Case IH 3912 (DTC 7555) - ECU – Engine Control Module (ECM / ECU): Fuel metering unit is shorted to ground at the high side.

The Fuel Metering Unit (also known as the MPROP, Fuel Measuring Unit, or Fuel Pressure Control Valve) is a pulse-width modulated solenoid valve located on the high-pressure fuel pump. It regulates the amount of fuel allowed into the high-pressure pumping chambers. A "short to ground at the high side" means the control module has detected that the power supply circuit (high side) to this solenoid is shorted directly to a ground source. This prevents the valve from operating, typically resulting in a severe loss of engine power, engine stalling, or a forced idle state.

• MAXXUM T4E
• 240 Series Axial-Flow Combines (7230, 8230, 9230)
• Puma series
• Magnum series (MX210, MX230, MX255, MX285)
• Farmall series (40, 45, 50)
• A8000 and A8800 Sugar Cane Harvesters

1. 1

   Visually inspect the wiring harness running from the ECM to the fuel metering unit for chafed insulation, pinched wires, or areas rubbing against the engine block or frame

2. 2

   Perform a harness short-to-ground test (wiring cause): Disconnect the electrical connector at the fuel metering unit and the ECM, then check for continuity between the high-side supply pin on the harness connector and a known good chassis ground

3. 3

   Perform a component resistance test (internal component cause): Test the resistance across the pins of the fuel metering unit and test for continuity between the unit's high-side pin and its metal housing to identify an internal short

1. 1

   Isolate the Short

   Based on the diagnostic tests, determine if the short is in the machine's wiring harness or internal to the fuel metering unit.

2. 2

   Repair the Harness (If Applicable)

   If the harness is shorted, locate the damaged section of the conductor. Splice and repair the wire using OEM-approved heat-shrink connectors, or replace that section of the engine harness.

3. 3

   Replace the Fuel Metering Unit (If Applicable)

   If the wiring tests perfectly but the code persists or the unit is internally shorted: Thoroughly clean the area around the high-pressure fuel pump to prevent debris from entering the fuel system. Disconnect the electrical connector to the metering unit. Remove the mounting screws securing the metering unit to the high-pressure fuel pump. Carefully extract the unit. Lubricate the O-rings on the new fuel metering unit with clean diesel fuel or approved assembly grease. Install the new unit and torque the mounting screws to the manufacturer's specification.

4. 4

   Clear Codes and Test

   Reconnect all electrical connections. Turn the key on and use a diagnostic scan tool to clear the inactive 3912 / 7555 fault code. Start the engine and verify that the fuel rail pressure is within specification and the code does not return.