P0420 is it always a bad cat?

You can definitely drop the tank without removing the bed. Removing the bed does give you easier access to all of the hoses and connectors though. If your truck has lived in the rust belt for any amount of time it's pretty likely you'll have to replace the straps. That was the case for me at least

 

Now when you replaced your gas tank, were you able to find a complete parts list for all the hoses that were required and the new gaskets and seals? I can probably find them online if not.

 

I used the parts diagrams on partsouq.com for reference, but these were the hoses and gaskets I used. There are a few other evap hoses that can be replaced with fuel line, the two pictured below were formed hoses, so I wanted to buy the OEM part.

 

Awesome, thanks. I'll start collecting all the parts I guess. I'm hoping that defouler will keep the O2 sensor fault away long enough to pass emissions.

 

My engine light was on and that code popped up. I changed my spark plugs, air filter, oil, and oil filter. I drove it around for about 100 miles and the check engine light turned off and I passed smog. 1997 Tacoma

 

Thanks for all the info posted here, very helpful.

I live in CA and have a 2000 3.4v6 4x4 manual with 401,000 miles with a persistent p0420 code. If I clear it, it comes back in about 500 to 1000 miles. Cats were replaced with aftermarkets at about 240,000 miles. Then replaced the rear one again at 280974, due to it having issues. (code p0420). They chased an exhaust smell in the cab for a while, finally getting rid of it. My wife said she could still smell it faintly, however.

Other replacements:
Mass air sensor at 383889
Vac hose 378052 (p0171 code)
Rear O2 sensor 344564
Lots of general maintenance all through its history, I've had it for 380,000 miles.

I just got a quote for $3500 to replace both cats and O2 sensors. I need also to do a timing belt change, with the usual work associated with that. Probably looking at $5k to $6k for all this. Truck runs FANTASTIC and is otherwise in good shape. But it won't pass smog coming up in June '24.

Any thoughts on whether something else than the cats might be throwing the p0420 code? I'm hoping to not need to put 5-6k into a truck that runs great.
Thanks for any help!

 

That is strange that it comes back after being cleared for so long. My P0420 code would come back within 10-20 miles everytime I cleared it without fixing the problem. My issue was a leak between the rear cat and rear O2 sensor. If you haven't done a leak test yourself I'd suggest that. It also sounds like you should try replacing your air/fuel sensor before the first cat if you haven't tried that. Do you have a bluetooth scanner where you can look at live data to see what it shows?

 

Thanks, I'll try a leak test. I should also get a bluetooth scanner like you mentioned. Do you recommend a certain model?

 

I splurged for the Bluedriver bluetooth scanner (~$100) but you can get ones for around $20-30 I believe.