Case IH 3561 – Engine Control Unit (ECU): NOx value not plausible (After treatment plausibility)

The engine's onboard computer is receiving a signal from the Nitrogen Oxide (NOx) sensor that does not align with the expected emissions model. This most commonly indicates that the NOx sensor itself has failed and is providing unreliable data.

• Magnum (180–380)
• Steiger (350–620)
• Quadtrac (370–620)
• Maxxum (115–150)
• Puma (150–220)
• Farmall (110A–140A)
• Axial-Flow Combines 5130, 6130, 7130, 7230, 8230, and 9230
• Titan 2240, 3030, 3530, 4030, and 4530
• Wheel Loaders 521F through 1121F

1. 1

   Check for companion codes related to DEF quality, DEF level, or specific circuit codes (e.g., Open Load or Short Circuit) and address those first

2. 2

   Inspect the NOx sensor's wiring harness and the 5-pin MCON plug for chafing, pinched wires, or water ingress/corrosion

3. 3

   Check for exhaust leaks upstream of the NOx sensor, which can skew the readings

4. 4

   Inspect the sensor head for oil contamination (black) or excessive urea/DEF injection (white), which indicates an underlying engine or dosing issue

1. 1

   Prep the Machine

   Shut off the engine, apply the parking brake, chock the wheels, and allow the exhaust system to cool completely.

2. 2

   Locate the Sensor

   Locate the faulty NOx sensor on the exhaust aftertreatment system (either upstream or downstream of the SCR catalyst).

3. 3

   Disconnect Electronics

   Unclip the connecting cable from the vehicle's fixing points and disconnect the electrical plug.

4. 4

   Remove the Sensor

   Use a specialized NOx sensor socket to remove the sensor from the exhaust pipe. (Note: If the sensor is rusted or seized, a harmonic vibration tool/air hammer may be required to break it loose without damaging the exhaust bung threads).

5. 5

   Prep for Installation

   Inspect and clean the threading in the exhaust system. Do not use silicone sprays, oil sprays, or grease near the new sensor head, as this will contaminate and ruin it.

6. 6

   Install the New Sensor

   Thread the new sensor in and tighten to OEM torque specs. Route the new cable carefully, ensuring it is securely clipped into the factory fixing points to prevent chafing.

7. 7

   Clear Codes and Reset Derate

   Use a heavy-duty diagnostic tool (e.g., Jaltest, TEXA, or Cojali) to clear the fault codes. If the FPT engine has entered a derate mode (which occurs after 40 hours of active DEF system faults), you must use the diagnostic tool to reset the inducement/derate counter to restore full engine power.