Case IH 3911 – Engine Control Unit (ECU): Fuel metering unit is shorted to battery voltage at the high side

The control module has detected that the high-side power circuit for the fuel metering unit is receiving unintended, continuous battery voltage. This is typically caused by a wiring harness short, an internal short circuit within the metering unit's solenoid coil, or an overvoltage condition in the machine's electrical system.

• Steiger T4B
• 240 Series Axial-Flow Combines (7240, 8240, 9240)
• A8000 Sugar Cane Harvester
• A8800 Sugar Cane Harvester
• Steiger
• Quadtrac
• Magnum
• Puma
• Maxxum

1. 1

   Check for external power sources (jump-starter, battery charger) connected to the machine that could cause voltage spikes.

2. 2

   Verify system voltage with the engine running to ensure the alternator is not overcharging the system.

3. 3

   Inspect the wiring harness between the Engine ECU and the Fuel Metering Unit for chafed insulation, melted wires, or pinched areas shorting to a 12V/24V source.

4. 4

   Perform a component resistance test by measuring across the pins of the disconnected fuel metering unit (a healthy Bosch solenoid coil typically reads 8 to 11 Ohms; 0 Ohms indicates an internal short).

5. 5

   Perform a harness voltage check with the key ON and the metering unit disconnected to see if battery voltage is present on the control circuit when it should not be.

1. 1

   Repair wiring harness

   If the diagnostic tests point to a wiring harness short, locate the damaged section using the service manual schematics and repair the conductor.

2. 2

   Preparation

   Turn off the machine, remove the key, and disconnect the negative battery cable.

3. 3

   Clean the Area

   Locate the high-pressure fuel pump on the engine. Thoroughly clean the exterior of the pump and the area around the fuel metering unit using brake cleaner and compressed air. Strict cleanliness is required to prevent debris from entering the high-pressure fuel system.

4. 4

   Disconnect

   Unplug the electrical connector from the fuel metering unit.

5. 5

   Removal

   Remove the mounting fasteners (typically three Torx or Allen-head screws) securing the metering unit to the high-pressure pump housing.

6. 6

   Extraction

   Carefully pull the metering unit straight out of the pump housing with a slight twisting motion.

7. 7

   Installation

   Lubricate the O-rings on the new fuel metering unit with clean diesel fuel. Do not use grease or silicone.

8. 8

   Mounting

   Insert the new unit into the pump housing. Install the mounting screws and torque them to the OEM specifications (usually around 5-7 Nm, but verify with your specific engine manual).

9. 9

   Reassembly

   Reconnect the electrical connector and reconnect the battery.

10. 10

    System Reset

    Turn the key to the ON position to allow the electric lift pump to prime the fuel system. Start the engine. Use a diagnostic service tool (like the CNH Electronic Service Tool) to clear the DTC 6455 / 3911 fault code. Note: On some EDC systems, replacing the metering unit requires using the service tool to reset the ECU's self-learning parameters for the fuel valve.