October of 2010, I had to have the catalytic converter in my Nissan Titan replaced because my check engine light came on. It was covered under warranty even though I had a little over 80,000 miles and the Nissan dealer replaced it. Then two week later my check engine light came back on and I was told that it was probably just an O2 sensor, so I kept driving it until recently when I talked to someone else and they told me I needed to get it checked because I had more than one converter and it had probably gone bad. I took it to a repair shop and it came up an 420 code which they said is the front converter. I just would like to know what I can do to get Nissan to pay to have this converter fixed as well, and why they didn't just fix both of them at the same time and save me the problem? I would also like to know what causes the converter to go bad and what I need to do to keep it from messing up the new ones? I only have 90,000 miles on my truck and I have read that normally a converter doesn't go bad until after 150,000 miles.