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Discussion Starter #1 (Edited)
Code P420 / flush gas tank

Hi,

About a year ago I started to get a 401 and 420 codes on my Odyssey 200 LX. Came at the same time. I fixed the 401 by cleaning the EGR path as descrtibed in another thread. Plus used the Techtron fuel cleaner as described. Did reset the codes at that time but the 420 came back after 250 miles. Did try to reset again but it would come back after about 250 miles. Then I tried to not let the fuel tank to go low (not below the half) and the code is gone for more than 600 miles.

Do you guys know what could cause this? I am thinking that this is caused by dirty gas tank. If that is the case how could I get it clean.

Please advice.

Best Regards,
Levon
 

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Discussion Starter #3
Hi William,

Thanks for information. What I am really looking for is why it does not come up when I do not let the gast tank to get to near empty. Th reason being is that if the Cat converter is at fault then it should show the same results regardless how I fill the tank.

Also, how to clean the gas tank if it is dirty.

Thanks,
Levon
 

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Discussion Starter #4
I used a Techtron fuel cleaner couple of times and now the code is gone for 1500 miles.

Looks like it was not a CC issue.

Regards, Levon
 

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The Converter is at a marginal level so any slight change can make it fail or not fail. The reason I posted the article is it explains what can cause it and a lot of things to check. There is no firm answer as to why any small change males it fail or not fail other than a wag. How long did you drive it befor fixing the 401. A failing EGR system will deteriorate the converter over time. A close inspection of the O2 and other sensers with a good OBDII scanned may show some deficiencies.
 

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Discussion Starter #6
What could cause the behavioral difference between full tank vs almost empty one other than a dirty tank. I just want to understand the options before getting the tank drained/cleaned and/or CC replaced.

Regards, Levon
 

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You need to get access to the Honda drive cycle and a good scanner. It is possible that cat converter test has certain pre-conditions and one of them could be the fuel tank level.

So what could happen is that ECM has deferred running the cat converter test. That can be confirmed if you check the I/M monitor status using the said scanner.

On the other hand, if Techron is keeping the CEL off, keep on using it and be happy!

- Vikas
 
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