Weird event this morning. I went out to run an errand so I unplugged the car, got in and backed out of the garage before I noticed my battery level was at zero, my engine was running and the check engine light was on. Last night I had used up the battery so as I got home I did a temporary override of my charge programming to start immediately and plugged in. I don't have an OnStar subscription anymore so I don't know what the codes are. I've got an appointment to take it in Monday morning, but I was just curious to know if anyone else has run into this problem.