P0420 and 0430 error codes on 1997 Mercury Cougar

The car seems to run fine, good power mileage, but need to pass Ohio echeck in july. When I clear the codes they reappear in 1-3 days

2 answers 1 comment
Clearing the diagnostic trouble codes does not necessarily means you solved the problems, learn more about these codes here; http://repairpal.com/obd-ii-code-p0420 and http://repairpal.com/obd-ii-code-p0430
how do i get the engine light to turn off
With the same tool used to retrieve the codes and diagnose the problem. It is very likely that the engine light will go off again if the issue is not repaired.