said by GlenQuagmire:
I call the dealership last year when the OEM cat failed and they told me that it was not covered under warranty. It was covered up to 100,000 and at the time I had 102,000 on the car.
I would call Chevy Customer Care directly to confirm it. My 2001 Pontiac Grand Prix had a clogged cat. converter 2 year ago; a few months later, GM sent me a letter to acknowledge some defect with their cat converters on 2001 (and up) cars and extended the warranty to 10yr/120,000 miles.
Being yours is 2003 car and Impala & Grand Prix are similar cars, GM could have used the same cat. converter.