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Fuel Pump Electrical Circuit Diagnosis




Fuel Pump Electrical Circuit Diagnosis

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.

Circuit/System Description

The circuit opening relay provides ignition positive voltage to the fuel pump. The circuit opening relay is controlled by the powertrain control module (PCM) and receives ignition positive voltage from the EFI relay. The PCM monitors the crank signal circuit for voltage when the ignition switch is in the START (engine cranking) position. When the crank signal circuit indicates the engine is cranking the PCM energizes the circuit opening relay. The PCM also energizes the circuit opening relay whenever starter switch indicates cranking. If the crankshaft position (CKP) signal circuit does NOT indicate cranking, the PCM energizes the circuit opening relay based on starter switch input.

Diagnostic Aids

* If tapping gently on the relay, or wiggling the relay causes a change in the relays operation replace the relay.
* The performance of the relay may be affected by temperature. Test the relay after sitting outside overnight and after running the engine 30 minutes.

Use the following relay cavity table in order to locate the correct cavities to probe during diagnosis. The table layout corresponds to the cavity layout of the relay block.





Reference Information
Schematic Reference

Engine Controls Schematics ([1][2]Electrical Diagrams)
Connector End View Reference

Component Connector End Views (Connector Views)
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)

Description and Operation

Fuel System Description (Fuel System Description)
DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions (Powertrain Diagnostic Trouble Code (DTC) Type Definitions)
Scan Tool Reference

Control Module References (Programming and Relearning) for scan tool information

Circuit/System Testing

1. Ignition OFF, remove the circuit opening relay.
2. Ignition ON, verify that a test lamp illuminates between the relay coil ignition circuit terminal 1 and ground.

• If the test lamp does not illuminate, test the coil ignition circuit for an open/high resistance.

3. Verify that a test lamp illuminates between the relay switch B+ circuit terminal 5 and ground.

• If the test lamp does not illuminate, test the relay switch ignition circuit for a short to ground or an open/high resistance. If the circuit tests normal and the EFI fuse is open, test the relay controlled output circuit terminal 3 for a short to ground. If the circuit tests normal, test or replace the relay.

4. Connect a test lamp between the relay coil control circuit terminal 2 and B+.
5. Command the fuel pump ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.

• If the test lamp is always OFF, test the relay coil control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the PCM.
• If the test lamp is always ON, test the coil control circuit for a short to voltage. If the circuit tests normal, replace the PCM.

6. Connect a 30 A fused jumper between the relay switch B+ circuit terminal 5 and the relay controlled output circuit terminal 3. Verify the fuel pump turns ON.

• If the pump is OFF, test the relay controlled output circuit for an open/high resistance. If the circuit tests normal, test the fuel pump ground circuit for an open/high resistance. If the circuit tests normal, replace the fuel pump.

7. If all circuits test normal, test or replace the circuit opening relay.

Component Testing

1. Ignition OFF, disconnect the circuit opening relay.
2. Test for 85-120 ohm at 20°C (68°F) between terminals 1 and 2.

• If not within the specified range, replace the relay.

3. Test for infinite resistance between the following terminals:

* 5 and 1
* 5 and 2
* 5 and 3
* 1 and 3

• If not the specified range, replace the relay.

4. Install a 20 A fused jumper wire between relay terminal 1 and B+. Install a jumper wire between relay terminal 2 and ground. Test for less than 2 ohm between terminals 5 and 3.

• If greater than the specified range, replace the relay.

Repair Instructions

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

* Fuel Pump and Fuel Filter Assembly Replacement (Fuel Pump and Fuel Filter Assembly Replacement)
* Control Module References (Programming and Relearning) for PCM replacement, setup, and programming

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