@ All, with my 350 BT the motor lamp lights up. Lt. friendly it would be a defect of the NOX sensor in front of the cat. He said this must be exchanged and then all two are exchanged (one sensor in front of the cat and one sensor behind the cat) Unit price over 530 € plus installation. The expensive on the sensors is the ECU that is with a cable on the sensor with it. Now I have researched something and found out that in 99% of the defects the ECU is not defective. Now my question has someone here already changed the Nox sensors without ECUs ? The sensors are almost all the same and are from Bosch or NKG. The ECU can then be soldered accordingly. I am now looking for the right sensors. Does anyone have a link ? VG Walter