I recently purchased a 2010 CTS 3.6 luxury with 68,000 miles on it. They told me that they needed to replace the 02 sensors also. It just seemed strange to me that after the Check Engine Light being on for many many days it suddenly goes off. Since I have had it the car runs much much better I think cheap gas and it sat for a while didn't help the car I do have a heavy foot use to drive a 2005 mustang gt. This 6 cylinder is getting better performance the more I drive it. I do think I will take it out this weekend and do some driving and blow it out.