Case IH 3139 – Engine Control Unit (ECU): Metering Unit Signal Range Check - Signal Too High

The Engine Control Unit (ECU) has detected an abnormally high voltage signal from the Fuel Metering Unit (also known as the Fuel Pressure Control Valve, MPROP, or FCA). This typically points to a short circuit to battery voltage, an open circuit in the wiring harness, or an internal failure (open coil) within the metering unit's solenoid.

• Farmall
• Magnum 235–340 (Series 4)
• Steiger
• JX series
• JX90
• Skid Steer Loaders (SSL)
• Compact Track Loaders (CTL)

1. 1

   Visual Inspection: Inspect the wiring harness and the electrical connector at the Fuel Metering Unit on the high-pressure fuel pump. Look for rubbed-through wires, corrosion, or pushed-out pins.

2. 2

   Circuit Testing: Using a multimeter, test the signal and ground wires between the Engine ECU and the Fuel Metering Unit connector. Specifically, check for a short to battery voltage or an open load.

3. 3

   Component Testing: Measure the resistance across the pins of the Fuel Metering Unit itself to check if the internal solenoid coil is open or shorted.

4. 4

   Secondary Fuel System Checks: Verify that the low-pressure fuel tubes are not clogged (e.g., return from pump to tank) and ensure the fuel pressure sensor is reading accurately, as extreme pressure deviations can sometimes trigger metering unit faults.

1. 1

   Power Down

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

2. 2

   Access the Pump

   Locate the Bosch high-pressure fuel pump (CP3 or similar) on the engine. The Fuel Metering Unit is bolted directly to the side/back of this pump.

3. 3

   Wiring Repair (If Applicable)

   If your diagnostic tests revealed a short to battery or broken wire in the harness, repair the damaged section of the wiring harness and replace the connector pigtail if necessary.

4. 4

   Remove the Metering Unit

   If the wiring is intact and the valve is deemed faulty, disconnect the electrical connector from the Fuel Metering Unit. Remove the mounting screws securing the unit to the high-pressure pump.

5. 5

   Install the New Unit

   Lubricate the O-rings on the new Fuel Metering Unit with clean diesel fuel. Carefully insert the new unit into the pump housing, ensuring the O-rings are not pinched.

6. 6

   Secure and Reconnect

   Tighten the mounting screws to the manufacturer's specified torque. Reconnect the electrical connector until it clicks into place.

7. 7

   Clear Codes and Relearn

   Reconnect the battery. Connect the CNH Electronic Service Tool (EST) to the machine's diagnostic port. Clear the inactive 3139 fault code. Note: If the Engine ECU (EDC) was replaced or flashed during the diagnostic process, you must follow the service tool procedure to restore self-learning parameters.