Case IH 3911 (DTC 6455) - ECU – Engine Control Module (ECM / ECU): Fuel metering unit is shorted to battery voltage at the high side

The Fuel Metering Unit (also known as the Fuel Control Actuator [FCA], M-PROP, or Suction Control Valve) is an electronically controlled solenoid valve mounted on the high-pressure fuel pump. The fault means the control module has detected that the high-side driver circuit supplying power to this actuator is receiving unintended battery voltage, which prevents the module from properly modulating the valve.

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• A8000 Sugar Cane Harvester
• A8800 Sugar Cane Harvester
• Farmall 40
• Farmall 45
• Farmall 50
• Magnum
• Steiger

1. 1

   Visual Inspection: Inspect the wiring harness running from the ECM to the Fuel Metering Unit on the high-pressure fuel pump. Look for chafed insulation, melted wires, or pinch points where the wire might be rubbing against a 12V power source.

2. 2

   Circuit Testing: Disconnect the electrical connector at the Fuel Metering Unit. Using a multimeter, check the high-side driver pin on the harness side for voltage with the key ON. If battery voltage is present when it shouldn't be, the short is in the wiring harness.

3. 3

   Component Testing: Check the internal resistance of the Fuel Metering Unit solenoid. If the internal coil has shorted out, it can cause the ECM to flag a circuit error.

4. 4

   Bypass Test: Unplugging the FCA eliminates metering; on most Bosch CP3 systems, this defaults the pump to maximum rail pressure. If the engine starts (but runs with a loud diesel knock due to max pressure), shut it off immediately. This confirms the mechanical side of the pump is working and the issue is strictly the FCA or its circuit.

1. 1

   Disconnect Power

   Turn off the machine and disconnect the negative battery cable to prevent electrical spikes.

2. 2

   Address Wiring

   If the diagnostic tests revealed a short in the harness, use the OEM service manual wiring diagram to trace the shorted conductor. Repair the damaged wire using weather-sealed connectors or replace the affected harness section.

3. 3

   Remove the Actuator

   If the Fuel Metering Unit itself is internally shorted, locate it on the intake side of the high-pressure fuel pump. Clean the surrounding area thoroughly to prevent dirt from entering the fuel system. Remove the mounting bolts (usually T25 Torx or Allen bolts).

4. 4

   Extract the Unit

   Carefully pull the old actuator out of the pump housing.

5. 5

   Install the New Part

   Lubricate the O-rings on the new Fuel Metering Unit with clean diesel fuel. Gently press it into the pump housing, ensuring the O-rings do not pinch or tear.

6. 6

   Reassembly

   Install and tighten the mounting bolts to the OEM torque specification. Reconnect the electrical harness.

7. 7

   Clear Codes

   Reconnect the battery, turn the key ON, and use a diagnostic scan tool to clear the 3911 (DTC 6455) fault code. Start the engine and verify normal operation.