Fuel Pump Electrical Circuit Diagnosis
Fuel Pump Electrical Circuit Diagnosis
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Initial Inspection and Diagnostic Overview
* Review Strategy Based Diagnosis for an overview of the diagnostic approach.
* 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.
Special Tools
J 43244 Relay Puller Pliers
Circuit/System Verification
Important: 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.
Ignition ON, command the fuel pump relay ON and OFF with a scan tool while observing the following control circuit status parameters:
* Fuel Pump Relay Ckt. Short Gnd Test Status
* Fuel Pump Relay Ckt. Open Test Status
* Fuel Pump Relay Ckt. Short Volts Test Status
Each parameter should toggle between OK and Not Run or Not Run and OK.
Circuit/System Testing
1. Ignition OFF, disconnect the fuel pump relay.
2. Ignition ON, verify that a test lamp illuminates between the ground circuit terminal and B+.
^ If the test lamp does not illuminate, test the ground circuit for a short to voltage or an open/high resistance.
3. Verify that a test lamp does not illuminate between the ground circuit terminal and the control circuit terminal.
^ If the test lamp illuminates, test the control circuit for a short to voltage. If the circuit tests normal, replace the ECM.
4. Remove the test lamp.
5. Command the fuel pump relay ON with a scan tool. Verify the scan tool fuel pump relay Ckt. Short Grnd Test Status parameter is OK.
^ If not the specified value, test the fuel pump relay control circuit for a short to ground. If the circuit tests normal, replace the ECM.
6. Install a 3A fused jumper wire between the fuel pump relay control circuit terminal and the ground circuit terminal. Command the fuel pump ON with a scan tool. Verify the scan tool fuel pump relay Ckt. Short Grnd Test Status parameter is Fault.
^ If not the specified value, test the fuel pump relay control circuit for an open/high resistance. If the circuit tests normal, replace the ECM.
7. Inspect the fuel pump fuse.
^ If the fuel pump fuse is open, test for the following conditions:
* A short to ground in the relay switch B+ circuit
* A short to ground in the supply voltage circuit of the fuel pump
^ If the above circuits test normal, replace the fuel tank module.
8. Verify that a test light illuminates between the B+ circuit and ground.
^ If the test lamp does not illuminate, test the B+ circuit for an open/high resistance.
9. Connect a 15 A fused jumper wire between the B+ circuit and the supply voltage circuit of the fuel pump. Verify the fuel pup is activated.
^ If the fuel pump does not activate, test for the following conditions:
* An open/high resistance in the supply voltage circuit of the fuel pump
* An open/high resistance in the ground circuit of the fuel pump
^ If the above circuits test normal, replace the fuel tank module.
10. If all circuits test normal, test or replace the fuel pump relay.
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure. Verification Tests
* Fuel Sender Assembly Replacement
* Relay Replacement (Attached to Wire Harness) Relay Replacement (Within an Electrical Center)