Case IH 3611 – Engine Control Unit (ECU): Catalyst efficiency lower than first Nox prediction threshold level

The Selective Catalytic Reduction (SCR) system is operating below the expected efficiency threshold for reducing Nitrogen Oxide (NOx) emissions. It acts as an early warning (Level 1) and typically occurs prior to fault code 3612.

• Steiger
• Magnum
• Puma
• Maxxum
• Farmall
• Optum
• Axial-Flow
• Patriot
• Titan

1. 1

   Verify DEF Quality: Ensure the Diesel Exhaust Fluid (DEF/Urea) is not degraded, contaminated, or diluted.

2. 2

   Check NOx Sensors for In-Range Failures: Place the downstream NOx sensor in the dosing module hole and use the Electronic Service Tool (EST) to verify the reading against estimated NOx output, or swap with a known good sensor.

3. 3

   Inspect the SCR Catalyst Substrate: Remove the exhaust pipe and visually inspect the catalyst substrate inside the muffler for physical damage, face plugging, or cracking.

1. 1

   Replace downstream NOx sensor

   If the diagnostic tests prove the NOx sensor is reading out of range, replace the downstream NOx sensor.

2. 2

   Replace DEF filter

   If DEF contamination is suspected, drain the DEF tank, flush the system, and replace the DEF filter assembly.

3. 3

   Replace the SCR Catalyst

   If visual inspection reveals a cracked, melted, or damaged honeycomb substrate, the SCR catalyst/muffler assembly must be replaced. Disconnect the exhaust piping and sensor harnesses, unbolt and remove the damaged SCR catalyst cluster, install the new SCR catalyst and torque all exhaust clamps to OEM spec to prevent exhaust leaks.

4. 4

   Clear Codes

   Use the CNH Electronic Service Tool (EST) to clear the fault codes. Note: Emissions-related codes may require a forced regeneration or a specific drive cycle to fully clear from the ECU's active memory.