PO420 code

I'm at my wits end with this damn code. Came on about 3 weeks ago. Took it to Toyota found out that when I bought my truck a little over a month ago it had after market cats on it. They replaced both cats and the o2 sensor under warranty. Well earlier this week it came back on, took it back to them and they said it might be the AF sensor. They replaced that. Came back on again tonight. The Toyota guys are trying to tell me that no factory Toyota cat can go bad that fast so they won't even look at that. They are trying to tell me it's my aftermarket muffler (I have a Flowmaster 50 welded on with the pipe dumping after my rear axle). I just don't see how that's possible since it's after all my sensors. What could possibly be happening? I think it's a faulty cat but I'm not sure what other possibilities there are.

 

Here is what you can look at.

http://www.customtacos.com/tech.old...06toyrm/06toypdf/06rmsrc/rm2006ta/0050034.pdf

 

So what is this telling me? I know what the po420 code is I just don't know what could be causing it since they literally replaced everything having to do with my cats.

 

You said above they replaced the cats and the O2 sensor, did they replace both sensors? Check and make sure they are plugged in correctly, You can troubleshoot the sensors with the link I gave you. You could also have an exhaust leak, running shitty gas. This is covered in several other posts I'm just summarizing it.

 

Where is the second one? They replaced the af sensor and the o2 sensor after the cat. If the exhaust leak is after the cat could that cause it? Could Ethanol content of 10 percent cause it? The link was a bit too technical for me and I couldn't understand some of it. I was also half asleep at the time

 

02 sensors can cause p0420 but its rare, often p0420 triggers because the sensors are working and correlating too quickly upstream and downstream.

It's true the its rare to see a OEM cat fail that fast, I've seen aftmarkets fail quickly but never an OEM.

That said, there might be another cause for the cat to fail that isn't triggering another cod

Often cats fail due to misfires, overfueling, richness etc. I've also seen bad fuel kill cats.

If it were me and I verfied the cat has failed (bank 1) I'd look at how the 2nd bank is doing, if its ok then I would look at factors on the bank 1 that could cause premature failure. A leaking injector is easy to diagnose, often you just need to remove a plug and cycle the pump.

 

I'm not very mechanical. I've never had anyone teach me how to do these things so I don't trust myself working on my only means of transportation. I feel like I would know a cylinder misfire if it were happening. It happened in my GTI but this truck doesn't seem to be doing that. I'm not sure where else to check. The dealership basically told me that since they replaced both cats and both sensors that it would be my muffler causing it, could that be the case?

 

Muffler doesn't throw that code. Toyota probably doesn't want to work on it. That link is the guideline on how to find your problem. Since you have new cats and o2 sensor check out all the related sensors that are mentioned in the above link. You might have a dirty maf sensor. Plug a cheap obdii reader in it with torque app. Could be throwing that code because something else is the cause.

 

I've plugged an obdii into it and it reads po420 bank 1 below threshold so that link basically tells me it's either the af sensor (been replaced), the p2 sensor (been replaced), or the cat (been replaced). That's why I'm so confused here.

 

Cool you have an obdii. Check out your long term fuel trims. If it can log or remember highest valve your trim should be under 10% plus or minus. You might be having a fueling issue that your cat can't keep up.

 

Short term fuel trim should be under 10 percent too.

 

Sorry I actually don't have one. A buddy of mine does but he's out of town this week. Will the stored data show on the obdii. I wouldn't be able to remember, I've only had the truck about a month

 

All good. See if you have a buddy you trust to help you look over your truck. Do all the stupid stuff like a fresh tank of gas from a good top tier station. Run some injector cleaner. I have a feeling it is a fueling issue since we can rule out cats and o2. Watch a video on how to clean your maf sensor without damaging it. Check your air filter.

 

i have had numerous 420 codes that had no apparent reason except fuel quality

in these cases i just kept resetting the check engine light until the fuel was gone and the light stayed out

i never replaced any cats or o2 sensors

01 sienna for about a month this occurred and a 00 subaru same thing and at the same time with fuel from stop and shop

that was years ago and no bad cats, o2 sensors or any indication of bad running or symptoms, just the 0420 code

reset it after a few tanks of fuel from another source

Steve

 

Haha I just filled up which sucks. Yeah gas around me has a high Ethanol content and since I'm in a small mountain town I don't have many choices but that might be what's doing it. I've read that anything at 10% or above can throw the code. I'll check the air filter. What's a good injector cleaner to use?

 

This will likely be what I try.

 

I got this code...pissmeoff. Sunoco ultra and Chevron techron fuel system cleaner... I'm thinking I got a leaking injector based on the smoke I see when starting the motor cold. May swap O2 sensors around as torque is showing bank one, sensor 2 all over the place while B2S2 is pretty much a flat line

 

Yeah finally fixed mine. I cleaned the MAF sensor and then saw that whoever changed the spark plugs the last time did not properly reconnect one of them so I think my fuel was running too lean. Now that we did all that it's been a couple hundred miles and no light!

 

I chased this for over a year on my '06, finally checked wire continuity to the computer behind the glovebox and sure enough it was a corroded wire in a clip on the side of the trans. Of course after buying cats, 02 sensors!!
Find the pin out for the computer and 02 sensor, disconnect both and use a multimeter to see if there's continuity/resistance in the wire. you'll need a long piece of wire or really long leads on your meter to reach both ends.

 

It seems to run OK. I am not feeling a misfire or dead cylinder. Here are some screenshots from torque