1999 Trans Am low voltage

[Painter369]

Hey guys. I have a 1999 trans am. When I start the vehicle I have around 9-10 volts and the car starts and cranks just fine. Pop right off. But the check gauges light comes on and the voltage will stay around the 10 mark for around 10 minutes while driving around and then all of a sudden it?ll jump up to 14-15 volts and stay there while I drive. Alternator starting to go?

[Mecinoid]

Sounds to me like some sort of drain on battery. Load test battery first. How long to you let you car sit? Overnight or weeks on end. Sound like it could be the alternator but, start with bad battery then go to alternator. Car does really funny things with low battery. I would suspect that first. Should have at least 12.5 volts prior to start up. 10 volts is right on the edge to start motor. I think battery going bad. How old is battery? Over three years is suspect as well.

I expect you figured this out since this is a 6 month old post. Tell us what you found please. It will help others.