3.2.390. SPN 521024, FMI 31, Relative O2 concentration error between upstream and downstream NOx sensorsΒΆ

Description

There is a relative O2 concentration error between the upstream and the downstream NOx sensors.

Possible causes are: * The upstream NOx sensor is defective. * The downstream NOx sensor 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 that the upstream and the downstream NOx sensors are connected correctly.
  • Check the NOx sensor wiring, the connectors and the contact surfaces of the connector pins (possible oxidation).
  • Check that the both NOx sensors are effective. Change the defective sensor to a new one.

See NOx sensor for reference.