Case IH 19179 – Engine Management System (EMS) / Engine ECU: Downstream NOx sensor self-diagnosis result is higher than the limit.

The downstream NOx sensor fails its internal self-diagnosis check (often during an afterrun cycle) and returns a value that is higher than the acceptable programmed limit. This indicates a potential failure of the sensor itself or a severe catalyst inefficiency.

• Tier 4b
• 240 Series Axial-Flow Combines (7240, 8240, 9240)
• Puma series (150, 165, 185, 200, 220)
• Farmall series (110A, 120A, 130A, 140A)
• Optum CVT series (270, 300)
• N-Series Loaders
• Farmlift Telehandlers

1. 1

   Check DEF/AdBlue quality — questionable concentration can cause SCR faults. If suspect, drain, clean, and refill the tank with approved fluid.

2. 2

   Verify sensor 'Dew Point' status using a diagnostic tool. Ensure the sensor is capable of reaching the 'Ready' state after a proper engine warm-up cycle.

3. 3

   Inspect the downstream NOx sensor wiring harness and connector for melting, corrosion, or short circuits to ground.

4. 4

   Check for exhaust leaks in the piping between the engine and the SCR catalyst, which can skew oxygen and NOx readings.

1. 1

   Preparation

   Turn off the engine and allow the exhaust system to cool completely to avoid severe burns.

2. 2

   Locate the Sensor

   Locate the downstream NOx sensor, which is threaded into the exhaust pipe directly after the SCR catalyst.

3. 3

   Disconnect

   Unplug the electrical connector linking the NOx sensor to the engine wiring harness.

4. 4

   Removal

   Using a specialized NOx sensor socket or a properly sized wrench, carefully unthread the faulty sensor from the exhaust pipe.

5. 5

   Installation

   Apply a small amount of high-temperature anti-seize compound to the threads of the new sensor (if it does not come pre-applied). Caution: Do not get any anti-seize on the sensor probe tip, as this will ruin the sensor.

6. 6

   Torque

   Thread the new sensor into the exhaust pipe and tighten it to the OEM torque specification.

7. 7

   Reconnect

   Plug the electrical connector back into the harness and ensure it clicks securely into place.

8. 8

   Clear and Relearn

   Turn the key switch ON. Use a diagnostic tool to clear the 19179 fault code. Start the machine and run the engine through a warm-up cycle so the new sensor can reach its 'Ready' status and verify the repair.