Case IH F-4225-16 - ECU – Engine Control Unit (ECU) / Engine Control Module (ECM): SCR catalyst efficiency lower than first NOx production threshold level

The Selective Catalytic Reduction (SCR) system is not reducing Nitrogen Oxide (NOx) emissions effectively. The downstream NOx sensor is detecting NOx levels that exceed the allowable emissions threshold, indicating that the catalyst is either degraded, not receiving enough Diesel Exhaust Fluid (DEF/AdBlue), or a sensor is providing inaccurate readings.

• MAGNUM AFS Connect
• Axial-Flow Combines 240 Series (7240, 8240, 9240)
• Axial-Flow Combines 140 Series
• Axial-Flow Combines 150 Series
• Puma
• Magnum
• Maxxum
• Optum

1. 1

   Check for other active fault codes involving fueling, air quantity determination, or NOx sensors (e.g., SPN 3234-2, 3224-2, or 4425-31)

2. 2

   Verify DEF/AdBlue quality and concentration using a DEF refractometer

3. 3

   Use a diagnostic tester to monitor estimated NOx versus actual readings from upstream and downstream NOx sensors for implausible values

4. 4

   Verify the DEF dosing valve is not mechanically blocked or suffering from overheat protection limits

5. 5

   Check engine parameters including humidity sensor, fuel pressure sensor, and engine injection timing for poor combustion

1. 1

   Resolve Active Codes

   If any codes related to the NOx sensors, DEF pump, or engine fueling are present, diagnose and repair those circuits first. Clear the codes and run the machine to see if 4225-16 returns.

2. 2

   Test and Clean the Dosing Valve

   Perform a DEF dosing quantity test via the diagnostic software. If the spray pattern is poor or volume is low, remove the DEF dosing valve, clean any crystallized urea with warm water, and retest. Replace the valve if it fails the quantity test.

3. 3

   Replace DEF Fluid

   If the DEF is contaminated with diesel, water, or has degraded, drain the tank completely, flush it, and refill with fresh, high-quality DEF.

4. 4

   Replace NOx Sensor(s)

   If the diagnostic tester shows the downstream NOx sensor is reading erratically or mirroring the upstream sensor perfectly despite proper DEF dosing, replace the faulty NOx sensor.

5. 5

   Replace the SCR Catalyst

   If DEF quality is perfect, the dosing valve is injecting the correct amount of fluid, engine combustion is normal, and the NOx sensors are functioning properly, the SCR catalyst substrate has failed or degraded. The SCR catalyst/muffler assembly must be replaced.