Nissan Repair: code p0420, nissan altima, catalyst system

Question
a light check engine turns on and I took my nissan altima 1998 to autozone, they check it and found a code p0420, what is this?

Answer
Israel,

The code P0420 is TW (Two-Way) Catalyst System, Bank 1.  Now, for me, I would be looking at upstream problems that would cause the catalyst to get out of wack.  I would tune up the engine and change the fuel filter, air filter and put a gas treatment in the tank with premium gas and then disconnect the battery for five minutes and clear the code and drive it.  Usually, there is a reason that it is running rich and a tune up is the common cause.  Email me back with what you find.