2001 Prism check engine light

The air filter was not snapped properly in place causing the Oxygen Sensor to go out. I had the problem fixed. Now about every third oil (every 3,000 miles because I have 125,000 on the car) change the check engine light comes on about two days after and stays on for 3 days. It doesn't matter how many miles I drive. I took it to Auto Zone while the light was on and it told me it was code 420 Catalytic Converter or some engine oil leak. Has anyone else had this problem? I'm getting great mileage with no other problems. Just this goofy check engine light.

[quote=geema]The air filter was not snapped properly in place causing the Oxygen Sensor to go out. I had the problem fixed. Now about every third oil (every 3,000 miles because I have 125,000 on the car) change the check engine light comes on about two days after and stays on for 3 days. It doesn't matter how many miles I drive. I took it to Auto Zone while the light was on and it told me it was code 420 Catalytic Converter or some engine oil leak. Has anyone else had this problem? I'm getting great mileage with no other problems. Just this goofy check engine light.