About nox sensor

NOx sensors monitor the levels of nitrogen oxides emitted by diesel vehicles to ensure compliance with emission regulations. Most engines have two NOx sensors: an upstream sensor and a downstream sensor. Common fault causes include dust accumulation on the sensor soot, water intrusion, and/or cable damage, which will cause the check engine indicator light to light up.

What does a NOx sensor do?

The NOx sensor is a part of the SCR system used to measure the amount of nitrogen oxides in a vehicle’s exhaust. In this way, the SCR knows the appropriate amount of urea or ammonia to provide better fuel economy and fewer harmful emissions.

In addition to real-time measurement of NOx levels, some NOx sensors also pay attention to parameters such as O2 concentration and exhaust flow rate.

NOx Sensor Repair Tips

  • A degraded doser valve (DEF injector) may set NOx DTCs
  • Be sure to test the doser valve before replacing NOx sensors
  • After replacing a NOx sensor, be sure to check service information for any reset procedures
  • NOx sensors can’t tell the difference between NOx and ammonia
  • Performing a DPF regen will release ammonia from the SCR catalyst

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