I’ve been hit by tge P0420 code at 200k miles and 24 years of age. Not bad, not bad. I started with replacing the front air fuel sensor (sadly I have a Cali emissions vehicle) and the rear O2 sensor hoping it was just tired sensors. $300 later and that didn’t cure my CEL, it came back about 200 miles later.

So, I don’t think my cat is complete junk, yet. But I know it doesn’t have much life left. I’m going to have to replace at least the upstream one to start. Also I don’t live in an area where I’m likely to get mine stolen and have the insurance solve my problem.

mcgeorge has an OE Cat for $1k. Rockauto has aftermarket cats from Walker and Davico for about 1/3 of that. Has anyone used aftermarket cats with good success?

 

I replaced my oe cat with a Walker in 2013 at around 248,000 miles, so far so good at a smidge under 330,000 miles. Pinging, loss of power on hills. No code, but very little makes the 96 throw a code.
Will it last as long as oe? I'll keep seriously doubting it unless it actually happens.
96, cali emissions, 3.4 m/t, single cat.

 

I put an O2 spacer on my '99 a few years ago and it has passed testing twice since then. Runs fine, no codes, Might be worth looking into.

 

I believe I bought a Walker cat from RockAuto, too. I remember my mechanic saying not to go too cheap, but that it didn't need to be OEM. His opinion, of course, but he's not your typical mechanic and I trust his opinion on parts. But I never got a specific answer on what qualifies as "not too cheap". The Walker isn't the cheapest on RockAuto...

I'm not a great mechanic, but I had trouble (posted about it here) with the upstream connection. Could never get the flanges to sit flush, and could see the gasket moving around in there. Finally had a muffler shop weld both ends. Solved the problem. I've had a check engine light come on & off here and there but I don't have a scanner and so far I've ignored it. Last time a check engine light came on and stayed on long enough for me to borrow a scanner was a lean condition code. No idea if my current off & on light has anything to do with the cat, just figured it's worth mentioning.

So while I can't say "the Walker is great!", I can say it's worked so far...Maybe I've put 40,000 miles on it? But without running a scanner and interpreting everything, I'm not sure I'd notice whether a cat is working great or not. I'm absolutely sure it won't last as long as OEM. For me, on a truck w/ 325,000 miles, I make some compromises. I'll never put crap parts on my truck, but does a new part need to last 200,000 miles? Probably not...