CM871 and CM876 Electronic Control Systems, ISX and ISM Engines – 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
• wire insulation damage
• connector shell broken
• damaged locking tab connector.

For general inspection techniques, refer to Component Connector and Pin Inspection, Procedure 019-361.

Refer to Procedure 019-043 for the proper procedure for replacing or repairing connectors, pins, or harness.

CAUTION  Do not use probes or leads other than Part Number 3822758 and Part Number 3822917. The connector will be damaged. The leads must fit tightly in the connector without expanding the pins in the connector.

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 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 then repair or replace the engine harness.

CAUTION  Do not use probes or leads other than Part Number 3164572. The connector will be damaged. The leads must fit tightly in the connector without expanding the pins in the connector.

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.

There 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. Using a multimeter, 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 not, replace the fuel lift pump relay.

CAUTION  Do not use probes or leads other than Part Number 3822758 and Part Number 3822917. The connector will be damaged. The leads must fit tightly in the connector without expanding the pins in the connector.

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 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.

Using a multimeter, 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 or contact your local Cummins Authorized Dealer.

Check the fuel lift pump relay for proper operation.

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

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

With the keyswitch on, 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 ECM for the proper calibration and contact the local Cummins Authorized Dealer.

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. If the lift pump does not operate when using the jumper wire, then refer to Procedure 019-396 for replacing the lift pump.