Case IH 19180 (F-3234-18) - ECU – Engine ECU: Downstream NOx sensor self-diagnosis result is lower than the limit.

The engine's Selective Catalytic Reduction (SCR) aftertreatment system has run an internal self-check on the downstream Nitrogen Oxide (NOx) sensor, and the sensor's diagnostic values or readings have fallen below the minimum acceptable threshold. This typically points to a failing sensor, a wiring issue, or an exhaust anomaly affecting the sensor's ability to read correctly.

• VESTRUM CVX
• Case IH 240 Series Axial-Flow Combines (7240, 8240, 9240)
• Case IH Magnum Tractors (250-380 series)
• Case IH Austoft 9900 Sugarcane Harvesters

1. 1

   Inspect the downstream NOx sensor (located in the exhaust pipe after the SCR catalyst/DOC) for physical damage or heavy soot accumulation.

2. 2

   Check the sensor's wiring harness and electrical connector for chafing, melting, corrosion, or loose pins.

3. 3

   Inspect for exhaust leaks between the engine and the downstream NOx sensor, which can introduce fresh air or allow exhaust to escape.

4. 4

   Ensure the DEF/AdBlue fluid is not contaminated and the tank is adequately filled, as poor quality can affect NOx conversion.

5. 5

   Look for other active codes related to the upstream NOx sensor (e.g., 19187/19188), DOC temperatures, or DEF dosing to rule out a broader aftertreatment failure.

1. 1

   Preparation

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

2. 2

   Removal

   Locate the downstream NOx sensor on the exhaust tailpipe. Disconnect the electrical harness connector.

3. 3

   Extraction

   Carefully unscrew the NOx sensor from the exhaust bung. (Note: Use penetrating oil if the threads are seized to avoid damaging the exhaust pipe threads).

4. 4

   Installation

   Install the new downstream NOx sensor. Ensure the threads are treated with high-temperature anti-seize (if not pre-applied by the manufacturer) and tighten to the OEM specified torque.

5. 5

   Reconnection

   Reconnect the electrical harness securely.

6. 6

   Clear Codes

   Reconnect the battery and turn the ignition on. Use a certified diagnostic scan tool to clear the active and inactive fault codes.

7. 7

   System Reset/Validation

   Perform an SCR system reset. If the fault caused an engine power loss/derate, the DEF/AdBlue tank level must be raised above 12% total volume, and a specific validation restart sequence must be followed to restore full engine power.