Case IH F-4378-09 - ECU – Engine Control Unit (ECU): CAN timeout error from NH3 sensor - NH3Fac message

The Engine Control Unit (ECU) has lost communication with the NH3 (Ammonia) sensor. The ECU expects to receive a specific CAN bus message frame ('NH3Fac') from the sensor at regular intervals to monitor the Selective Catalytic Reduction (SCR) emissions system. When this message is not received within the expected timeframe, a timeout error is logged.

• MAGNUM AFS Connect
• Steiger
• Magnum
• Puma
• Optum
• Maxxum
• Maxxum 115
• Farmall
• Farmall 110U
• Axial-Flow 6150
• Axial-Flow 7250
• Axial-Flow 8250
• Axial-Flow 240 series
• Farmlift 635
• Case CE 580N

1. 1

   Inspect the wiring harness and the 8-pin connector leading to the NH3 sensor on the exhaust system for physical damage, melted wires, or corrosion

2. 2

   Verify that the NH3 sensor is receiving proper operating voltage and has a solid ground, as an undervoltage condition will cause the sensor's internal CAN controller to drop offline

3. 3

   Test the CAN High and CAN Low lines between the NH3 sensor and the Engine ECU for continuity, and check for short circuits to ground or power

4. 4

   Verify that the CAN configuration in the Engine ECU is correct and that the ECU is properly communicating with other nodes on the network

1. 1

   Disconnect Power

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

2. 2

   Repair Wiring

   If the diagnostic checks reveal a broken wire, short circuit, or corroded connector in the exhaust harness, repair or replace the affected harness section.

3. 3

   Replace the NH3 Sensor

   If the wiring, power, ground, and CAN lines test good, the internal CAN controller of the NH3 sensor has failed. Disconnect the 8-pin connector from the NH3 sensor, unthread the NH3 sensor from the SCR exhaust pipe, apply high-temperature anti-seize to the threads of the new sensor (if not pre-applied) and install it into the exhaust pipe. Route the sensor wire away from extreme heat sources and reconnect the 8-pin harness.

4. 4

   Clear Codes

   Reconnect the battery, turn the key to the ON position, and use a diagnostic tool (like the Case IH Electronic Service Tool) to clear the F-4378-09 fault code.

5. 5

   Test Operation

   Start the engine and allow it to reach operating temperature to ensure the SCR system goes into closed-loop operation and the CAN timeout does not return.