Nissan Repair: Catalytic Converter, nissan sentra, muffler shop

Question
I am thinking of purchasing a 1999 Nissan Sentra and was told by the owner that it needs a catalytic converter. How do I know for sure it is bad and what causes failure?

Answer
you should notice a drop in power and also a higher running temperature.  also at night you may notice a slight glow from this thing if its heating up, it will also loose power ,on any kind of a hill or small incline. it may idle rough from time to time.  there are several warning signs of one going bad.  if your in doubt about it, you can have it checked.  they can drill a hole in it and check the back pressure.  this will tell you if its going bad.  this is actually the best way to check them, any muffler shop or a good repair shop can do this. good luck.