This happened to my 2007 CTS within one week of buying it three weed ago. Lucky for me the dealership fixed it but it was in their garage all week. They replaced the ECM then had trouble registering my keys with it. It's been almost two weeks and the problem hasn't came back. I say lucky for me but I don't know if they would have fixed it if I hadn't bought their service plan. So I feel like I'm paying for it anyway.