Fuel Pump Electrical Circuit Diagnosis
Fuel Pump Electrical Circuit Diagnosis
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle (Initial Inspection and Diagnostic Overview) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Initial Inspection and Diagnostic Overview) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Initial Inspection and Diagnostic Overview) provides 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 2 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 (MR140 w/o Throttle Actuator Control) (Electrical Diagrams)Engine Controls Schematics (MT34 w/Throttle Actuator Control) (Electrical Diagrams)Engine Controls Schematics (Hatchback) (Electrical Diagrams)
Electrical Information Reference
* Circuit Testing (Component Tests and General Diagnostics)
* Connector Repairs (Component Tests and General Diagnostics)
* Testing for Intermittent Conditions and Poor Connections (Component Tests and General Diagnostics)
* Wiring Repairs (Component Tests and General Diagnostics)
Scan Tool Reference
Control Module References (Programming and Relearning) for scan tool information
Special Tools
J 43244 Relay Puller Pliers
Circuit/System Verification
1. 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.
2. 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, 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. Test for less than 5 ohms of resistance between the relay coil ground circuit terminal 85 and ground.
• If greater than the specified range, repair the relay coil ground circuit for an open/high resistance.
4. Ignition ON, verify a test lamp illuminates between the relay switch B+ voltage circuit terminal 85 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.
5. Install a 15A fused jumper wire between the relay switch B+ voltage circuit terminal 85 and the relay switch supply circuit terminal 87. The fuel pump should turn ON.
• If the fuel pump does not turn ON, test for the following conditions:
* An open/high resistance in the relay switch supply circuit
* An open/high resistance in the fuel pump ground circuit
• If the above circuits test normal, replace the fuel pump.
6. Ignition OFF, connect a test lamp between the relay coil control circuit terminal 86 and ground.
7. Ignition ON, command the fuel pump relay ON and OFF with a scan tool. The test lamp should turn ON and OFF with each command.
• If the test lamp is always ON, test the relay coil control circuit for a short to voltage. If the circuit tests normal, replace the ECM.
• If the test lamp is always OFF, test the relay coil control circuit for a short to ground or an open/high resistance. If circuit tests normal, replace the ECM.
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 ohms of resistance 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 20A fused jumper wire between relay terminal 85 and 12 volts. Install a jumper wire between relay terminal 86 and ground. Test for less than 2 ohms of resistance 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.
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