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Discussion Starter · #1 ·
Honda Pilot 2009 with 217xxx miles on it. Both P0420 and P0430 codes got shown yesterday. Researched a lot and figured I should buy OBD2 scanner with live data to see the output of downstream O2 sensors. Bank 1 sensor had a perfect flat line around 700-ish mV (don't know why P0420 showed up).
Bank 2 sensor fluctuated a bit (200 to 800 mV), not a lot like the ones I saw on many YouTube vidoes but definitely wasn't flat. The readings were taken when the car had been on for at least an hour. The temps of both CATs were around 980F.

The car feels fine. I revved it to the red zone and it didn't stall or felt like missing throttle. The idling seems fine. I don't think the car loses any power when driving. The exhaust pipes seems normal. There is no smog or thin white smog which is fine. If the CEL hadn't been on, there would be no difference in my driving experience. I have yet to see if there is a difference in the fuel economy in the long run.

The Pilot has been in Tennessee for the past 8 years or so.

I am thinking to erase the codes using the scanner to see if they show up again. Can anyone please advise how can I fix it? Should I keep driving and see what happens? Can I damage something if I keep driving like this? Any other diagnostics I should do? Any other live data I should look at? Thanks a lot!
 

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Nobili spiritus embiggens pequeño sparus tyre.
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Is Tennessee a state that requires an emissions test? Sometime those codes point to a just slightly under threshold catalytic converter.
 

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I always pass along my basic maintenance list to try and get on top of a problem before it causes engine damage. # 1 is disable the VCM. I use S-VCM. This will keep your engine running on all 6 cylinders 100% of the time. My list...
  1. Disable the VCM
  2. Air filter New/Clean
  3. Intake hose secured. No leaks
  4. Clean MAF. Remove. With CRC Electronic Cleaner or MAF Cleaner, spray a few short bursts directly into the visible electrodes (no soaking). Let dry of condensation before re-installing.
  5. Spark plugs New/Clean
  6. Spark plug tubes oil free. If oil is present replace valve cover gaskets grommets and spark plug tube seals. Will also need a intake manifold gasket set to do this.
  7. Coils firing. Oil free. Replace oil soaked boots if found.
  8. No O2 sensor specific codes. Replace.
  9. Replace PCV valve
  10. Replace EGR valve
  11. Use full synthetic oil 0w20. No extended performance or blends
  12. Use top tier 87 octane fuel or use injector cleaner regularly
  13. Italian tune up. Take in some long highway speed drives.
That's my punch list. It's got me to 267k on my Crosstour and still going. I had the Emission codes you have. Hopefully the catalytic converters are not to far gone before these changes.
 
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Discussion Starter · #4 ·
Is Tennessee a state that requires an emissions test? Sometime those codes point to a just slightly under threshold catalytic converter.
My county does not require emissions testing so I’m good there. Just worried if I might cause some bigger engine damage in the long run.
The punch list by Nail seems good. Will try that 👍
 

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Discussion Starter · #5 ·
My county does not require emissions testing so I’m good there. Just worried if I might cause some bigger engine damage in the long run.
The punch list by Nail seems good. Will try that 👍
Should I try erasing the codes and see if they pop up again? Will that create any problems?
 

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Another thing to look out for on your particular year model is the possibility of oil dripping down from the vtec assembly just above the dipstick, into the alternator. If you have dirty oily residue there, you may want to replace gaskets before this causes a costly repair.
 

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Should I try erasing the codes and see if they pop up again? Will that create any problems?
Erasing the codes does not hurt anything. Just know what you are erasing.
 
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My county does not require emissions testing so I’m good there. Just worried if I might cause some bigger engine damage in the long run.
The punch list by Nail seems good. Will try that 👍
You may know this but for anyone new reading this, these Honda engines are quite sensitive to aftermarket spark plugs. We have had many examples on this forum of ones who used Bosch or Autolite spark plugs and started having misfires 👎. I believe some have used Denso Iridium Long Life plugs successfully. Others have accidentally been sold the lower quality NGK IX. The IX may work, but they will not last as long. I recommend NGK Laser Iridiums or NGK Ruthenium HX for maximum durability.
 

