank Fuel Pump Module Replacement (15 Reg/Ext/Crew Cab w/34 Gal Tank) Service and 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)

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

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