P0420 code with some history
 

Hi everyone, new here so sorry if I dont include important information...

A month ago I had my check engine light come on so I went down to my local autozone and spoke with someone there and had the codes pulled. It was p0420, autozone lists some probable causes with their code reader and speaking with the autozone people and some friends the assumption was that as the car should have the o2 sensors replaced (130k miles now) we should start with that.

Since replacing the upstream and down stream o2 sensors the cars performance is inarguably better, but after a day of the check engine light being off now its back on. From a lack of car savvy, i decided to reset my battery again and see if the light comes back, which it did. I took it back to Autozone and it came out with the same code p0420: catalsy system efficiency below threshold bank 1.

probable causes: a/f ratio, air leak near h02s (heated oxygen sensor) bank1, ignition system concern & faulty cat converter.

Searching through the forums here I see that the code generally pertains to the cat converter, is there anyway to confirm this? I have heard that in general issues with the catalytic converter tend to be very obvious. Also I have seen the de-fouler/anti-fouler setups, but dont trust myself enough to do that. Are the o2 simulators a good way to go? I'd be worried about missing future issues in using a simulator.

As far as I can tell there are no issues with my car at the moment in terms of it runningn, no noises or odd behavior. Its a civic ex 02 1.7L. Just replaced both o2 sensors with Bosch brand universal fit sensors (saw another thread about OEM sensors still throwing the same codes?)

Thanks a lot ahead of time.

Brian