Case IH 19423 – Engine Control Module (ECM): Upstream NOx sensor comparison to a calculated NOx value failure

The Engine Control Module (ECM) continuously calculates an expected (modeled) engine-out Nitrogen Oxide (NOx) value based on current engine operating parameters (RPM, load, temperature, etc.). It then compares this calculated value to the actual physical reading provided by the Upstream NOx sensor (located before the SCR catalyst). If the physical sensor's reading deviates from the ECM's calculated model beyond an acceptable threshold, fault code 19423 is triggered. This typically indicates a drifted/failed upstream NOx sensor, an exhaust leak, or an engine combustion issue (like an EGR fault) causing actual NOx levels to skew outside the expected model.

• Tier 4b
• Magnum 180
• Magnum 200
• Magnum 220
• Magnum 240
• Magnum 250
• Magnum 280
• Magnum 310
• Magnum 340
• Puma 150
• Puma 150 CVT
• Puma 165
• Puma 165 CVT
• Steiger
• 5140
• 6140
• 7140
• 7240
• 8240
• 9240
• Patriot 2250
• Patriot 3240
• Patriot 3340
• Patriot 4440
• Titan 3040
• Titan 3540
• Titan 4040
• Titan 4540
• N-Series Tractor Loader Backhoes

1. 1

   Check for accompanying codes related to the EGR system, intake pressure, or fuel delivery, as mechanical faults can cause actual NOx levels to skew.

2. 2

   Inspect the exhaust system for leaks between the engine manifold and the upstream NOx sensor, which can introduce oxygen and cause false readings.

3. 3

   Inspect the C186 connector (5-pin female) and the wiring harness leading to the upstream NOx sensor for chafing, corrosion, or loose terminal pins.

4. 4

   Remove the upstream NOx sensor and inspect the probe tip for heavy soot packing, physical damage, or moisture contamination.

5. 5

   Check OEM service bulletins to see if an ECM flash update is available to widen the acceptable parameters of the calculated NOx model.

1. 1

   Turn off the machine, remove the key, and disconnect the battery

   This prevents electrical spikes. Note: The exhaust system must be cool before attempting this repair.

2. 2

   Locate the Upstream NOx sensor

   Situated on the exhaust pipe, between the engine turbocharger outlet and the DOC/SCR catalyst assembly.

3. 3

   Disconnect the sensor's electrical connector

   Disconnect it from the main engine harness.

4. 4

   Unscrew the sensor from the exhaust pipe

   Use a specialized NOx sensor socket or a 22mm wrench.

5. 5

   Clean the exhaust pipe bung threads

   Ensure the threads are clean before installing the new sensor.

6. 6

   Apply high-temperature anti-seize compound to the threads of the new NOx sensor

   Caution: Do not get any anti-seize on the sensor tip, as this will permanently ruin the element.

7. 7

   Install the new sensor into the exhaust pipe

   Thread the new sensor into the exhaust pipe by hand to prevent cross-threading, then torque to 50 N·m (37 ft-lb).

8. 8

   Reconnect the electrical connector

   Secure the wiring away from extreme heat sources.

9. 9

   Clear the fault code and test the machine

   Reconnect the battery, turn the ignition on, and use a diagnostic service tool to clear the inactive 19423 fault code. Run the engine to operating temperature to ensure the code does not return.