[BillG]

I assume what you mean by "bad engine performance that is over-saturating the cat" is that the engine is running overly rich and/or misfiring. These running conditions will throw a different code than a low catalyst efficiency code. Furthermore, either condition will cause the the cat to overheat and can/will cause catalyst substrate to meltdown and plug-up in short order (in other words, the cat is destroyed), that is why the CEL will flash when this condition is encountered. P0420/P0430 codes are almost always caused by one of three things, a bad O2 sensor, an exhaust leak, or a worn-out catalytic converter.

Overly rich OR overly lean can cause poor combustion. Misfires happen more or less constantly in cars, less often when new but getting more frequent as various parts/pieces wear out. If you watch live misfire data on a brand new car, you'd probably see 3 or 5 misfires on each cylinder over an hour of driving. But those won't throw a code. Between a random one-off misfire and the potential for false alarms is why the misfire code only triggers for a certain number of firing cycles (revolutions). There are 2 or 3 different thresholds and only one will cause a flashing CEL (indicating misfires more or less constantly). And, yes, that CAN saturate a cat and throw efficiency codes AND misfire codes. Usually, though, fixing the problem and then driving at highway speeds will burn off much of the saturation and clear the code. Not always, but often. Otherwise, something like a leaky injector would be an $8k repair.

I would argue that P0420/P0430 codes are almost NEVER thrown from a worn out cat, but can result in a bad cat if you ignore the root cause of the P0420/P0430. But the common thing when you go into a shop with a P0420/P0430 code is that they say you need a new cat, and, $2000 later, the code is gone. Then, a few months later, you go in with some other code (p0300, p0171, etc.) that has manifested as the issue got worse and they fix the ACTUAL problem for another $600. OR, like me, you get a P0420 and hope the actual cause is that your cat-back exhaust now identifies as swiss cheese and hope the problem goes away when you replace it this weekend!

 

[BillG]

Thank you guys both for your insights! Reading your replies brings up a new question for me: I am getting both p0420/p0430 errors, so it’s both banks that are throwing a code. In my mind, it seems unlikely that both O2 sensors would go at the same time, indicating replacing 02 sensor may not be the right move? Would you guys agree with this or not? Also, I’m thinking it wouldn’t be an exhaust leak because why would a leak in one location influence both Bank 1 and bank 2? Any thoughts? Thanks!

Exhausts are funny things... Back in the day, they used to design them for as little backpressure as possible. Now, they realize with sound and emissions considerations, they will always have some backpressure, so they take that into consideration when designing the system. If you punch an exhaust hole somewhere and let gasses freely escape, the flow can change and trigger codes. Additionally, the fact that one part of the exhaust rusts through probably means other parts are just as bad. So, while you might not think a hole in the muffler flange could trigger the codes, the small leaks up in the front Y-pipe certainly can.

You didn't say you have an exhaust leak, but you are questioning if that could cause the problem, so I'm going to guess you have an exhaust leak. If this will be DIY, you can certainly fire the parts cannon at this thing but it's usually a better option to try to diagnose the issue first. If you have known issues (i.e. exhaust leak), they have to be addressed anyway, so you might as well do them now to hopefully resolve your issue. As for the original question of if changing the PCV will fix your codes, the answer is probably a 'no.' But, then again, it might. But so might changing the air filter or the timing belt or the fuel injectors or the O2 sensors or the cats or any other number of things. Replacing the cats is just the most expensive version of parts cannon that you can get.

 

[Jlancehi]

It is possible that both O2 sensors have gone bad at the same time. It is also possible that both cats have worn-out at the same time. After all, in both cases the parts likely came from the same production runs, were run in the same vehicle for the same number of miles, and under the same operating conditions. This is not an unheard-of or unusual occurrence.
This reminds me of the member who had both brake lights suddenly stop working (3rd brake light still working). I suggested that the light bulbs might both be burned-out, and that is exactly what it was.

Thank you, that makes a lot of sense and is helpful to hear your experience with that. Now, would love to hear what you guys think about this: if you scroll to 13:30 on this video, you’ll see what i was referencing earlier, where he says after 2004 the computer won’t throw a p0420/p0430 code for bad O2 sensors. Since this seems to be different than what a lot of folks say in this forum, I’d love to hear your feedback and I feel like this also might contribute to the ongoing conversations around these codes. Do you think he’s correct? Or do you still believe my codes could be caused by bad O2 sensors? Pasting link to video here:

 

[wag3719]

Assuming that you have eliminated the possibility of an exhaust leak, there is a high probability that the cats are worn-out (although when you first posted you claimed only a P0430). As Bill has stated, you should make absolutely sure that there isn't an engine problem that has caused this situation before you start throwing parts at it. Also, you should never replace the cats without replacing the O2 sensors, so this is where you should start your repair efforts (after you have checked the other things).

