That is very interesting. When adding an exhaust there are a few things that can be changed that can make things different or leave things in working order. For example, you may have heard of cat back exhaust where the exhaust is only aftermarket beyond the catalytic converter. This generally leaves all the oxygen sensors and other forward cats unchanged and seldom causes problems. The big issue is not negating stock sensors. This gets to be more and more of an issue as cars have more and more sensors and they become very sensitive to changes. Dealers do not like when cars get modified under warranty as it generally voids it and makes diagnostics very hard. Diagnostics is generally the most labor consuming part of servicing a car.
I am intrigued by the "part that does not exist" remark. I am assuming you are talking about a Nissan dealer telling you this. If it is not, I would get an opinion from a Nissan dealer, but not until you call the aftermarket exhaust manufacturer and get them to explain what is going on. Also, go to an Advance Auto or Auto Zone and get them to read the codes and see what comes back. It is not quite as exact as other code readers but it might give you something to go on when you call the exhaust manufacturer.
Let me know how it goes and remember, try to get all the info you can before going after Nissan. Also, some dealerships are kinder than others.
I will keep an eye out for your reply.
Saturday, May 9th, 2015 AT 8:02 PM