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Discussion Starter · #9 ·
You may know this but for anyone new reading this, these Honda engines are quite sensitive to aftermarket spark plugs. We have had many examples on this forum of ones who used Bosch or Autolite spark plugs and started having misfires 👎. I believe some have used Denso Iridium Long Life plugs successfully. Others have accidentally been sold the lower quality NGK IX. The IX may work, but they will not last as long. I recommend NGK Laser Iridiums or NGK Ruthenium HX for maximum durability.
So I cleared the codes this morning and the CEL came back on this afternoon for p0430 only. There are no codes for O2 sensors or any other thing, just p0430 which makes sense as I had fluctuations in the downstream O2 reading for bank 2. This must mean the O2 sensors are working fine right? And something is up with bank 2 CAT.
So I’ve decided to first do all the regular tune ups like spark plugs, MAF, Air filter and reset the codes again to see if that makes a difference. Just wanna rule out all other possibilities before I go down the expensive repairs for CAT itself. Is that a good strategy? Even if that doesn’t make a difference, the car still needs tune ups so that can’t hurt I imagine.
Is it recommended to replace both CATs at once or should I replace only the bad one?
How much longer can I continue to drive like this? 6 months? A year maybe?
How do I tell if my CAT is slightly bad or is it worse? I mean the p0430 will be the same for a slightly bad CAT and a completely destroyed CAT right?
Thanks a lot!
 

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So I cleared the codes this morning and the CEL came back on this afternoon for p0430 only. There are no codes for O2 sensors or any other thing, just p0430 which makes sense as I had fluctuations in the downstream O2 reading for bank 2. This must mean the O2 sensors are working fine right? And something is up with bank 2 CAT.
So I’ve decided to first do all the regular tune ups like spark plugs, MAF, Air filter and reset the codes again to see if that makes a difference. Just wanna rule out all other possibilities before I go down the expensive repairs for CAT itself. Is that a good strategy? Even if that doesn’t make a difference, the car still needs tune ups so that can’t hurt I imagine.
Is it recommended to replace both CATs at once or should I replace only the bad one?
How much longer can I continue to drive like this? 6 months? A year maybe?
How do I tell if my CAT is slightly bad or is it worse? I mean the p0430 will be the same for a slightly bad CAT and a completely destroyed CAT right?
Thanks a lot!
Unless you have to make inspection, P0420/P0430 codes are a product of. I'd leave the old cats, in hopes their efficiency will improve with the changes you make.
 
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Discussion Starter · #11 ·
Unless you have to make inspection, P0420/P0430 codes are a product of. I'd leave the old cats, in hopes their efficiency will improve with the changes you make.
After doing these tune ups, how many miles of driving and days of driving should I wait to see any improvement? If there is any improvement, the CEL should go off right or are there other signs of improvement coz right now, the car runs fine tbh
 

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After doing these tune ups, how many miles of driving and days of driving should I wait to see any improvement? If there is any improvement, the CEL should go off right or are there other signs of improvement coz right now, the car runs fine tbh
I guess it was 5 to 10k when the P0420/P0430 codes disappeared and never returned. We drive mostly highway miles at high speeds.
 
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My county does not require emissions testing so I’m good there.
How do I tell if my CAT is slightly bad or is it worse? I mean the p0430 will be the same for a slightly bad CAT and a completely destroyed CAT right?
I'd leave the old cats, in hopes their efficiency will improve with the changes you make.
I guess it was 5 to 10k when the P0420/P0430 codes disappeared and never returned. We drive mostly highway miles at high speeds.
Daughter bought a PIlot with a P420. PPI mechanic said meh. I cleared it, and even with the reduced driving this past year, it hasn't come back. Put in some highway miles and perhaps a few Italian tune-up.

Catalytic convertors are grossly overpriced. If you feel guilty, buy some carbon offset credits.
 

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All bets are off without disabling the VCM. the cats will continue to clog with burned oil deposits.
 

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How do I tell if my CAT is slightly bad or is it worse?
I learned a number of years ago you can get an indication of cat health by monitoring the output of the AFTER cat 02 sensors with a scan tool or scope. Under idle and steady cruising the graph trace should lazily bobble between about .5 and .8 volts. If it starts to make wider voltage swings and more than a once a second, the cat is getting weak (poor 02 storage). If it swings a wide voltage range 4 or 5 times a seconds, or closely follows the A/F sensor movement, then the PCM will likely flag it. Maybe the Honda techs can tell us the code setting criteria.

I'm with Greasy that disabling VCM and driving it aggressively seems to help clean up cats that are right on the cusp and set efficiency codes occasionally. If it sets the code 10 min after clearing it, the cat is probably unrecovereable, and either replacement or one of the "o2 sensor helper" devices might keep the efficiency codes away.
 

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I have ordered the S-VCM. Should be arriving in a couple of days.
Are FelPro Gaskets good for EGR valve or should I get OEM?
Yes, felpro EGR gasket is ok.
 
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Just noticed a rib crack in the air intake hose. Autozone and advanced have the Dorman OE in stock. Are they good?
Yes, better than having a crack.
148883
 
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