Case IH 19188 (F-3224-18) - ECU – Engine Control Unit (ECU): Upstream NOx sensor self-diagnosis result is out of the acceptable limit

The upstream NOx sensor (located before the SCR catalyst) is either not measuring correct values, the engine is emitting an unexpected quantity of NOx, or the ECU's NOx estimation model is incorrect.

• VESTRUM CVX
• 240 Series (7240, 8240, 9240) Axial-Flow Combines
• 140 Series (5140, 6140, 7140) Axial-Flow Combines
• Magnum (180 to 380)
• Puma (150 to 220)
• Steiger / Quadtrac (370 to 620)
• Maxxum (115 to 150)
• Farmall A series
• Patriot (2250, 3240, 3340, 4440)
• Titan (3040, 3540, 4040, 4540)

1. 1

   Verify the presence and correct connection of the Upstream NOx Sensor to the CAN network. Ensure the CAN controller is functioning correctly.

2. 2

   Inspect the wiring harness leading to the NOx sensor for short circuits, open circuits, or high resistance (chafed wires are common near the exhaust).

3. 3

   Check for battery or alternator defects. High or low voltage during cold starts can trigger false sensor defects.

4. 4

   Remove the sensor and inspect the tip for physical damage, heavy soot buildup, or DEF crystallization.

5. 5

   Verify that the engine itself is not over-producing NOx due to a separate mechanical issue (e.g., EGR failure or injector issues).

1. 1

   Preparation

   Turn off the machine, allow the exhaust system to cool completely, and disconnect the battery.

2. 2

   Locate the Sensor

   Locate the Upstream NOx sensor on the exhaust pipe (positioned between the turbocharger and the DOC/SCR catalyst assembly).

3. 3

   Disconnect

   Unplug the NOx sensor's electrical connector from the main engine wiring harness.

4. 4

   Removal

   Use a specialized NOx sensor socket or wrench to remove the retaining nut and carefully extract the sensor from the exhaust bung.

5. 5

   Clean the Port

   Inspect the exhaust bung threads for damage or carbon buildup. Clean the threads with a thread chaser if necessary.

6. 6

   Preparation of New Sensor

   Apply a light coating of high-temperature anti-seize compound (e.g., Cummins Part Number 3824879) to the threads of the new NOx sensor. Caution: Do not get anti-seize on the sensor tip, as this will ruin the sensor.

7. 7

   Installation

   Thread the new NOx sensor into the exhaust system by hand to prevent cross-threading, then tighten the retaining nut to the OEM torque specification (typically 50 N·m or 37 ft-lb).

8. 8

   Reconnect

   Plug the NOx sensor electrical connector back into the OEM wiring harness.

9. 9

   Clear Codes

   Reconnect the battery, turn the key to the ON position, and use a diagnostic scan tool (like the CNH Electronic Service Tool) to clear the fault codes.

10. 10

    Validation

    Start the engine and let it reach operating temperature to verify the fault code does not return.