I have been dealing with this intermittent issue for 3 years.

1. The classic issue where the cell of the cat cuts the original o2 sensor in half. Replaced with used OEM cat and Denso 234-4353 sensor. Solved issue.
   
2. Drove over something in road and damaged o2 sensor, replaced with another and all was well.
   
3. The 2nd sensor failed soon after install (30 days) and got a replacement.
   
4. The 3rd sensor worked for almost 1 year then starting becoming intermittent. Replaced it August 2020
   
5. The 4th sensor new as of August 2020 is now doing the same thing. It will intermittently throw a P0420. The light could stay on as little as a few days or as long as a month or so. The only pattern I have seen is this can happen when the weather goes from 80f to 40f or so.
   

Any thoughts on this?

STOCK 07 AP2

Question:
1. How do you determine if the cat is good / bad?
2. What is the sensor named in the ODB software? / voltage range should I be looking for?

 

P0420 does not indicate a bad o2 sensor, it indicates the opposite (it is working)

You need a new cat, or a right angle spacer for your o2 sensor (you have a few good o2 sensors sitting around)

 

Thanks for the help, going with a magnaflow oem style.

 

This will probably also set a CEL.

Why not just buy an O2 spacer for your current cat. They're about $5..

 

I apologize for my ignorance. Can you send a link to this spacer?

Why would a brand new cat still show a CEL? Should I have bought an OEM one?

 

Your used cat is also not working up to its potential. 06-09 are very sensitive.

Get a RIGHT ANGLE o2 spacer and point it towards the front of the car. That’s it.

 

If a good, used OEM cat is showing below efficiency...an aftermarket one is going to be below efficiency as well.

If the aftermarket part was of a higher caliber than the factory part...it would cost MORE than the factory part, right?

Your effective options are to:
-Buy a brand new Genuine Honda cataly$$$$t

OR
-use a defouler/O2 spacer on your current cat. If this doesn't work (sometimes it doesn't), then you'll need to find a new Honda genuine catalyst anyway. For $5 to $20...this is worth a shot


Here is one possible option of O2 spacer. A million other items exist.

https://www.ebay.com/itm/Check-Engine-O2-Sensor-Spacer-Light-Adapter-CEL-Eliminator-W-Catalytic-Converter-/224157308425?_trksid=p2349624.m46890.l49292

 

My 07 had some crap aftermarket cat and I replaced with an AP1 cat since I couldn't find an 06+ and I still have the code from time to time, going to hazard a guess that you're used cat wasnt from an 06+ car. I'm 99% sure the 06+ cars had a more strict cat since the system is more sensitive. Like mentioned above just space it out, its on my list as well.

 

The cat doesn't make the cat more sensitive, the software in the ecu does.

 

Thanks for all of that input, I see your points now. I think the used cat was 06+, but I agree if software is picky and its worn. This seems logical.

I did get the 90 degree adapter.

I also got this.
https://www.summitracing.com/parts/MPE-49261

https://www.magnaflow.com/products/4...er?aces=480344

The OEM /federal grade.

Has anyone tried this? I realize its not the super expensive honda OEM. It's also not the china/ebay junk. I feel like the 90 degree is just a bandaid and the cat will get worse overtime and I will be buying one.