3.2.376. SPN 521007, FMI 10, SCR system ERROR: DEF backflow line blocked or implausibleΒΆ

Description

The EEM4 monitoring system has detected an SCR system ERROR. The DEF supply module backflow line is defective.

Possible causes are:

  • The DEF backflow line is defective. (A possible blockage or a mechanical defect).
  • The DEF supply module backflow line connector is defective.
  • The DEF supply module main filter is defective.
  • The used reducing agent (DEF/AdBlue) has been contaminated.
  • The DEF supply module 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 bakflow line visually to detect any mechanical failures eg. the hose is flattened.
  • Change the DEF supply module main filter and the backflow connector.
  • Check the used reducing agent (DEF/AdBlue) for contamination and change it, if necessary.
  • Check the operation with another DEF supply module to see if the supply module is defective.