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) provide an overview of each diagnostic category.
Diagnostic Fault Information
Circuit/System Description
When you turn ON the ignition switch, the engine control module (ECM) energizes the fuel pump relay which powers the fuel pump ON. The fuel pump remains ON as long as the engine is cranking or running and the ECM receives ignition reference pulses. If there are no ignition reference pulses, the ECM shuts the fuel pump OFF within 3 seconds after the ignition was switched to the ON position or if the engine stops.
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 ([1][2]Electrical Diagrams)
Connector End View Reference
Component Connector End Views (Connector Views)
Description and Operation
Fuel System Description (Fuel System Description)
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 (Programming and Relearning) for scan tool information
Special Tools
J 43244 Relay Puller Pliers
Circuit/System Verification
Ignition ON, command the fuel pump relay ON and OFF with a scan tool. You should hear and feel a click when you command the fuel pump relay ON and OFF.
Circuit/System Testing
1. Ignition OFF, the fuel pump should not be running.
• If the fuel pump runs continuously, test the relay switch supply circuit terminal 87 for a short to voltage. If the circuit tests normal, replace the fuel pump relay.
2. Ignition OFF, remove the fuel pump relay from the electrical center with the J 43244.
3. Verify a test lamp illuminates between the relay ground circuit terminal 85 and B+.
• If the test lamp does not illuminate, repair the ground circuit for an open/high resistance.
4. Ignition ON, test for 2-3 V between the control circuit terminal 86 and ground.
• If less than the specified range, test the control circuit for a short to ground, or an open/high resistance. If the circuit tests normal, replace the ECM.
• If greater than the specified range, test the control circuit for a short to voltage. If the circuit/connections test normal, replace the ECM.
5. Command the fuel pump ON with a scan tool. The DMM should transition from 2-3 V when commanded OFF to greater than 10 V when commanded ON.
• If the circuit voltage does not correspond to the specified values, replace the ECM.
6. Verify a test lamp illuminates between the relay switch B+ voltage circuit terminal 30 and ground.
• If the test lamp does not illuminate, repair the relay switch B+ voltage circuit for a short to ground or an open/high resistance.
7. Install a 15 A fused jumper wire between the relay switch B+ voltage circuit terminal 30 and the relay switch supply circuit terminal 87. The fuel pump should turn ON.
• If the fuel pump does not turn ON, test the relay switch supply circuit and the fuel pump motor ground circuit for an open/high resistance. If the circuits test normal, replace the fuel pump.
8. If all circuits test normal, test or replace the fuel pump relay.
Component Testing
1. Ignition OFF, remove the fuel pump relay from the electrical center with the J 43244.
2. Test for 70-110 ohm between terminals 85 and 86.
• If not within the specified range, replace the 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 relay.
4. Install a 20 A fused jumper wire between relay terminal 85 and 12 V. Install a jumper wire between relay terminal 86 and ground. Test for less than 2 ohm between terminals 30 and 87.
• If greater than the specified range, replace the relay.
Repair Instructions
Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.
* Relay Replacement (Within an Electrical Center) (Service and Repair)
* Fuel Pump Replacement (Locking Ring Type) (Fuel Pump Replacement (Locking Ring Type))
* Control Module References (Programming and Relearning) for ECM replacement, setup, and programming