Massey Ferguson 4090.18 – Engine Control Unit (ECU) / AGCO SISU POWER EEM4: NOx Are High In The Exhaust / SCR system malfunction: Measured NOx emission implausible.

The engine management system has detected that the measured Nitrogen Oxide (NOx) emissions in the exhaust are implausibly high. This triggers a warning lamp, logs an active CAN fault, and will eventually result in a heavy engine power reduction (Degradation Level 2 or 3) after a set time defined by emissions regulations.

• 7616
• 5612
• 7622
• Interim Tier 4 (2012-2015)
• 7614
• 5611
• 7615
• 5610
• 5613
• 7620
• 5609
• 7618
• 5608
• 7619
• 7626
• 7624
• 4607M
• 4609M
• 4708
• 4709
• 4710
• 5608-5613
• 5708-5713
• 6612-6616
• 6712-6718
• 7614-7626
• 7714-7726
• 8727-8740
• Activa 7340
• Activa 7344
• Activa 7345
• Activa 7347
• BETA 7360
• 9540
• 9560

1. 1

   Clear the Code: Save the error log, erase it, and restart the ECU. If the fault returns during the next driving cycle, proceed with physical checks.

2. 2

   Check DEF/AdBlue Quality: Test the urea concentration, as contaminated, diluted, or expired Diesel Exhaust Fluid is the most common cause.

3. 3

   Check DEF Dosing Operation: Verify that the SCR system is actually able to dose DEF into the exhaust stream.

4. 4

   Test the Dosing Module: Swap or test operation with a known-good DEF dosing module to see if the current doser is defective or blocked.

5. 5

   Inspect the SCR Catalyst: Remove the DEF dosing valve and visually inspect the inside of the SCR catalyst for crystallized DEF/AdBlue deposits or physical blockages.

6. 6

   Check for Tuning Chips: Ensure no aftermarket engine tuning chips are installed, as these can artificially raise NOx output beyond the SCR system's capacity.

1. 1

   Address Fluid Quality

   If the DEF is suspected to be bad, completely drain the DEF tank, flush the system, and refill with fresh, valid AdBlue/DEF.

2. 2

   Clean the Catalyst

   If crystallized DEF deposits are found inside the SCR catalyst during inspection, clean the dosing port and catalyst face according to OEM guidelines.

3. 3

   Replace the DEF Doser

   If the dosing module fails the operational test (unable to spray/dose), replace the DEF doser valve.

4. 4

   Replace the NOx Sensor

   If the DEF fluid is good, the doser is spraying correctly, and the catalyst is clear, the NOx sensor itself is likely providing implausible readings and must be replaced.

5. 5

   Reset the System

   After repairs, clear the fault codes and run a forced regeneration or SCR system test via the service tool to validate the repair and remove the engine derate.