Case IH 19356 – Engine Control Module (ECM) / Engine Management System (EMS): Downstream NOx sensor signal and NH3 sensor signal plausibility check failure

The Engine Management System (EMS) is receiving conflicting or illogical data when comparing the readings from the downstream Nitrogen Oxide (NOx) sensor and the Ammonia (NH3) sensor.

• Tier 4b
• 240 Series Axial-Flow Combines
• N-Series TLBs (580N)
• STM N Series Loaders
• Tier 4B Tractors (Farmall 110U, Maxxum 115)

1. 1

   Check Sensor Dew Point Status: Using a diagnostic tool, view the Dew Point parameter of the sensors. It must read Ready before accurate diagnostics can occur.

2. 2

   Check for Accompanying Codes: Look for related SCR/DEF codes (such as 19359, 19016, or 19017) that might pinpoint the exact sensor failing.

3. 3

   Wiring & Harness Inspection: Inspect the Selective Catalytic Reduction wire harness for the NH3 sensor and downstream NOx sensor for chafing, melting, or loose connections.

1. 1

   Initiate Warm-Up Cycle

   Turn the key switch ON, then OFF, then ON again. This restarts the dew point (warm-up) cycle. The sensors may return to a “Ready” status depending on engine shut-down time, engine coolant, and catalyst temperatures.

2. 2

   Inspect Sensors

   Locate the downstream NOx sensor (directly after the SCR/DOC assembly) and the NH3 sensor in the exhaust system. Remove them and inspect the tips for heavy soot packing, physical damage, or excessive moisture/DEF crystallization.

3. 3

   Replace Faulty Components

   If the wiring is intact and the sensors still fail the plausibility check after reaching operating temperature, replace the NH3 sensor and/or the downstream NOx sensor.

4. 4

   Clear Codes

   Cycle the controller power to clear the fault code, or use your diagnostic tool to clear the inactive code and run a forced SCR system test to verify the repair.