Check Engine Light on 04 CTS

Hey guys, I am new to the board and have been having problems with my car and just wondering if anybody had any advice. The check engine light on my 04 CTS has just gone off for the 4th time in the last 7 months. The first time i took it in i was told the sensors on bank 2 (i think) had to be replaced, the 2nd time the cat converter had to be replaced, the 3rd time the sensors on bank 1 (i think) had to be replaced, and I just took it in again today to see what the problem is. I was just wondering if any of you guys know what the problem is and what i need to do to stop this from happening over and over again. I really know nothing about cars, so any help would be greatly appreciated. Thanks.