Symptoms Of Bad Catalytic Converter?

[todd]

I have a 2003 Xterra with 3.3 and 219,000 Miles. I am receiving codes P0420 and P0430 along with a P1456 code for fuel temperature sensor. The SES light has been on for knock sensor for a couple years now so I dont know when these codes appeared. The engine started hesitating, stumbling at cruising speed then it suddenly got better for a couple days and then started getting worse and starting shutting off at stop lights.

Could these symptoms be from a loose or leaking gas cap as the AZ print out suggests? (going to Nissan dealer now to get a gas cap to eliminate that)
Are these the symptoms of a bad catalytic converter?
Could the problem be just bad oxygen sensors?

Thanks for any info or recommendations.

 

[TerryD]

Depending on how long you've had the converter codes, they may be damaged but i would work toward them rather than replacing them first.

I'm not familiar with the first gen but I believe the knock sensor isn't that important. But you'll need to replace it in order to get the codes to clear and only illuminate the CEL when the problems arise.

 

[2011Pro-4X-Alex]

My 2011 Pro-4X with ~120k miles is showing code P0420. I could replace the catalytic converters but I'm concerned there could be a larger issues. I've seen posts about the upstream problem being an exhaust manifold or other issues where the catalytic converter just goes bad again pretty quickly. I'm in state that does emissions checks so I don't have many options. I need to either get them replaced or potentially sell the car. Any thoughts or knowledge on what the root cause might be or if it is worth replacing?