Been searching on here the last 30 minutes. CEL came on yesterday at 98899 miles. Trucks running fine, idles fine, no rotten egg smell, normal gas mileage, no noises from cat. Of course, dealer says I need a new cat. with parts and labor around $1500. 1300 just for the part. I live in MO and think the truck was an Indiana vehicle. They cleared the CEL and Im sure its going to pop back on. I asked them why on earth would a cat just go out of the blue with no symptoms and how do they know its not an o2? They say the o2 would throw a differnt code. Mind you, the truck was never brought in the garage, they just hooked the reader up as I pulled in. We have inspections for emissions in MO and mine is good for 2 years but will need to be adressed and I dont like driving around with a CEL because Im anal. Just passed emissions last month! Any aftermarket cats this vehicles OBD2 will accept? Change o2 sensors now? No idea if they are original. Its a 2000 3.4L with almost 99K

I don't have time to look at the moment, but IIRC the 1st step in the FSM for a P0420 code is check the O2 sensor. Cat is like 4th or 5th on the list.

I saw something of that nature on the search. Check for leaks, #1 o2, #2 o2, cat or something like that.

wow 1500 to replace a cat??!!! o man that sounds scary. i thought it was like 300 or something

You can have your O2 sensor measured for it's performance....I don't know much about it, but when mine threw a code I had it checked out and the service guy hooked up a code reader that showed the O2 sensor readings. It read zero on one of them. I found one on ebay for 40bucks put it in myself and worked perfect. Never had a problem since.

Double if you live in CA

I get a P0420 occasionally on wet days. I clear the codes and I'm good till the next time I hit a decent sized puddle (or mud pit).
Clear the codes and see if they come back.

you can always buy a aftermarket CAT cheap as 150

What I've done to cure my P0420. Still hasn't come on. I really wouldn't listen to the dealer.
From this thread. yet another p0420 question.
I've had the same P0420 problem since when I purchased mine. I pretty much ignored it during the entire summer, however I'm beginning to sort it out. Here's what I've done.
1.) Change oil, (duh, but follow me here).
2.) BG 44K <-- didn't see that it did a whole heck of a lot.
3.) Cleaned the MAF sensor.
4.) Change the spark plug. Replaced with OEM spec NGKs.
5.) Change the PCV valve.
6.) Ran Lucas Oil fuel treatment.
7.) Cleaned the throttle body. Be careful here you might have an idle problem after you do it.
After all of this I've not have the P0420 in quite some time.
-Point being this that it could very well be the case that the engine isn't running as clean as it can be. My advised would be to exhaust all the cheap preventative maintenance problems then work your way to replacing the 02 sensor or a/f ratio sensor. <--- found of the CA model, that is a/f sensor then 02 sensor after the cat.
-I've got a 02 sensor (OEM) which I'll install once/if I get the P0420 again.
-And my truck is running a heck of smoother and cleaner.

Well I did go through a underbody blaster car wash about 2 hours before light came on.

As far as AFTERMARKET cats....has anyone bought a direct factory replacement that the OBD2 was happy with and kept codes clear?

At this point Im getting ahead of myself. No way am I going to mess with cat until I try o2 sensors if the code returns and I have 2 years until the next inspection. Just want to be squared away.

May be something getting wet the same as me. Start by clearing the codes and see if it comes back. 10 bucks says it doesn't.

Its cleared and I set Trip Odo to see how long it stays out. Hopefully for good. If not, o2 sensors will be checked.

I just had emissions a month ago and it passed. Any of you guys know if these numbers can help me decipher if o2 sensors are good? Its all Chinese to me.

Just an update on the thread, the light originally stayed off for about 320 miles. Came back on, had it cleared and came back on like 30 miles later. Stayed on for about 150 miles and today its gone on its own. I have a code reader coming in the mail so I will be able to clear it on my own if and when it comes on. The local Meineke, who I have had a great relationship with for over 10 years said they can put a direct fit, not universal cat on it for like $580 with labor if I ever go that route. Not sure of the brand, maybe CATCO. Will be warrrantied. I hate emissions BS. My 4Runner runs great. No cat rattles, funny smells and now my gas mileage is up to close to 20mpg!

so i shop is gonna charge you almost $520 in labor to weld this on?...it prob won't even be welded but clamped...

Catco Catalytic Converters 6905 - Catco Catalytic Converters Universal Catalytic Converters - Overview - SummitRacing.com

i would find another shop....i think $100 would be on the steeper side of reasonable to weld this piece on.

this is only $210...if you have basic tools you could do this on your own.