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Discussion Starter · #1 ·
Does anyone know the Denso part number for P0420 - Catalyst System Efficiency below Threshold Bank 1 . I changed one 02 Sensor a few months back with a Denso but I guess I need to change another one. A picture of the location would be great! I have a 2009. The Last one I changed was on the bottom but the plug was tricky to connect, as you had to reach behind blindlyup top near the firewall to connect it. I left the old wires in place as there was no room to reach in and unclip them. I just cut the sensor off. The vehicle has 220,000 runs fine gets good gas milage, I just getting tired of reseting the check engine light every fill up.
 

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Denso 2344461
Bank 1 Sensor 2
140725

There is a good chance your catalytic converter is clogged at this milage. Replacing the sensor is not always the answer. If the catalytic converter is clogged, solving the reason it is priority.
Start with
Clean Air Filter
Clean MAF
Check air intake tube for cracks (clamps tight)
Clean or new spark plugs
Understanding the risks, I'd disable the VCM knowing the positives of doing so.
 

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Discussion Starter · #3 · (Edited)
Thanks Nail Grease. This helps allot. Much appreciated!!
I'll get started on that list.
Thanks again
I've noticed when the check engine light is on the ECO lamp stops coming on, maybe the VCM is disabled when the P0420 happens. When I clear the CEL the ECO starts working again. Just wondering? My NJK spark plugs have over 100,000 miles, I was thinking of changing them, But I'll check all the things you wrote.
 

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Thanks Nail Grease. This helps allot. Much appreciated!!
I'll get started on that list.
Thanks again
I've noticed when the check engine light is on the ECO lamp stops coming on, maybe the VCM is disabled when the P0420 happens. When I clear the CEL the ECO starts working again. Just wondering? My NJK spark plugs have over 100,000 miles, I was thinking of changing them, But I'll check all the things you wrote.
Our vehicles equiped with VCM are known to be the root cause for emission codes among other troubles. The VCM causes certain cylinders to lay dormant when coasting or in cruise. It causes fould spark plugs, dirty valves and stuck piston rings. Many on the forum are using devices that disables this feature, keeping the engine running on all 6 cylinders 100% of the time. After a few thousand miles, my emission codes never returned.
I use S-VCM.
 

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I was in a similar boat as you and had P0420. It started out sporadic around 125k miles. I could clear the code and it would be gone for a few days to a month. Then it started to come back more quickly. And then it was just there all the time after the 50 mile cycle was up (post clearing the code). After looking at the fuel trims, I guesstimated that the O2 sensors were working fine and the ECU was adjusting the fuel curve as it should, so I didn't bother replacing the sensors. I installed an Eastern Catalytic converter at about 140K and the code has not returned for 15k miles. I do get horrible gas mileage (12-14 MPG, but in hilly Pittsburgh, its HARD to get good around town mileage) so I may try replacing the sensors eventually to see if that helps at all. Good luck!

Definitely get an S-VCM controller. If not, the things that Nail Grease listed above will materialize faster.
 

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I was in a similar boat as you and had P0420. It started out sporadic around 125k miles. I could clear the code and it would be gone for a few days to a month. Then it started to come back more quickly. And then it was just there all the time after the 50 mile cycle was up (post clearing the code). After looking at the fuel trims, I guesstimated that the O2 sensors were working fine and the ECU was adjusting the fuel curve as it should, so I didn't bother replacing the sensors. I installed an Eastern Catalytic converter at about 140K and the code has not returned for 15k miles. I do get horrible gas mileage (12-14 MPG, but in hilly Pittsburgh, its HARD to get good around town mileage) so I may try replacing the sensors eventually to see if that helps at all. Good luck!

Definitely get an S-VCM controller. If not, the things that Nail Grease listed above will materialize faster.
This topic is one of the reasons I ended up on Piloteers. I was searching for answers on reoccurring P0420 and P0430 codes. I replaced my cats, lights out and everything great for 20k miles. Then they returned. Replacing the cat did not solve the cause. The VCM function was feeding my cats so much oil, they couldn't digest it all. Thankfully, by this site, I discovered the VCM disabling device. After 5k miles, the engine light stayed off and has not returned since. I would have had to scrap auction the vehicle 30k miles ago.
 
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Discussion Starter · #7 ·
So I'm getting P0420 rear bank below threshold. So is bank 1 the Cat nearest the rear of the vehicle?? and Bank 2 the Cat nearest the Front of vehicle?? Funny thing is when you get a P0420 or P0430 the code does not tell you which sensor it is since there are two on each bank. Which does not make sense it only tells you the bank.

Since I already changed the lower sensor nearest the rear of vehicle on the bottom which I assume bank 1, I guess I'll change the top on bank 1 now.

Correct me if I'm wrong, the diagram seem to indicate what I'm saying about bank 1 is nearest the rear and bank 2 is nearest the front of vehicle.

