Engine light

Welcome to 2CarPros. Do you know the code numbers for the EVAP and catalytic converter? A bad O2 sensor could have caused a problem that would damage a converter so if the code is something like a P0420 or P0430 I wouldn't be surprised to see them. As for the code clearing itself, EVAP codes only clear under specific conditions related to the exact code, or if they are cleared with a scan tool. The converter code however should clear IF there is no actual fault in the system as it runs as a constantly monitored system. I would start by pulling the current codes and posting them here, then we have a starting point.

Was afraid that was one. That is the code describing a bad or inactive catalytic converter. To verify that code you would look at the O2 sensors data in front of and behind the converter. If the rear O2 is not reading correctly then it could show that code, but that is very seldom the problem. Usually the only way to remove that code is to replace the converter in question.