Extremely tight on money right now, p0420 code being thrown on my check engine light from the code reader.

after driving for over an hour, the converter is giving off enough heat to slowly drive my engine temp up when i’m idling in traffic, not to the point yet where it shuts off but certainly close to the red zone.

i guess my question is would anyone have an idea of how long i might have until i HAVE to replace it? when i drive locally (little to no highway speeds and no traffic) it gives me no issue. it’s when i drive an hour into a larger city and an hour back with intermittent traffic that it starts to interfere with engine temp. i’m not even sure if it’s just that it could be cleaned or if it genuinely is about to be done for - i’m not a huge car person unfortunately

sitting on 175k miles if that helps. think it might be original cat