I not ready to turn off the VCM yet, maybe someday. Because I'm averaging 21 miles too 24 miles a gallon. Also my plugs have 100 thousand miles so I should change them first but my vehicle runs smooth no other issues.
Maybe since I always used synthetic oil I have not had the VCM issues other have had, since synthetic does not sludge up like Dino oil.

So am I right about the bank locations?
 

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So I'm getting P0420 rear bank below threshold. So is bank 1 the Cat nearest the rear of the vehicle?? and Bank 2 the Cat nearest the Front of vehicle?? Funny thing is when you get a P0420 or P0430 the code does not tell you which sensor it is since there are two on each bank. Which does not make sense it only tells you the bank.

Since I already changed the lower sensor nearest the rear of vehicle on the bottom which I assume bank 1, I guess I'll change the top on bank 1 now.

Correct me if I'm wrong, the diagram seem to indicate what I'm saying about bank 1 is nearest the rear and bank 2 is nearest the front of vehicle.

I not ready to turn off the VCM yet, maybe someday. Because I'm averaging 21 miles too 24 miles a gallon. Also my plugs have 100 thousand miles so I should change them first but my vehicle runs smooth no other issues.
Maybe since I always used synthetic oil I have not had the VCM issues other have had, since synthetic does not sludge up like Dino oil.

So am I right about the bank locations?
P0420 and P0430 codes does not always = bad O2 sensors.
 

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Discussion Starter · #9 · (Edited)
Well it was the 02 Sensor. I guess 221,000 was enough for it. Changed the upstream sensor on bank 1, on top nearest the firewall, no more P0420 check engine light code. Glad it was a easy fix because with that code the VCM stops working and I love my VCM, gives me that good milage. And for those people who like to fabricate stories that you need to turn off the VCM to feel the full power of all six cylinders that is a load of bull. Anytime you push down on the gas your feeling the full power of the six cylinders. It just when you don't need all six cylinders it turns off, like on a smooth highway or going down hill, coasting ect. Soon as you hit the petal you have full power and she goes like a bat out of hell . To me the only thing turing off the VCM does is cost you money in gas. I get a least 20 all the time and a few times I saw around 23 if I did mostly highway.

That said I know other people have experience issues, I have not with my car it runs perfect and my plugs have over 100,000 thousand miles. So not changing a thing.
Thanks for the help on the board.
Fix cost around 70.00 dollars including a 10 dollar 02 sensor removal tool from amazon.
P0420 Catalyst System Efficacy Below Threshold Bank 1
Part Number was DENSO 234-5098.
 

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Well it was the 02 Sensor. I guess 221,000 was enough for it. Changed the upstream sensor on bank 1, on top nearest the firewall, no more P0420 check engine light code. Glad it was a easy fix because with that code the VCM stops working and I love my VCM, gives me that good milage. And for those people who like to fabricate stories that you need to turn off the VCM to feel the full power of all six cylinders that is a load of bull. Anytime you push down on the gas your feeling the full power of the six cylinders. It just when you don't need all six cylinders it turns off, like on a smooth highway or going down hill, coasting ect. Soon as you hit the petal you have full power and she goes like a bat out of hell . To me the only thing turing off the VCM does is cost you money in gas. I get a least 20 all the time and a few times I saw around 23 if I did mostly highway.

That said I know other people have experience issues, I have not with my car it runs perfect and my plugs have over 100,000 thousand miles. So not changing a thing.
Thanks for the help on the board.
Fix cost around 70.00 dollars including a 10 dollar 02 sensor removal tool from amazon.
P0420 Catalyst System Efficacy Below Threshold Bank 1
Part Number was DENSO 234-5098.
At 220k miles and an unbridled VCM, your emmision codes won't stay gone for long. Especially if you haven't replaced your cats. It's a flaw.
The Vtec (VVT) assemblies will need attention eventually.
 

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Does your Pilot burn oil? I typically have to add 1 quart at some point over an oil change interval of 5000 miles. Also, whenever you do your plugs, please come back and share pictures of them. Congrats on your easy fix! I hope it lasts!
 

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Discussion Starter · #12 ·
Does your Pilot burn oil? I typically have to add 1 quart at some point over an oil change interval of 5000 miles. Also, whenever you do your plugs, please come back and share pictures of them. Congrats on your easy fix! I hope it lasts!
Oh yea she burns oil, since the day I got her! No dispute there. You need to be vigilant in watching the oil level. But she purrs like a kitten... I only used synthetic oil since I got her for the last 180,000 miles. I'm getting 20mpg on a very large vehicle, and when I watch the way I drive or do allot of highway, I've seen close to 22 mpg maybe 23. So to be honest I could care less if my Cats go. Will see if Nail Grease is right. As long is she is running fine and giving me good gas milage that is all I care about. Worse case scenario I may have to reset the Check Engine light right before the state emission test which is only every two years. I've never failed anyway.
Gas is not cheap and those extra miles you get with the VCM(eco) add up to hundreds of dollar very quickly if you drive allot. Gonna do the plugs soon I'll post the pictures..
 

