my check engine light came on what could it be

hi, I have a 2008 suzuki sx4. When i was driving on the highway, the engine light came on and the cruise control stopped working. I scanned the computer and it was a P0420 code. I cleared the code and the car was fine till i went on the highway again and the same problem and code came back. Any ideas?

Either an o2 sensor problem or the catalytic converter itself has failed, need to determine which.