On my 2006 4runner V6...

Hey guys so for while now i've had a CEL. The first time I took it to autozone i got these codes: p0420, p0430, and p0456. After some research i found an exhaust leak could be the issue. And a couple months ago I took it to a muffler shop to put a flowmaster muffler on so I thought there might be a leak from that. So my buddy and I took off the cat back and there was, in fact, a couple leaks where the new muffler was attached. We welded them up and put it back together. Then i unplugged the battery to reset everything and drove for a couple days and they came back on. Took it to autozone and the exact same codes still. So i'm not sure if its an o2 sensor, still a leak somewhere, or worst case scenario gotta replace my cats.

Any ideas?

Couple things that may be worth noting i've replaced both the rear exhaust gaskets within the past couple months and only intake mod i've done is a charcoal filter delete

Also the p0456 - we've had this one before and replaced the gas cap and it was off for a while but now back on so not sure what it could be either, more concerned about the cats though

p0456 is gas cap related....replace with new gas cap and clear lights.
p0430 and po420 are related to the downstream oxygen sensors....either remove them , soak and wash with toilet cleaner or add spacers to the sensors..if emission testing isnt needed in your location

Your profile says "Folsom" - is that Folsom, CA? If this is the case, you won't be able to use spacers or any other inexpensive emissions fooling tricks on the internet as the smog anything will fail anything which does not pass visual and does not have the monitors set on the ECU. Your options are to replace the worn out cats with new cats (p0420/p0430 indicate cats are worn or missing) or try something different.

I have been working on a drop-in modified o2 sensor which appears to be a normal o2 sensor from the outside, but it outputs conditioned signals which advise the computer that the catalytic converters are working normally. I have them in my truck and have been experimenting with their signal levels for months (I had the same o2 codes you do), if you want to buy a pair of them and install them into your truck, let me know.

thank you