I have a 99 blazer LT with 145,000. I bought it a few days ago. When I drove it home the SES light came on (awesome). I pulled the codes.

A total of 3 codes, all emissions related I believe.

P0420 catalyst system below threshold bank 1 (this code came up twice)

P0133 circut slow response bank 1 sensor 1

I've read the tech articles for these codes so I have a basic understanding of what it could be. The converter isn't making any noises. The truck does seem to have a very slight stutter or hesitation when at idle but it isn't very repetitive.

I guess I'm asking you fellas where you think I should start? How do I know for a fact the o2 sensors are bad or the cat converter is bad?

More importantly, what causes it? And how do I stop it from happening. There's a really good chevy dealer where I live, I may take it in and have them do an inspection/diagnosis on it.

Thanks for your help.

Mack