When vehicles with catalytic converters first appeared the oxygen sensors had a short life and were expensive to replace. But I have not had to replace on in a vehicle in the past 20 years so I assume they got better. I expect the same with the NOx sensors. I had one go out in my 2011 Duramax before it go to 10,000 miles.
It took trips to 3 different dealers to get it correctly diagnosed and repaired. My symptoms were erratic error messages as to mile left before needing to add DEF, i.e. going into limp mode, and greatly increased DEF consumption. The computer was not getting the right reading from the NOx sensor and so it would cause more and more DEF to be injected into the exhaust stream.
When the sensor was replaced the mechanic also re-routed the wiring. The factory had put the wiring so that a section lay on the EGR body which gets very hot, and another section was resting on the AC compressor.
