3.2.199. SPN 4090, FMI 31, NOx limits exceededΒΆ

Description

The NOx limits are exceeded. The root cause is unknown.

Possible causes are:

  • The SCR system is unable to dose.
  • The DEF dosing module is defective or blocked.
  • The used reducing agent (DEF/AdBlue) is contaminated.
  • The SCR catalyst is defective.

Reaction in EEM

The FC is stored and the warning lamp is activated. The CAN message indicates active fault.

NOTE: The present fault is classified as an emission related fault. Engine power will be reduced after a certain time which is defined by an authority.

Solution

First save the error log and then erase it. Restart the ECU after erasing the error log. If the fault occurs again during the next driving cycle, check the following paths:

  • Check the used reducing agent (DEF/AdBlue) quality. If there are any suspicions that a poor quality reducing agent has been used, the tank needs to be emptied, flushed and refilled with valid reducing agent.
  • Check the DEF system operation. Make sure the SCR system is able to dose the DEF/AdBlue.
  • Check that the both NOx sensors are effective. Change the defective sensor to a new one.
  • Check the operation with another DEF dosing module to see if the dosing module is defective.
  • Check the SCR catalyst condition. Remove the dosing valve and look inside the catalyst and the nozzle. Check for a possible DEF/AdBlue deposit problem or a blockage.