Cummins ISX11.9 CM2250 – Service Manual 019-397   Fuel Lift Pump Circuit

Inspect the engine harness, lift pump power connector, lift pump relay power connector, and the lift pump relay pins for the following:

• Loose connector
• Corroded pins
• Bent or broken pins
• Pushed back or expanded pins
• Moisture in or on the connector
• Missing or damaged connector seals
• Dirt or debris in or on the connector pins
• Connector shell broken
• Wire insulation damage
• Damaged locking tab connector.

Use the following procedure for general inspection techniques. Refer to Procedure 019-361 in Section 19.

Use the following procedure for the proper replacement or repair of connectors, pins, or harness. Refer to Procedure 019-043 in Section 19.

Check for an open circuit in the fuel lift pump return circuit. Disconnect the 2-pin fuel lift pump power connector at the fuel lift pump.

Disconnect the fuel lift pump relay power connector where the original equipment manufacturer (OEM) harness connects to the engine harness.

Measure the resistance of the fuel lift pump return between these two connectors.

The resistance must be 10 ohms or less. If the resistance is greater than 10 ohms, repair or replace the engine harness.

Check for an open circuit in the fuel lift pump relay return line.

Measure the resistance from the fuel lift pump relay return pin, in the engine harness relay connector, to engine block ground.

The resistance must be 10 ohms or less. If the resistance is greater than 10 ohms, repair or replace the engine harness ground.

Measure the resistance of the fuel lift pump relay.

Use a multimeter to measure the resistance between the fuel lift pump relay signal pin and the fuel lift pump relay return pin on the relay.

The resistance must be between 70 and 80 ohms. If the resistance is not between 70 and 80 ohms, replace the fuel lift pump relay.

Remove the fuel lift pump power connector at the fuel lift pump.

Insert a test lead into the fuel lift pump supply pin and another test lead into the fuel lift pump return pin on the harness connector. Turn the keyswitch ON and measure the voltage with a multimeter.

The voltage must be battery voltage. If voltage is not present, check the fuse on the fuel lift pump relay supply line. Replace the fuse, if necessary.

If voltage is not correct, disconnect the 2-pin connector between the OEM harness and the engine harness that supplies the fuel lift pump relay with unswitched battery power.

Use a multimeter to measure the voltage at the 2-pin connector on the OEM harness. The voltage must be battery voltage. If voltage is not present, repair or replace the OEM wiring harness.

Check the fuel lift pump relay for proper operation.

Unplug the fuel lift pump relay from the engine harness connector.

Measure the voltage at the fuel lift pump relay supply pin. The voltage must be battery voltage. If voltage is not present, check fuses, OEM harness, and engine harness for shorts and open circuits.

Turn the keyswitch ON and measure the voltage at the fuel lift pump relay signal pin on the engine harness relay connector. A measurement of 12-VDC must be indicated. If 12-VDC is not indicated, check the electronic control module (ECM) for the proper calibration. Contact a Cummins® Authorized Repair Location.

Unplug the fuel lift pump relay from the engine harness connector.

Connect the 2-pin fuel lift pump power connector to the fuel lift pump.

Insert a jumper wire between the fuel lift pump relay supply pin and the fuel lift pump supply pin in the engine harness relay connector. If the fuel lift pump is functioning correctly, the fuel lift pump will run. Use the following procedure to replace the fuel lift pump if the lift pump does not operate when using the jumper wire. Refer to Procedure 005-045 in Section 5.