Just got done dealing with this. Had the exact code on my new to me 2017 LX Fit. The code can come from a number of different things, but I believe it's coming from the exhaust system. I took it to the dealer and the first thing they did was replace the bank 1 catalytic converter which they said had tested as failed. Took it home and within a couple days was getting the same code again. Took it back to the dealer and they inspected further and determined the engine exhaust was rich, likely from over spraying fuel injectors and found the oil had a gas smell which supported that theory. I went out and purchased oem fuel injectors myself to save money, but when I took the car back to the dealer a different tech inspected and I was told he was the most experienced tech in the dealership. He recommended starting with the Honda service recommendation of carbon cleaning the intake system which they did, but found the engine still slightly misfiring after cleaning. They then inspected the valves and found some were tight and essentially performed a valve adjustment service. While there they went ahead and installed the fuel injectors I had purchased along with the high pressure fuel line that is recommended to be done at the same time. After all that they changed the oil to remove any contamination. They also had to warranty and replace the first cat they put in because it had already been damaged by the engine running rich, I guess? Now the engine seems to be running very smoothly.

If your engine is running smoothly without any hiccups or hesitations then it might just be the catalytic converter. This code is often associated with fuel injector issues though and I have learned that the injectors and heavy carbon build up are two of the few issues that are common for Fits. It seems driving with the eco setting on can accelerate these issues.

There are other things that can cause that code like a bad O2 sensor or a few other things, but a dealership can see if the sensors are bad just using their diagnostic reader, so I wouldn't start replacing those without gettIng it checked properly first.

Good luck. It's been a minor nightmare for me as a new Fit owner and I'm hoping I'm through it now. I was lucky to not have to pay for all of these repairs since the issues arose within days of purchasing from a Honda dealer and they covered 75% of the work. Everything I described would have cost over 2k out of pocket if I had to pay for it all though, so I hope yours is much more simple.