Hi Debbie928. Welcome to the forum. It sounds like the generator is quitting intermittently. There is no way to sugar-coat it. GM went from the world's second best generator to the worst pile ever built. It is not uncommon to go through four of them in the life of the vehicle. Due to their design, they have a tendency to develop voltage spikes that interfere with the many computers on the vehicle. They are a big source of running problems even when they still are keeping the battery charged. An easy way to verify if it is the cause of computer problems is to start with a fully charged battery, then run the engine with the small plug on the side of the generator disconnected. You should easily be able to drive this way for 20 - 30 minutes before the battery runs down.
Since the warning light is turning on, you know it's time for a new generator because everything is self-contained in the unit itself. Unlike other systems where you only buy and replace what is defective, you replace the entire system on GMs. The advantage is there isn't much to troubleshooting and diagnosing the problem.
One big thing that is becoming more widely known now is that to prevent repeat failures of the new generator, the battery should be replaced at the same time. If the old battery is working fine, use it in a different car built before 1987. They have the older design generator that doesn't cause so much trouble. As batteries age, their "internal resistance" goes up. Basically that means their ability to absorb the voltage spikes goes down. People seem to have relatively little trouble when replacing the battery and generator together.
Saturday, June 12th, 2010 AT 2:31 PM