How often should you replace your Nox Sensors

The first set of nox sensors(factory)lasted for 4 years, then they went in a really bad spot in Montana a long way from a volvo dealership. It is coming up to 4 years since the replacement and the start of winter. So thinking of replacing them in November at the next oil change/pm. Was the first set just unlucky or is 4 years about the lifetime for them? Opinions or experience appreciated. Thanks in advance.

 

Thanks Nasriza for your info. That is what happened in Montana near Helena, Dealership in Great Falls was closed with Calgary being the closest one that was open. Cost me 3 days by the time all was done. I know you said 3 years but I will have them replaced at the next oil change. Costs money but so did sitting in Calgary. I prefer to replace items before the code comes up if possible.

 

I disconnected the speed sensor just to get me to Calgary. As you said expensive to replace the sensors but worth it to do before you get a code and a derate.Thanks again for the help