Nissan Repair: Catalytic Converter, nissan maxima 2005, mass airflow sensor

Question
Morning and Happy New Year. I am trying to get some info and hoping that maybe you can help me. I have a 6th Gen Nissan Maxima (2005) and my SES light came on. Now Autozone says the code was an O2 Sensor but under request by my parents (Both Nissan Owners) I took it to their dealership who told me that it was the Catalytic Converter that was bad and needed to be replaced. This is covered under the warranty. However he added that the Catalytic Converter caused my Mass Airflow Sensor to go bad and that is NOT covered under the warranty. What really got my goat was that he went on to tell me that my car was not safe to drive because the Converter was eating itself from the inside and if it went it could harm my engine. Now I am not a Car Mechanic but I am an aircraft mechanic. How does something that is downstream from the engine and is part of the exhaust system cause harm to my engine? Also how hard should I fight to get the MAF Sensor covered under the warranty since they are the ones telling me that the Converter caused the problem?
Thanks in advance.

Answer
Hi Edward -

You are correct. The dealership diagnosis sounds a little fishy to me. I can see if the CAT was plugged, which would create a lot of back pressure, eventually harming the engine, however I don't think this is the case here.

So, getting back to the beginning (please excuse me, as diagnosis is always a challenge when you cannot be physically there), Would you be able to get the exact code(s) that Autozone extracted from your car's CPU? And, how long ago was that? If it wasn't recent (I would say over a month), then it might be wise to do it again, sometimes there might be additional codes apparent (Like the MAF sensor, which would help with the trail of diagnosis.

Hope this helps, and please get back to me -
I am about to put in my vacation dates for this site, so if I am not available, you may email me at cjiwash@yahoo.com.

Happy New Year -
aloha
calvin