Case IH 3612 – Engine Control Unit (ECU): Catalyst efficiency lower than second Nox prediction threshold level

The Engine Control Unit (ECU) monitors the efficiency of the Selective Catalytic Reduction (SCR) system by comparing the readings from the upstream and downstream NOx sensors. Code 3612 is triggered when the ECU detects that the SCR catalyst is failing to reduce NOx emissions below the acceptable secondary threshold.

• Magnum
• Steiger
• Puma
• Maxxum
• Optum
• Farmall
• Axial-Flow
• 621F
• 721F
• 821F
• 921F

1. 1

   Check the Diesel Exhaust Fluid (AdBlue) quality using a refractometer for contamination, dilution, or expiration.

2. 2

   Check the upstream and downstream NOx sensors for plausibility, as a faulty sensor can falsely report high NOx levels.

3. 3

   Inspect the DEF injector for crystallization, blockages, or leaks that would prevent the correct amount of fluid from entering the exhaust stream.

4. 4

   Inspect the exhaust piping between the engine turbocharger and the SCR catalyst for leaks that can alter exhaust flow and temperature.

5. 5

   Check if the ECU and the Denoxtronic (DNox) supply module require a software update.

1. 1

   Verify the Code

   Connect a diagnostic tool (such as the Case IH Electronic Service Tool or Jaltest) to verify Code 3612 and review freeze-frame data.

2. 2

   Test and Replace DEF

   If the DEF concentration is not exactly 32.5% urea, drain the DEF tank completely, flush it, and refill it with fresh, high-quality DEF.

3. 3

   Perform a Doser Quantity Test

   Use the diagnostic tool to run a DEF dosing test. If the injector fails to spray the commanded amount, remove the doser, clean any crystallized urea with warm water, or replace the DEF injector module.

4. 4

   Monitor NOx Sensors

   View live data for the NOx sensors while the engine is running. If a sensor reading is erratic, drops out, or fails to respond to throttle changes, replace the faulty NOx sensor.

5. 5

   Perform a Healing Cycle / Forced Regen

   If the fluid, doser, and sensors are functioning correctly, run the machine under a heavy load to achieve exhaust temperatures over 425°F for at least 30 minutes to allow the catalyst to heal or regenerate.

6. 6

   Replace the SCR Catalyst

   If the code persists after all other components are verified and a high-temp cycle is completed, the SCR catalyst muffler assembly is permanently degraded and must be replaced.

7. 7

   Update Software & Clear Codes

   Flash the ECM and DNox unit to the latest software versions. Clear the fault codes and test drive the machine under load to verify the repair.