Pesky P0420 code Techstream freeze frame data

I have a 2006 Tacoma, 4.0 auto and have owned it since new, approx 130k miles. A couple years ago I had a P0420 and I think I remember changing the rear 02 sensor and it went away. But it has come back recently and continues to come back when I clear the code.

I have a copy of Techstream and just started wading through it. I went back through a number of old posts about the P0420 code, the A/F sensors and how everything interacts with each other. I also have the ES-212 SFI System portion of the service manual with the steps necessary to test the A/F sensors. While I was getting up the courage to do the test, the P0420 code popped back up. I went into Techstream and pulled up the freeze frame data and that is below.

I've read about the ST Fuel trims and how those affect/are affected by a clogged cat or bad sensor, but I need to research it more to gain a better understanding.

But before I do that, does anyone see anything that stands out to them that would point to why it's throwing that code? Like I mentioned before, the big difference I can see is that my ST Fuel trims are not similar between B1 and B2. That's telling me something, just not sure what.

 

Having the same code with my 05 Tacoma V6. My data is from the OBDLINK software and I don't know what the numbers are telling me either. Hopeing someone will chime in and put us on the right track to solve this mistery.

 

map both the bank 1 af sensor and bank 1 o2 sensor in graph form then under active test use the fuel lean/rich test. When using the test if the rear o2 changes at the same time the a/f sensor changes then you need a cat.

 

Great, I'll try that, thanks! I was a little apprehensive about doing the test, not really knowing what little details to look for. I'm going to go ahead and do the test tomorrow but earlier today I checked the resistance in the B1AF according to the following chart and between 1-2 I had a reading of 2.9 ohms but the 1-4 test resulted in OL (open?) so I ordered a AF sensor that should be delivered tomorrow. I want to confirm that diagnosis though and I'll run the lean/rich test tomorrow and see what results I get.

Thanks again @stefanlg55

 

If I do have to change the B1 cat, it seems like the easiest way would be to remove the passenger front tire and that rubber flap covering the gap behind the shock. I did this to access the B1AF sensor connector and the manifold bolts are right there with easy access, or so it seems.

 

If you have to change the cat you already know the are $$$. If the honey comb is not broken inside before I spent the money I would first do the cat wash rehab for only a couple bux. If you get that far tag me or pm me for the procedure.

 

Yeah, I looked them up earlier today, not cheap. Thanks for the offer, I'll hit you up if I get to that point.

 

I just ran the rich/lean test and the ranges look to be ok? Test was rich first, back to 0, then lean. @stefanlg55

 

I've checked these values with the values from the chart and if the sensors have readings within the acceptable ranges, you look to either an exhaust leak or the three way cat.

Does anyone know if I can confirm the diagnosis of a bad cat by looking at other data, like short term fuel trims? My B1 STFT seem to always be higher than B2 outside of the test.

 

I got under the truck this morning and I found this exhaust leak, it's after each bank comes together. Is this enough of a leak to set the code?

 

This just keeps getting weirder. I took the exhaust apart at the connection where it was leaking, moved things around a bit, took a rag and cleaned the connection up. Reconnected everything and got in the truck to move it back and the CEL was off. Huh. Took it for a drive and just using my bluetooth app the P0420 code was active, but no light. I didn't clear it and just exited out of the app. I get home and check it again and the P0420 code is pending but still no CEL light. I think it takes two driving cycles to set the code but, wtf????????

 

the a/f reading you took are stating it is good. your 2.9 ohms is within range and the 1-4 should be over 10kohms which is open. That is correct.
The exhaust leak you found is fine because it is after the secondary cats and 02 sensor, so the ecm will never know its there.

According to the rich lean test its showing that your cat has failed. As you can see from the chart when you switched to rich both the b1s1 and b1s2 switched at the same time, You should see a delay with the oxygen sensor as it take a little for the cat to filter out any emissions. The lean part of the test is not really necessary as you are starving the engine of fuel so the 02 wont pick is up as much.

So it looks like you need a cat. Although just to be on the safe side make sure that your engine has been warmed and your 02 impedance is low you will see it drop from 20000ohms to i wanna say less then 200ohms. once that is under 200ohms you can perform the test, that will make sure your 02 sensor is within its heat range to properly monitor for nox. If you would like also perform the rich test on your other bank and you will see a delay so use that as a comparative test to your bank that is setting a code.

Yes cat codes are 2 trip conditions so it will come back as as pending code on the first trip before it become current code (check engine light) on the second trip.

 

@stefanlg55 thanks a ton for breaking down that test. I'll rerun it as you suggested and confirm. I looked at a stock replacement on rock auto and it's not too bad price wise. Install doesn't look too bad either. Thanks again.

 

Not a problem, let me know how u make out with confirming it. Just try and do research when you buy the aftermarket ones seen a few fail very short of there lifespan.

 

Nice job..

 

@stefanlg55 Am I interpreting this correctly?. I wasn't sure how to gauge the impedance of the 02, so this morning I took the truck for about a 20 minute drive to make sure everything was good and warm. Arrived home, hooked up the laptop and ran the active test from rich to neutral and here's the results.

Here's where I'm confused, it seems everything switched at the same time when I ran the rich test.



Unless you are referring to when I switched it back to neutral and it looks like 02S B1S2 (dashed magenta line) was just ahead of 02S B2S2 (solid orange).



Here's the same data with the both rear 02S dashed so they are easier to see. Is this the immediate switching? the difference in the dashed lines where the dashed orange (02S B2S2) is slightly behind the dashed magenta (02S B1S2)?

 

I'm on hold on the cat at the moment. I'm not understanding the diagnosis and need to do more research. But, the Check Engine light is still not on and the P0420 code is current. I thought the check engine bulb burnt out but it comes on when you initially turn on the key. So I dunno, never seen that before.

 

If you have a p0420 code you need a cat. I’ve never seen a single instance of a 420 code lying.

 

That is odd sorry its been a little while since i have had a cat code.
Don't worry about the 02 impedance i was talking about i don't believe that pertains to your vehicle. Although in the test you posted it appears you were at neutral then went rich and then lean. You might want to run the test again this time just let the truck idle for about 10mins to heat things up.
Just graph the 02 sensors and go neutral, rich ( wait for the 02 sensors to respond ), neutral and lean.

 

@stefanlg55 I'll rerun the test but it was plenty warm. The test tells you to keep the RPM's above 2k, so that's the first horizontal line in the screenshots above. When I hit the +12/5% button and run the test, that is the big drop. But, both sides switched at the same time, there is no lag. I'm wanting to learn how to read the graph, and I'm stuck on when you said there should be a lag and that's how you tell if the cat is bad. I'm not seeing it but I don't know what I'm looking at.