Case IH 19537 – Engine Control Module (ECM) or Vehicle Control Module (VCM): NOx sensor plausibility check with other sensors

The engine's computer is receiving a signal from the Nitrogen Oxide (NOx) sensor (typically the downstream sensor) that does not logically align with the data provided by other sensors. This is triggered if the measured NOx level is mathematically implausible given the current engine load and DEF dosing rate.

• Tier 4b
• T4 series
• T5 series
• mid-range tractors
• 580N
• 580SN (Super N)
• 590SN
• B95
• B110

1. 1

   Inspect the exhaust piping upstream of the NOx sensor for leaks that could introduce unmetered oxygen.

2. 2

   Verify DEF dosing to ensure the DEF injector/dosing module is functioning correctly and not under-dosing.

3. 3

   Check the NOx sensor wiring harness and the connector at the ECM for chafing, melting, or corrosion.

4. 4

   Check for accompanying codes related to the lambda sensor, EGR system, or DEF quality and address these first.

5. 5

   Remove the NOx sensor and visually inspect the probe for heavy soot packing or white DEF crystallization.

1. 1

   Read and Record

   Connect the CNH Electronic Service Tool (EST) to read all active and stored codes.

2. 2

   Clear and Retest

   If no wiring or exhaust leaks are found, clear the fault code. Perform a forced DPF regeneration or an SCR system test to see if the code returns.

3. 3

   Remove the Sensor

   If the code is hard-set or returns immediately, the NOx sensor itself has likely failed internally. Disconnect the sensor's electrical connector and use a specialized NOx/O2 sensor socket to remove the sensor from the exhaust pipe.

4. 4

   Clean the Port

   Clean the threads in the exhaust bung using a thread chaser to ensure the new sensor seats correctly.

5. 5

   Install the New Sensor

   Install the replacement OEM NOx sensor. Apply a high-temperature anti-seize compound to the threads only (most OEM sensors come with this pre-applied). Torque to the manufacturer's specification.

6. 6

   Route Wiring

   Secure the sensor's control module and route the wiring harness exactly as it was from the factory, ensuring it is kept away from extreme heat sources.

7. 7

   Reset and Relearn

   Use the CNH EST to clear the codes and reset the NOx sensor learned values/adaptations in the ECM. Run the machine under load to ensure the readiness monitors pass.