There are many possiblities, and a scan with a GM Tech II scan tool would be the easiest way to find the bad part, other than that REQUIRED starting point, you will spend many hours, and mabe a few unneeded parts will be replaced along the way without the scan. I can send some reading about it so you can see that even with a scantool, there are many tests to perform, in your case I will say it sounds like an intermittent problem and could be a ground wire problem. There are sensors in each door lock, and the trunk lid, any of those could also cause this. What does the security light on your dash do when you enter the car? Insert key and turn it to on? Start car? Does the light EVER come on with the car running?
Tuesday, December 29th, 2009 AT 3:51 PM