Rep Power: 0

Civic 2010, 189,000 KMs
I had this engine warning checked by a mechanic a few months ago, and I do not remember the actual code, but the description was something similar to the title.
The first time he cleared the error code, and cleaned the top sensor. The light came back after a week or 2, and around 50 KMs.
A month later I visited him, and this time he removed and cleaned the down sensor(only), and this time it glowed in around 15 KMs
Since I did not not have any specific problem because of this engine warning, I left it as it is for last 2 months.
Yesterday I bought the Dura Lube Severe Catalytic & Exhaust Treatment and on tank with more than 1/4th gasoline I drained the whole bottle, and to my surprise, engine light was gone in 2 minutes after starting.
However, the happiness did not stay for long, after 20 KMs, it came back.
After another 5 KMs, I filled 93 octane gasoline about 3/4th the tank thinking that a better grade fuel will assist the process.
A couple of queries which came to me, which I think people who know more about about cars can help me with from what I mentioned( without the error code, and assuming the title is matching with the symptoms)

1. how can i differentiate this issue, whether it is a bad sensor, or a bad catalytic convertor
2. does the time it takes for engine warning light to come back say something ?
3. as to how I handled the catalytic convertor cleaning solution, was it OK, voided its effectiveness, or did I do more damage
4. Is it OK to run with a higher concentration of catalytic cleaning solution in gasoline
5. can this treatment be repeated often, by which is it expected to bring in better results if not achieved in the first try ?

 
Rep Power: 125

P0420 is what you're describing. Sensors don't fix that.

Clearing the code only causes the sensor to reset. It goes through however many drive cycles before coming back on once it rediscovers the data. If you're in an emissions state, cat needs to be replaced.

 
Rep Power: 367

I am sorry, your cat passed away.
it lived for 14-15 years, let him go and consider a new cat
soon, it will start plugging and engine will start losing power. Worst will be it will not even start.
living things need to eat, but that mean it need to push it out.
It will be like if they plugged your exhaust when you have a diarrhea.

 
Rep Power: 0

I also suspected it to be an issue with the catalytic converter. But in that case, why did the engine light turn off after adding the catalytic cleaning solution to gas ? and then after 15 KMs it turned on ? what do you think have happened in between ?

 
Rep Power: 367

if it turns back on in that small distance...
You have a dead animal in your exhaust.

 
Rep Power: 0

animal in exhaust pipe ? or did you mean to say something else in a humorous way ? I did not understand..

 
Rep Power: 367

your cat is dead

 
Rep Power: 222

The cat cleaning stuff can help sometimes. Sometimes the cat is too far gone. Get an o2 sensor spacer or a new cat.

 
Rep Power: 0

@Colin42
Immediately after adding the cleaner, the engine light went off. But after 20 KMs it started to glow again. Any explanation as to why this happened. If the cat was completely gone, then why would the sensor think the system is OK ?
What happened in that 20 KMs is what making me wonder.
I was expecting the worst. But it gave a small hope, and then made me feel more desperate.

 
Rep Power: 222

The cleaner probably helped a little but not enough to get rid of the code permanently. You could try another bottle or two.
Probably just need to replace it though.
Honda's are very picky about cat performance, so if you do replace it dont get a cheap one unless you want it to throw codes in 6 months to a year.

 
Rep Power: 173

My catalytic converter died back in 2018. The engine light would turn on some trips and turn off on others, P0420. I managed to keep it off just long enough for an emissions check (Arizona lol) in 2020 with a sensor spacer. After I pounced on a good deal on a Magnaflow catalytic and installed it (end of 2021), the engine light hasn't been on since. Getting a new one is probably your best option, especially if you have to go through emissions. Crap, that reminds me, I need to go through emissions again...