I came across on this problem a year ago. Read in the forum. Very confusing information, mostly without solution. Bought a scanning tool, reading live date, reading values. It was time consuming and also confusing. I also did a research for which lacquer thinner to use per Scotty Kilmer (a showman). Went to the dealership. They gave the result, which AutoZone gave me for free – replace the catalytic convertor. I talked to the technician and he said, it is due to drivers’ habits. – Bullshit! I went next day to talk to his supervisor. I brought with me the service manual to show them they didn’t make a drive test to read properly the live data. He said, we knew about this problem years ago. There is a technical bulletin, showing it is ECM at idle and low revolutions was wrongly programmed by HONDA. Interesting. There was no recall. First thing I did is to update the ECM. The second is coming, to buy a new cat. Please advise from your personal experience which brand is better than Honda?

Attached is the technical bulletin.

 

crazy idea.... ever consider an o2 sensor spacer?







I had the same CEL on my 1st gen honda insight, and this little spacer saved the day. oem cat's are wayyy too expensive, about 1/2 the cost of the car.

 

If you can update the ECM, I would clear the code and see if it comes back. Might save you the purchase of a cat?

 

No , the update itself doesn't resolved the problem, because I assume cat is contaminated. I did it at the dealership for $80, but light is still on.

I guess it might help if is some misreading from the oxygen sensor.
Where to mount this O2 sensor spacer? Upstream or downstream? How to choose the proper spacer?

 

Spacer would go in the downstream hole. Spacer is trial and error really. Pick a size, put it in and clear the code. If it returns try a smaller one.

 

I read a bit about this spacer. It will solve the problem with state inspection, but not the issue with engine work. The cat replacement only is not an option also.
Definitely, the update didn't resolve the bad performance.