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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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