Case IH 19544 – Engine Control Unit (ECU) / Aftertreatment System ECU: NOx offset min error detection

The exhaust aftertreatment system has detected that the voltage or calculated offset value from the downstream NOx sensor (Sensor 2, located after the SCR catalyst) has dropped below the minimum allowable threshold. This indicates that the sensor is either reading an implausible baseline value, has a wiring issue, or has internally failed.

• Tier 4b
• Magnum 180
• Magnum 200
• Magnum 220
• Magnum 240
• Farmall 110A
• Farmall 120A
• Farmall 130A
• Farmall 140A
• Axial-Flow 7240
• Axial-Flow 8240
• 750M

1. 1

   Inspect downstream NOx sensor connector terminals for debris, corrosion, or water intrusion (often caused by pressure washing).

2. 2

   Check the wiring harness leading to the downstream NOx sensor for chafing, melting from exhaust heat, or incorrect routing.

3. 3

   Inspect machine grounds and connector pins for damage or looseness, and verify the sensor is receiving the correct voltage (ensure a 12V sensor is not fitted to a 24V system).

4. 4

   Check for available ECU software updates via the CNH Electronic Service Tool (EST) to resolve overly sensitive NOx offset parameters.

1. 1

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

   The NOx sensor is mounted directly in the exhaust stream and gets extremely hot.

2. 2

   Locate the downstream NOx sensor (Sensor 2) and disconnect its electrical connector.

   The sensor is positioned in the exhaust pipe after the SCR catalyst/muffler. Disconnect it from the main engine harness.

3. 3

   Remove the NOx sensor from the exhaust bung.

   Use a specialized NOx sensor socket or a 22mm wrench. If seized, apply penetrating oil and allow it to soak to prevent stripping the exhaust bung threads.

4. 4

   Install the new NOx sensor.

   Apply a small amount of anti-seize compound only to the threads of the new sensor (do not get any on the sensor probe). Thread it into the exhaust bung by hand to prevent cross-threading, then torque to OEM specifications (typically around 50 Nm / 37 lb-ft).

5. 5

   Reconnect the electrical connector and route the harness.

   Ensure the wiring harness is secured with zip ties and routed away from direct heat sources or sharp edges.

6. 6

   Clear codes and verify the repair.

   Reconnect the battery. Use the CNH EST diagnostic tool to clear the 19544 fault code and reset the NOx sensor learned values if required by the ECU. Run the engine to operating temperature to verify the code does not return.