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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 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 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.

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. If the vehicle passes the Circuit/System Verification test, then operate the vehicle within the conditions for running the DTC. You may also operate the vehicle within the conditions that are captured in the Freeze Frame/Failure Records List.

Circuit/System Testing

1. Ignition OFF, the fuel pump should not be operating.

• If the fuel pump operates continuously, test for a short to voltage in the fuel pump supply voltage circuit. If the circuit/connections test 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 ground circuit of the fuel pump relay coil and ground.

• If greater than 5 ohms, repair the ground circuit of the fuel pump relay coil for an open/high resistance.

4. Ignition ON, verify a test lamp illuminates between the ignition 1 voltage circuit of the fuel pump relay and ground.

• If the test lamp does not illuminate, repair the ignition 1 voltage circuit of the fuel pump relay for a short to ground or an open/high resistance.

5. Connect a 15A fused jumper wire between the ignition 1 voltage circuit of the fuel pump relay and the supply voltage circuit of the fuel pump. The fuel pump should operate.

• If the fuel pump does not operate, test for the following conditions:

* An open/high resistance in the motor circuit of the fuel pump
* An open/high resistance in the ground circuit of the fuel pump

• If the above circuit/connections test normal, replace the fuel pump.

6. Ignition OFF, connect a test lamp between the control circuit of the fuel pump relay 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 remains ON all the time, test for a short to voltage on the control circuit. If the circuit/connections test normal, replace the ECM.

• If the test lamp remains OFF all the time, test for a short to ground or an open/high resistance on the control circuit. If circuit/connections test normal, replace the ECM.

8. If all circuit/connections test normal, test or replace the fuel pump relay.

Component Testing

1. Measure for 70-110 ohms of resistance between terminals 85 and 86 of the fuel pump relay.

• If the resistance is not within the specified range, replace the fuel pump relay.

2. Measure for infinite resistance between the following terminals of the fuel pump relay:

* 30 and 86
* 30 and 87
* 30 and 85
* 85 and 87

• If continuity is detected, replace the fuel pump relay.

3. Connect a 20A fused jumper wire from the positive terminal of the battery to relay terminal 85. Connect a jumper wire from the negative terminal of the battery to relay terminal 86. Measure for less than 2 ohms between terminals 30 and 87 of the relay.

• If the resistance measures greater than 2 ohms, replace the fuel pump relay.

Repair Instructions

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

Fuel Sender Assembly Replacement

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