Case IH 19554 – Engine Control Unit (ECU) or Vehicle Control Module (VCM): NOx sensor plausibility check with other sensors

The engine management system detects that the signal coming from the Nitrogen Oxide (NOx) sensor is inconsistent, illogical, or out of range when compared to the data being reported by other engine and exhaust sensors.

• Tier 4b
• Maxxum (110–140)
• Puma (130–230)
• Magnum (180–310)
• 7240
• 8240
• Patriot 2250
• Titan 3540
• Farmlift Series (632, 635, 735, 742, 935)
• N-Series Loader Backhoes
• M-Series Crawler Dozers (850M, 1150M, 1650M, 2050M)

1. 1

   Check DEF/AdBlue Quality: Use a refractometer to verify that the DEF concentration is at the target value of approximately 32.5%.

2. 2

   Inspect Wiring and Connections: Inspect the sensor's wiring harness and the 5-pin MCON connector for animal bites, smoldering/heat damage, contact corrosion, or broken wires.

3. 3

   Check for Exhaust System Deposits: Inspect for massive soot or crystallized urea deposits in the exhaust that could block the sensor probe.

4. 4

   Verify On-Board Software: Check if the ECU has the latest software updates to adjust overly sensitive NOx sensor plausibility logic.

5. 5

   Rationality Check via Scan Tool: Use a diagnostic tester to read live data and compare the upstream (engine-out) and downstream (SCR-out) NOx readings.

1. 1

   Turn off the machine's ignition and disconnect the battery

   This prevents electrical shorts and ensures safety.

2. 2

   Locate the faulty NOx sensor

   Find the sensor on the exhaust aftertreatment system.

3. 3

   Disconnect the sensor's electrical connector

   Disconnect the 5-pin plug from the main wiring harness.

4. 4

   Carefully unscrew the NOx sensor module from the exhaust pipe

   Note: Penetrating oil may be required, as the threads often seize due to extreme exhaust heat.

5. 5

   Install the new OEM NOx sensor into the exhaust pipe

   Tighten it to the manufacturer's specified torque.

6. 6

   Route the wiring safely away from extreme heat sources

   Reconnect the electrical plug.

7. 7

   Reconnect the battery

8. 8

   Connect a diagnostic scan tool to the vehicle to clear the active and stored fault codes

   Error cleaning is required after fitting a new NOx sensor.

9. 9

   Run the machine and perform a test drive or a forced stationary regeneration

   This allows the ECU to verify the new sensor's plausibility and confirm the SCR system is functioning correctly.