P0420 After Valve Cover Gasket Change

Well here we go again, started on the “correct side” bank 1 sensors. Got the downstream one replaced with the one I pulled off bank 2 side. When I got to looking at the upstream sensor it was obvious that it had been recently replaced by the previous owner. It didn’t appear to be a Denso, instead of the gray protective it was blue, not saying that Denso could have used blue. Just wondering if it could be a cheapo sensor causing the code to be thrown. Anyway I was going to change it with the one I pulled off bank 2 but for the life of me I could not get it disconnected from the plug….I tried for 2 hrs but was unsuccessful…it really needs to be on a lift in order to get both hands on it. Right now I’m frustrated with it and going to give it a rest and watch some football. I did rest the code…will see what happens with replacing the downstream sensor….more to come.

 

I'm not pleased with the NAPA front sensors in mine but was in a pinch at that time. I now have OEM from Toyota Dealer ready to go.
All that to say, yes fronts are a bitch for me but I have decided to remove tire and what I'll call the rubber Engine Aprons when weather is more conducive.
Supposedly we can access it better, we'll see.

Watching football sounds better tho....Go Chiefs, since Titans suck again this year !

 

Yea, I thought about attacking it from that side too..will let you know how it goes.

 

Yup, this type of thing is pretty much why folks warn about going non-OEM with electronic parts. It's also possible it's branded "Denso" but is a knockoff because they bought it on scAmazon or fleaBay.

 

3 days since replacing the downstream sensor on the real bank 1 with the old one off bank 2 which I thought was bank 1….no codes thrown….keeping my fingers crossed.

 

Downstream is after the car right? I can never remember. What’s your commute like? I don’t think it would take days to complete the cycle.

 

upstream = between engine and cat (before cat)
downstream = between cat and muffler (after cat)

 

It recoded yesterday, gonna try replacing the upstream sensor with the one I took off bank 2….if that doesn’t work it may be time to start looking at the cat itself. I’m about out of options, gonna go over it one more time to make sure I didn’t miss any leaks.

 

I am not saying it’s never happened but I have yet to find a situation where the o2 sensors are bad and the cat is actually in good shape.

 

Speaking of this Forum only, we've had way more bad O2 sensors being the actual culprit than folks reporting it was an actual CAT when confronted with P0420 code.

What have you done to your 1st gen Tundra today?

 

Yep, what he said ^^

And, honestly, if you replace the cats and it was a bad sensor, and you run with that bad sensor long enough, you'll be buying new-new cats all over again later.

I've seen new O2 fix complaints of 'inefficient cat' more than I've seen it actually being the cat on dual-cat setups.

 

I see, Well I stand corrected then. I definetely should test mine because I am in the same boat with a 4.7

 

I could see the cat clogging if you let it run too long with a misfire/foul or similar situation, but it takes a hell of a lot to clog a cat, and you need to have a problem for a decent amount of time, unless it's super-serious, in order to clog one up.

Granted, I personally know a lot of guys who for various reasons, choose to ignore CELs. Like, they're catch a CEL, and don't like the code associated, so they ignore the light in the dash. Then, when another issue pops up, they have no clue it happened, and that's when things snowball. Most who're in that camp are anti-emissions guys who'll pop for an O2 sensor and do just that: "screw it, ain't gonna let them treehuggers own me, truck runs fine!" and just live with the light in the dash, that's when worse things happen.

Cats aren't inherently prone to clogging, it takes quite a bit of abuse. Generally speaking, you should set some kind of code that gives you a heads-up something is wrong and needs correction. If you perpetually ran absolute garbage gas every tank, for example, I could see it happening. But you're likely going to get a knock sensor code like I did recently before you see misfires, O2 errors, cat efficiency errors.

Regardless of the above, there's always a corner case. The corner case could be you. It's just been my experience, cat efficiency errors are usually less often the cats themselves, and more often a failure or degradation of the sensor responsible for monitoring cat efficiency, or something causing the sensors to read "off" (leak, etc.)

 

Makes sense, my situation for sure needs more investigating but I can’t help but feel like I am high jacking OP’s thread so maybe I’ll start a post of my own and hopefully with the help of all of you I can figure it out. Anyways is there any hope for OP? How about checking the values of the upstream o2?? Or changing that one entirely on the correct side. Not sure if you have done that already I assume you’ve only change the downstream on the correct side.