annoying problem I need help

[thermal]

What year civic do you have? Is your cat gutted or stock? You have to understand that a catalyst code does not mean that your cat is bad. It will most likely mean that your O2 sensor is going bad. If you have an OBD2 civic (96 up), your primary O2 sensor calculates what's coming into your cat while the secondary O2 sensor calculates what is happening (or rather what is being processed in the cat based on what the primary O2 sensor initially read before hand. Any erroneous or insufficient calculations will toss a CEL. This CEL can also place your ECU on a limp mode. So, my suggestion is to either borrow or get another secondary O2 sensor to see if the same problem occurs.