O2 sensor or bad cat?

I have a check engine light on my truck my only question is how can I tell if it's my catalytic converter or just a bad o2 sensor cause my check engine light didn't come on till my back cat went bad so thinking it may be a bad o2 sensor?

 

Sorry bad with punctuation.

P0430 is the code it's saying, it's saying the catalyst is below threshold.

I know the rear cat is bad cause the baffles have busted and was making a terrible rattling initially. Now some days it will other days it won't.

 

So the downstream would be the 2nd sensor between the 2 cats?

How do I test the upstream 02 sensor?

I have an 07 Tundra 5.7 with 173,400.

 

Jason's right on, 430 is a cat code. Means the downstream sensor is not showing that the cat cleaned up the exhaust content that the upstream sensor saw... put a cat in it.

 

So just replace the bottom cat then?

 

U have 2 sensors on each side right? There is a cat in between the sensors or 2 cats I'm between? What ever is in between the sensors is what the ecu is "monitoring". That is what failed the test causing the p0430.

 

Okay, so it's probably one closest to the block then more than likely. And then I would guess that being the front one went bad it caused the rear one to go out too?

 

Could have yes. The cat downstream from the second sensor is only there as a backup to cleanup the exhaust more for the ozone... it does get tested during an e test

 

Well this might get pricey unless I can sell 2 and get my 1 replaced haha but it possible to just get the top replaced and rewelded without having to take the manifold off?

 

Hahahaha I said u were right!!!!

aren't they in a different pipe section? Not sure about what an exhaust shop could do. I will leave u with no aftermarket cat will perform like an oe

 

Well for mine is the passenger side which has the bad cats, there all on the same pipe just about a foot between them. Yeah if anything I'll put aftermarket on the 2nd ones mainly for sound.

 

Well I want to have at least the front fixed for the fact I can tell it's actually killing my mpg, not that I bought it for that but would like it fixed.

That's another thing we have emissions but not sure if my cousin will check me for it, because if he doesn't going to cut off the rear 2 cats.