96 lumina Code P0420

Took car to Auto Zone and they checked for codes,came up P0420.The print out read that the Catalyst system efficiency for bank 1 is below thresholdfor the current engine conditions. (Bank 1 identifies the location of cylinder #1,while bank 2 identifies the cylinder on the opposite bank).Still seems to run ok,could it be some kind of sensor? Thanks Alot,

What has happened is the catylist has lost its efficency.
If you have less than 80000 on your car, take it to the dealer....the converter is covered under warranty for 8 years and 80k miles...replacement is no cost to you.

Thanks GM, I guess I'll have to take it to Dealer.Thanks again,, Car has 96,000 miles on it.

yeah...my 99 just started throwing this same code and like a dummy I just started changing oxygen sensors needlessly because I didn't really take the time to try and comprehend "catalyst below threshold", when it mentioned "bank 1" I automatically assumed that it meant the oxygen sensor before the converter was bad itself. Than, to further demonstrate how little I actually think about things... I changed the oxygen sensor after the converter thinking it was the problem. Then I kept wondering why in the world my check engine light kept coming on. I'm about to put a higher capacity universal converter on my car. Anyone have any problems doing this? I'm hoping to get a little more power as well as better fuel mileage... atleast that's what I was told would happen. It's a shame cuz I only have 65,000 miles on mine but I'm a second owner.

I'm about to put a higher capacity universal converter on my car. It's a shame cuz I only have 65,000 miles on mine but I'm a second owner.

Your bad cat is covered under EPA mandated warranty even though you are not the original owner!
The CAA(Clean Air Act) requires an 8-year or 80,000 mile warranty on the major emissions control components such as the catalytic converter.

I have a 97 3.1 and I had that same code come up in my obd 2 diagnostinc tester and I had the cat replaced for 290 dollars and the code instatnly went away.