P0420 code

Hey all I need a bit of advice. I got a check engine light come up, and after checking it it threw a P0420 Code "Catalyst System Efficiency Below Threshold Bank 1".

I was looking at the following thread, but I have some questions.
https://www.tacomaworld.com/threads/p0420-code.646690/

I've done some research online, and it seems when a O2 sensor goes bad, there is a separate code for it. Specifically P00311 (from what I've read). This code will tell which Bank and which sensor specifically is bad. Since the V6 has 4 O2 sensors. A upper and a lower sensor. I know some people were recommending checking the O2 sensor but if there is a different code for the O2 sensor specifically wouldn't it be throwing that instead?

So I'm hoping that it could be a gasket or something along those lines and not the cat, but how would I go about checking that? Also how could I check to see if the O2 sensor is bad but for some reason it didn't throw the proper code. Also to confirm Bank 1 is the passenger side of the vehicle correct?

I know there's several gaskets on the passenger side so how could I test to see if any are bad, besides visual inspection? Resorting to replacing the cat is the last thing I want to do. Also I've felt no difference in performance, which from what I've read is something you will feel when a cat goes bad.


Note:
2006 TRD Off-Road 4.0L, 233,xxx miles.

 

bump

 

Does it stay on?

 

It's very rare that I see an AFR or O2 sensor as the cause for a P0420, an exhaust leak near or upstream of the AFR or O2 sensor can cause it but don't see that very often either. Most of the time it's a catalyst that is no longer functioning properly.

To understand why the code is setting you have to understand how the PCM monitors catalyst efficiency and the voltage thresholds for an O2 sensor.
Because a normally functioning converter stores oxygen this allows the PCM to monitor their function using the AFR and O2 sensor.

There are 2 methods used to monitor the catalytic converter function:

Downstream O2 switch rate: The PCM compares the rich/lean switch rate of the upstream and downstream sensors under certain driving conditions. (older vehicles for the most part used this method and were relatively easy to "fool" with various methods)

Oxygen storage capacity: The PCM will deliberately force the air/fuel ratio to a rich or lean state under certain driving conditions and measure the length of time between when the upstream sensor switches and when the downstream sensor switches. (almost all modern vehicles use this method or a combination of both methods and are harder to "fool")


A standard O2 sensor generates a 0-1v signal based on oxygen in the exhaust, because they have a very narrow operating window essentially anything above 0.5V (500mV) is rich (<14.7:1) and below 0.5V (500mV) is lean (>14.7:1) although usually the "dead zone" threshold for a lean/rich "switch" is around 0.45V (450mV) - 0.55V (550mV)


The way we check converters and sensor operation with a scan tool is graphing the AFR and O2 sensor data.
It's kinda hard to explain what good and bad data looks like as far as sensor operation but typically with a good functioning cat at operating temp the downstream sensor should stay relatively constant at around 0.7V (700mV).

Here's some known good captures, you can see how the AFR (Upstream) sensors "switch" very rapidly and the O2 (Downstream) sensors stay relatively constant.

First one is an accel and decel event and the 2nd is a steady cruise.

 

I’ve had P420 for a year now and counting.

I just clear the code and move on with my life.

Do I have issues or had any issues?
No.

 

you could plug the tailpipe with a sock & some tape.
spray water from a spray bottle on the gasket areas or stethoscope with just the hose attachments listening for leaks....

I dont know Toyotas per say but ive been replace cats for 30 years for p0420s & p0430s...
Its never an o2 sensor or an exhaust leak on fords, I dont foresee this being any different but some guys like to argue the scenario & nobody ever really gives an update after they claimed they fixed it by repairing a micro exh leak.
its always the cat.

 

Some folks dont have that luxury & theres smog inspections every 2 years.
theres no clearing the codes & smogging it real quick before the light comes back on.
Doesnt work that way monitors will never clear.

 

My daughters 06 would throw 0420 & stay on for a couple days, & then go off. Did that a couple times. Went a while, & then threw 0420 & 0430. Went off, cleared the codes, & hasn’t resurfaced in about 2 months.

 

the issue is still there, it doesnt fix itself,
give it time, it will be back....
under certain driving conditions, monitors take 2 months to just clear.....
When pcm realizes all perimeters havent been met cuz the cats are toast, the light WILL come back on...

 

I figured. Just a waiting game now.

 

Another argument, I know its not toyota, but still....
Guys come on here & talk p0420 p0430 & want to blame it on exhaust leaks....
Ive worked on sooooo many f150 3.5L eco boosts with HUGE exhaust leaks,
Due to the weight of the turbo on the exh man, they can warp well over 1/4", blows me away how bad they warp.
So huge gaps between the head & the exh manifold.
They dont ever throw p0420, or p0430's.....
Yes they do throw cat codes but we never advise them that they have to fix their exhaust leaks to remove the cat code.....

They weekend DYI warrior reads too much shit on the internet & thinks its the Bible....

 

I changed both Bank 1 up and downstream O2 sensors (Denso from Rock Auto) and called it good. I was certain it wasn't the converter because I've owned and maintained the vehicle ('09 4Runner) since brand new. O2 sensors get lazy over the years and many miles.

 

O2 can get lazy...
We always look at the monitoring live pid data & look at O2 saturation %'s of the cat, O2 saturation in itself will tell you if the cat is smoked.
Just cuz you maintained it & are the original owner, even if you never had a misfire, it's very common for cats to just fail. They lose their efficiency over time...

 

I put in some non foulers in the downstream ports. I know it's just a bandaid but it's good enough for me. Light hasn't been back since

 

We don’t have emission checks, so that will be what I do when the time comes. One day, I may get the stomach to give my right leg for new cats.