New Holland NH 3104 – Engine Control Unit (ECU / ECM): Fuel pressure signal - SOURCE HIGH

The Engine Control Module (ECM) is detecting a voltage signal from the fuel rail pressure sensor that is higher than the maximum normal operating range. A "Source High" condition almost always indicates an open circuit in the sensor wiring, a disconnected sensor, a short to a high-voltage source, or an internally failed rail pressure sensor.

• T4 series tractors
• T5 series tractors
• T6 series tractors
• T7 series tractors
• T8 series tractors
• T9 series tractors
• loader backhoes
• CR-series combines
• CR8.90
• CR9.90

1. 1

   Locate the fuel rail pressure sensor on the common fuel rail and inspect the 3-pin electrical connector for disconnected plugs, backed-out pins, moisture, or corrosion.

2. 2

   Trace the wiring harness from the pressure sensor back to the Engine ECU, looking for chafed wires, breaks, or areas where the harness might be shorting to a power source.

3. 3

   Using a multimeter, check the reference voltage at the sensor connector (typically 5V) and verify the ground circuit is intact (an open ground or broken signal return wire causes a default high voltage).

4. 4

   Ensure there are no severe fuel leaks, clogged fuel filters, or failing CP3 pumps that could cause erratic rail pressures.

1. 1

   Safety First

   Turn off the machine, remove the key, and disconnect the negative battery terminal. Warning: Wait several minutes after shutting off the engine before opening the fuel system, as common rail systems operate at extremely high pressures that can cause severe injury.

2. 2

   Disconnect the Sensor

   Unplug the electrical connector from the fuel rail pressure sensor.

3. 3

   Remove the Sensor

   Carefully unscrew the faulty pressure sensor from the fuel rail. Have a rag ready to catch any residual diesel fuel.

4. 4

   Clean the Port

   Ensure the threaded port on the fuel rail is clean and free of debris.

5. 5

   Install the New Sensor

   Thread the new OEM fuel rail pressure sensor into the rail. Tighten to the specific torque rating outlined in your engine's service manual (do not over-tighten, as this can damage the rail or sensor).

6. 6

   Reconnect

   Plug the electrical connector back into the sensor, ensuring it clicks and locks into place.

7. 7

   Restore Power and Clear Codes

   Reconnect the battery. Turn the ignition key to the ON position (without starting the engine) and use a diagnostic tool to clear the NH 3104 fault code.

8. 8

   Test Run

   Start the engine and check for fuel leaks around the new sensor. Verify that the engine runs smoothly without derating and that the fault code does not return.