Steuergerät des NOx-Sensors defekt

The small electronics package that comes as part of a NOx sensor, failed. These are not simple sensors: the element needs around 800°C and a two-stage measurement, so each sensor carries its own module which runs the heater, performs the measurement, and reports the result over the vehicle's data network rather than as a voltage.

That architecture is why a communication fault presents as a sensor fault. If the module cannot talk, the engine module reports the sensor as faulty — while the sensing element is perfect. So a network or bus code stored alongside is worth reading before a part is ordered.

It is almost never sold separately. The module is moulded into the harness a fixed distance from the sensor, so a module fault means buying the whole assembly — which is why eliminating the connector, the supply and the earth first genuinely matters here.

Its position is what kills it. It hangs under the vehicle in road spray and salt, close enough to the exhaust to be heat-cycled continuously. Water ingress and heat-fatigued solder joints are the ordinary findings.

Where two of these sensors are fitted, they are usually not interchangeable — different lengths, different network addresses — so confirm the part before fitting, and expect some vehicles to require coding afterwards.