Things to know about replacing NOx sensors
28th Nov 2025
This video is all about the handling and installation of new NOx sensors from the mechanic's point of view. Correct installation of NOx sensors Troubleshooting and condensation Additional diagnostics in the event of discoloration Installation tips for the new NOx sensor Protection against water damage Configuration and adjustment Protective cover and sensitive handlingTechnical knowledge for workshops on the handling and installation of new NOx sensors
What are NOx sensors?
NOx sensors measure the concentration of nitrogen oxides in the exhaust gas and convert them into usable signals for engine management. These signals control exhaust gas aftertreatment and help to keep emissions as low as possible. They are essential for passenger cars, light commercial vehicles and heavy commercial vehicles with gasoline or diesel engines.
The installation of a NOx sensor is not a plug-and-play solution. They consist of a sensor module, connecting cable and control unit, which are calibrated at the factory. They must not be replaced individually. Do not use silicone sprays, oil sprays or grease in the area of the sensor, as this may impair its function.
Please note that the sensor material can absorb moisture from the air if it is stored for a long period of time. This fault usually disappears after the first heating. If you notice a lot of condensation in the exhaust, drive your vehicle extensively to remove condensation from the exhaust system before installing the sensor.
After removing the old sensor, you should check the sensor head for discoloration: Black due to oil or white due to excessive urea injection require additional diagnostics on the vehicle to prevent recurring damage.
Before installation, be sure to check the threading in the exhaust system. Make sure that the connecting cable is securely clipped into the vehicle-specific fixing points and that the cable is not chafed or pinched.
Corrosion can occur due to water entering the plug connections, particularly in the case of sensors on the underbody. Check these thoroughly before installation.
After installing the NOx sensor, it must be configured using a diagnostic device. Connect a battery charger for a stable power supply and start the adjustment. A test drive is then required to ensure functionality.
Do not forget to remove the protective cap from the sensor head before installation. The NOx sensor is a precise measuring instrument, so handle the entire unit with care - avoid heavy mechanical loads.
https://youtu.be/AvpQoorg4Kc