Case IH 19539 – Engine Control Module (ECM) or Vehicle Control Module (VCM) / Denoxitronic Control Unit (DCU15): Offset Min/Max error detection for NOx extended Offset value

The engine's control module has detected an implausible baseline reading (offset) from the NOx sensor, which has drifted outside programmed minimum or maximum allowable limits. This is typically caused by a degraded sensor element, heavy soot/DEF contamination, or a failing internal sensor heater.

• Tier 4b
• Magnum (180-380)
• Puma (140-240)
• Maxxum (115-150)
• Optum (250-300)
• Farmall
• Steiger series
• N-Series Loader Backhoes (e.g., 580N)
• F-Series Wheel Loaders
• Patriot Sprayers
• Titan Floaters
• Axial-Flow Combines (5130-9230)

1. 1

   Check the ECU for other active codes, specifically for NOx sensor power supply (e.g., 19536), CAN communication timeouts, or DEF dosing module errors. Diagnose these first if present.

2. 2

   Monitor live data using the CNH Electronic Service Tool (EST). A static/warm-up NOx sensor should read approximately 500 ppm, dropping to 250-270 ppm once the exhaust heats up and DEF is injected. Erratic or stuck readings indicate a failed sensor.

3. 3

   Remove the sensor and visually inspect the probe. Heavy soot indicates rich combustion, white crystalline buildup indicates a DEF doser leak, and heat discoloration indicates lean combustion.

4. 4

   Check DEF quality using a refractometer to ensure the AdBlue/DEF concentration is at the target value of 32.5%. Poor DEF quality can skew NOx readings.

5. 5

   Inspect the sensor's wiring harness and connector for water intrusion, melted wires, or pin corrosion.

1. 1

   Disconnect battery

   Turn off the machine's ignition and disconnect the negative battery cable.

2. 2

   Locate faulty NOx sensor

   Locate the faulty NOx sensor. Verify via your diagnostic tool whether the upstream (pre-SCR) or downstream (post-SCR) sensor is logging the offset error.

3. 3

   Disconnect electrical connector

   Disconnect the electrical connector for the NOx sensor module and unclip the wiring harness from the frame.

4. 4

   Unscrew sensor probe

   Using a 22mm wrench or a specialized NOx sensor socket, carefully unscrew the sensor probe from the exhaust pipe.

5. 5

   Inspect and clean mounting threads

   Inspect the M22 x 1.5 mounting threads on the exhaust pipe. Clean the threads with a thread chaser if necessary to ensure a proper seal, as an exhaust leak at the bung will cause incorrect readings.

6. 6

   Install new NOx sensor

   Install the new NOx sensor. Do not allow any anti-seize to touch the sensor tip. Torque to the manufacturer's specification.

7. 7

   Route wiring and reconnect plug

   Route the wiring harness safely away from extreme heat sources and reconnect the electrical plug.

8. 8

   Reconnect battery

   Reconnect the battery.

9. 9

   Clear codes and perform resets

   Connect the CNH EST diagnostic tool, clear the fault codes, and perform any required SCR system resets or NOx sensor adaptations so the ECU recognizes the new sensor's baseline.