Case IH F-3226-10 - ECU – Engine Control Unit (ECU / ECM): Downstream NOx sensor signal is stuck at a constant value or Abnormal Rate of Change

The sensor located after the Selective Catalytic Reduction (SCR) catalyst is failing to register expected fluctuations in nitrogen oxide levels. The underlying condition is typically caused by an intermittent wiring issue, sensor contamination, or an internal circuit failure within the sensor itself.

• MAGNUM AFS Connect
• Case IH 240 Series Axial-Flow Combines
• Case IH Magnum 235 - 340 (Series 4) Tractors
• Various other Case IH and New Holland tractors utilizing the same emissions architecture

1. 1

   Verify if F-3226-10 is the only active fault code. If there are other codes related to the DEF dosing system or exhaust temperatures, diagnose those first.

2. 2

   Inspect the exhaust system pipeline for broken pipes, leaks, or loose connections near the NOx sensor.

3. 3

   Inspect the downstream NOx sensor wiring harness, connector, and terminals. Look for melted wires, corrosion, or physical damage that could cause a false contact or short to ground.

4. 4

   Check if the sensor has been subjected to prolonged exposure to contaminants, which can cause internal failure.

1. 1

   Cool down exhaust system

   Ensure the machine is turned off and the exhaust system has completely cooled down to prevent burns.

2. 2

   Repair wiring or connector

   If the diagnostic inspection reveals damaged wiring, connectors, or terminals, repair the harness or replace the connector.

3. 3

   Disconnect sensor

   If the wiring and connectors are clean and undamaged, the sensor itself has likely failed or reached its end-of-life and must be replaced. Disconnect the electrical connector for the downstream (outlet) NOx sensor.

4. 4

   Remove faulty sensor

   Unthread the faulty NOx sensor from the exhaust pipe (located behind the catalytic converter).

5. 5

   Install new sensor

   Install the new NOx sensor and tighten it to the manufacturer's specified torque.

6. 6

   Reconnect harness

   Reconnect the electrical harness.

7. 7

   Reset and regenerate

   Perform a system reset using an electronic service tool. It is highly recommended to perform a parked regeneration to verify the repair and ensure the SCR system is functioning correctly and the code clears.