05 Chevy Aveo Chk Eng Light comes on

At first it coded a P0420. Had the Cat replaced but now I get the light but when coded it says no codes stored. Reset the system and after a few days it came back on yet still no code. Any ideas please, I am trying to help my daughter, it's her car and my help is long distance.

If it actually is the check engine lite, there has to be a code. Have it rechecked with the appropriate scanner.

Agreed. Some rudimentary scanners will not display pending codes.