4.2.268. SPN 521005, FMI 2, Upstream NOx sensor value implausibleΒΆ

Description

EEM4 monitoring system has detected implausible NOx sensor value. Sensor value was evaluated during driving cycle and plausibility test result was failure.

Possible causes are:

  • The upstream NOx sensor is defective
  • The upstream NOx sensor is installed incorrectly
  • Possible tampering

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 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 upstream NOx sensor assembly. Make sure the sensor is assembled according to ASP installation instructions.(see Engine sensors overview)
  • Check the operation with another upstream NOx sensor to see if the sensor is defective. (see NOx sensor)
  • Possible tuning chip may interfere NOx sensor signal.