Hey all, I just experienced this phenomenon on my 2003 K1200LT motorcycle.
My gas mileage took a significant hit when my O2 sensor went bad! Evidently the computer forces the fuel mixture to rich to avoid damaging the engine. An additional indication is that the tail pipe was very black and sooty (is that a word?). Has anyone experienced this issue on their Fit?

 

Yes, it's a problem with all vehicles, I have not experienced it with my Fit but did with my MR2.

 

Yes, a bad O2 sensor can affect mileage. Your description is correct. The PCM runs a rich mixture in the absence of a signal that is within the prescribed limits.

 

I have a cat delete on my honda fit and my check engine light is on, but i really havent noticed a drastic change in mileage. i mean ye when i abuse it i notice my car runs harder and ye i burn alottttt of gas but if i run it nice n easy i think it stays the same. what can i do to avoid the check engine light? an O2 sensor spacer or whatever you call it?