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Discussion Starter · #13 ·
Also there are still a few tricks up the sleeve, if the P0420 code comes back. Such as one that usually cost less then $10.00 dollars and still keeps the VCM(eco) working.

It's basically a 02 Sensor Spacer
 

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Oh yea she burns oil, since the day I got her! No dispute there. You need to be vigilant in watching the oil level. But she purrs like a kitten... I only used synthetic oil since I got her for the last 180,000 miles. I'm getting 20mpg on a very large vehicle, and when I watch the way I drive or do allot of highway, I've seen close to 22 mpg maybe 23. So to be honest I could care less if my Cats go. Will see if Nail Grease is right. As long is she is running fine and giving me good gas milage that is all I care about. Worse case scenario I may have to reset the Check Engine light right before the state emission test which is only every two years. I've never failed anyway.
Gas is not cheap and those extra miles you get with the VCM(eco) add up to hundreds of dollar very quickly if you drive allot. Gonna do the plugs soon I'll post the pictures..
A quart loss every oil change is significant. I had a similar issue and came to find out that the Full Synthetic Mobil 1 oil I was using, specifically the Mobil 1 Extended Performance oil had a very high evaporation rate. These vapors must be digested by the catalytic converters, increasing your chances of having P0420 and P0430 codes. My oil loss has been reduced changing to Shell Rotella Gas Truck oil.
 

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Discussion Starter · #15 ·
I use Rotella in my home Backup Diesel Generator the Honda EB12D. It's the best!! I would not use anything else.
My generator is the same as these, I have less then 30 hours on it. It's good for high thousands! I payed 3k when it had 2 hours on it. One sweet generator!! It powers my whole house with the central air running and every appliance and light on, and I still don't come close to using it's output.
I don't know why the guy in the second video has a red can next to his Diesel Generator, Diesel is alway supposed to be put in yellow containers.
 

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I did the O2 sensor spacers in an attempt to get the them out of the exhaust stream. Didn't work at all. I was very hopeful too.

Just food for thought - If your Pilot starts constantly throwing the P0420 code right after you clear the codes, you won't be able to sneak it past emissions once you are up for it again. It needs a bare minimum of 50 miles once the codes have been cleared to be in the "ready" state to be tested. If it doesn't read as "ready", testing place will tell you to go drive more until it is ready.

I look forward to you seeing your plugs! (weird thing to say...)
 

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Discussion Starter · #17 ·
I did the O2 sensor spacers in an attempt to get the them out of the exhaust stream. Didn't work at all. I was very hopeful too.

Just food for thought - If your Pilot starts constantly throwing the P0420 code right after you clear the codes, you won't be able to sneak it past emissions once you are up for it again. It needs a bare minimum of 50 miles once the codes have been cleared to be in the "ready" state to be tested. If it doesn't read as "ready", testing place will tell you to go drive more until it is ready.

I look forward to you seeing your plugs! (weird thing to say...)
Good to know(Thanks) I'm still waiting to see if the code comes back. I will be doing the plugs within the next few months and will definitely post the pictures.
 

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P0420 and P0430 codes are pretty easy to diagnose. Never believe any single item is at fault.
First thing's first... the fuel quality. If you insist on filling up your tank with the cheapest discount gasoline you can find from the oldest gas station in town then I would start filling up from the newest station serving up top-tier fuel. Honda is just one of many auto makers that recommend the use of top-tier fuel in their vehicles for many reasons.
https://www.toptiergas.com/
If you vehicle has been running on fuel of unknown or substandard quality I would highly recommend a quality additive for at least 2 consecutive tank fill ups. Try seafoam, techron, gumout regane, or redline complete, I personally wouldn't trust many of the cheaper products on the shelves.

Next, check for obvious leaks on the intake and exhaust. Next, check the temperatures directly before and after each pre-cat with an IR gun. There are several youtube videos explaining this process. Temp Readings of both cats should be similar with High temp prior and even higher temp after as the cat is doing its job in burning the rest of the fuel vapor in the exhaust stream. The final cat after the 2-1-merge has no sensor to check its efficiency.
If you temp readings look good then it is time to start looking at maybe replacing the o2 sensors. I would do both at the same time given the age - anything over 100k miles would be suspect. Most iridium plugs last about that long so figuring sensors constantly exposed to the same hostile environment would have similar lifespan. Also don't rule out the wiring for the sensors as with any other electrical device its only going to work as good as its circuit will allow.

