check engine light 2002 kia rio rxv?

the check engine light comes on and off every couple of weeks in my 2002 kia rio rxv. The car is running as normal (no leaks,smells,not over heating etc..). The light will come on and stay on for a day or so, then go off and stay off for about a week or two. What could this be? ps...it has regular oil changes, tune ups, it has a new timing belt, gaskets,plugs,water pump and more.

common problem with the 4.2L is o2 sensors, depending on the code. you need a obd11 scan tool and it will tell you which bank is faulty. your vehicle has 3 o2 sensors.