 

[BEEMRDON]

Exhausts are funny things... Back in the day, they used to design them for as little backpressure as possible. Now, they realize with sound and emissions considerations, they will always have some backpressure, so they take that into consideration when designing the system. If you punch an exhaust hole somewhere and let gasses freely escape, the flow can change and trigger codes. Additionally, the fact that one part of the exhaust rusts through probably means other parts are just as bad. So, while you might not think a hole in the muffler flange could trigger the codes, the small leaks up in the front Y-pipe certainly can.

You didn't say you have an exhaust leak, but you are questioning if that could cause the problem, so I'm going to guess you have an exhaust leak. If this will be DIY, you can certainly fire the parts cannon at this thing but it's usually a better option to try to diagnose the issue first. If you have known issues (i.e. exhaust leak), they have to be addressed anyway, so you might as well do them now to hopefully resolve your issue. As for the original question of if changing the PCV will fix your codes, the answer is probably a 'no.' But, then again, it might. But so might changing the air filter or the timing belt or the fuel injectors or the O2 sensors or the cats or any other number of things. Replacing the cats is just the most expensive version of parts cannon that you can get.

I

Assuming that you have eliminated the possibility of an exhaust leak, there is a high probability that the cats are worn-out (although when you first posted you claimed only a P0430). As Bill has stated, you should make absolutely sure that there isn't an engine problem that has caused this situation before you start throwing parts at it. Also, you should never replace the cats without replacing the O2 sensors, so this is where you should start your repair efforts (after you have checked the other things).

I had success recently with 2 bottles of techron. 😎

 

[rangerbentman]

So I see we wandered from the topic a bit! PCV replacement also means a possible hose replacement . Is there a specific part number / description of the hose as I can not find it and my hose is disintegrating near the PCV? Has that 90° corner which puts a wrinkle in a simple straight hose replacement.

 

[paul r]

This "may" be the hose you are looking for your 2008 Sienna
Toyota 12260-31050 ventilation hose

 

[rangerbentman]

This "may" be the hose you are looking for your 2008 Sienna
Toyota 12260-31050 ventilation hose

That one does not have the 90° bend in it. the 12261-does but does not seem to have any covering material.

 

[paul r]

Could it be there are two hoses involved? One for the valve end and another for the "box" end. A pic of the one on your Sienna would help

 

[rangerbentman]

The next time I play mechanic with the Sienna I will see about a picture.

 

[BillG]

By "covering," do you mean the flexible mesh over it? I always just slid that off the existing one and awkwardly slid it on the new hose, like a finger trap.

 

[paul r]

On ours BillG, the covering is like a dense foam tube .

 

[rangerbentman]

Yes I have that fluffy foam tube covering it as well. There is something you can buy to bend rubber tubing to conform to what is required or just buy it from the Toyota dealership at a higher price/

 

[FremulousTremmel]

I thought this was a great idea (to move the INTAKE AIR CONTROL VALVE ASSY NO.2) and went to look and now I'm wondering how on Earth you were able to access and loosen/remove those 3 bolts and the nut? Especially the bottom one!? You can't even see it nor get a tool in there to ratchet it loose.

 

[rangerbentman]

Look up " The car care nut" on youtube and add pvc valve . He specializes in toyota. My pvc is out in the open on my 3.5 liter whereas yours is hidden

 

[rangerbentman]

I thought this was a great idea (to move the INTAKE AIR CONTROL VALVE ASSY NO.2) and went to look and now I'm wondering how on Earth you were able to access and loosen/remove those 3 bolts and the nut? Especially the bottom one!? You can't even see it nor get a tool in there to ratchet it loose.

 

[FremulousTremmel]

Look up " The car care nut" on youtube and add pvc valve . He specializes in toyota. My pvc is out in the open on my 3.5 liter whereas yours is hidden

Yea, that video could be helpful for my Venza which has that engine, but the Sienna doesn't so it not the same accessibility, unfortunately. Cannot understand why it would be designed to make something that is replaceable and needs to be cleaned so impossible to remove easily.