From my own experience there were no specific codes being thrown for the o2 sensors. This issue I had ignored for almost a year because the code initially came on during the cooler fall weather and stayed on all winter. In late spring the code went away as the weather warmed up and all summer too which allowed me to pass emissions inspection for registration! Fall came around again this year and the code came back again. The sensors, I am guessing, were providing the vehicle with errant information, probably because of intermittent failure, and after replacing both upstream and downstream sensors from the rear bank, the code went away.

Also no proper running engine should "use" or burn or leak ANY oil and if it does the amount should be so little you wouldn't even think twice about the difference when you wipe down the dipstick. Toyota would say up to a quart of oil every 5k miles was considered normal and acceptable but they were actually just covering up an engineering design flaw.
I've had many vehicles over the last 20 years and in the engines that did have oil loss problems it was never something that was solved by simply switching brands or "weights"

Further more I would like to add my belief that VCM and other cylinder deactivation modes are gimmicks meant to appease the EPA for fuel economy standards and to help buyers to purchase gas guzzling vehicles hoping they will save fuel. Just like the start-stop technology, these fuel saving gimmicks will, over time, cause unneeded stress and wear and tear to the engine and other components. The easiest way to save money with fuel costs is to be mindful about how you drive. Heavy foot = more fuel, light foot = less fuel. I've personally managed to get close to 30mpg on the highway driving my 13 year old Pilot without the assistance of any VCM ( it was not available on the AWD models... hmm, wonder why )
sorry for the long rant !
 

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Discussion Starter · #19 ·
P0420 and P0430 codes are pretty easy to diagnose. Never believe any single item is at fault.
First thing's first... the fuel quality. If you insist on filling up your tank with the cheapest discount gasoline you can find from the oldest gas station in town then I would start filling up from the newest station serving up top-tier fuel. Honda is just one of many auto makers that recommend the use of top-tier fuel in their vehicles for many reasons.
https://www.toptiergas.com/
If you vehicle has been running on fuel of unknown or substandard quality I would highly recommend a quality additive for the at least 2 consecutive tank fill ups. Try seafoam, techron, gumout regane, or redline complete.

Next, check for obvious leaks on the intake and exhaust. Next, check the temperatures directly before and after each pre-cat with an IR gun. There are several youtube videos explaining this process. Temp Readings of both cats should be similar with High temp prior and even higher temp after as the cat is doing its job in burning the rest of the fuel vapor in the exhaust stream. The final cat after the 2-1-merge has no sensor to check its efficiency.
If you temp readings look good then it is time to start looking at maybe replacing the o2 sensors. I would do both at the same time given the age - anything over 100k miles would be suspect. Most iridium plugs last about that long so figuring sensors constantly exposed to the same hostile environment would have similar lifespan. Also don't rule out the wiring for the sensors as with any other electrical device its only going to work as good as its circuit will allow.

From my own experience there were no specific codes being thrown for the o2 sensors. This issue I had ignored for almost a year because the code initially came on during the cooler fall weather and stayed on all winter. In late spring the code went away as the weather warmed up and all summer too which allowed me to pass emissions inspection for registration! Fall came around again this year and the code came back again. The sensors, I am guessing, were providing the vehicle with errant information, probably because of intermittent failure, and after replacing both upstream and downstream sensors from the rear bank, the code went away.

Also no proper running engine should "use" or burn or leak ANY oil and if it does the amount should be so little you wouldn't even think twice about the difference when you wipe down the dipstick. Toyota would say up to a quart of oil every 5k miles was considered normal and acceptable but they were actually just covering up an engineering design flaw.
I've had many vehicles over the last 20 years and in the engines that did have oil loss problems it was never something that was solved by simply switching brands or "weights"

Further more I would like to add my belief that VCM and other cylinder deactivation modes are gimmicks to lure buyers to purchase gas guzzling vehicles hoping they will save fuel. Just like the start-stop technology, these fuel saving gimmicks will, over time, cause unneeded stress and wear and tear to the engine and other components. The easiest way to save money with fuel costs is to be mindful about how you drive. Heavy foot = more fuel, light foot = less fuel. I've personally managed to get close to 30mpg on the highway driving my 13 year old Pilot without the assistance of any VCM ( it was not available on the AWD models... hmm, wonder why )
Thanks for the thorough explanation!! I definitely got a code a couple times after buying gas at a particular gas station, most likely was low quality gas. I stopped going there because it was so obvious. I most likely will add an additive:) So far the check engine light has been much better since I changed the 02 sensors. My laser iridiums have way over 100,000 miles. I am going to change them soon! I've been wanting to get and IR gun for transmission fluid changes on my other cars. They now say the sealed transmission fluid does not need to be changed for the life of the SUV, but I tend to go over 200k on my cars so I am a little suspect of lifetime transmission fluid, I think that may need a thread of it own.
 
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