Why would my Buick shut off when stopped at a light and not turn back over.

Hello, Dave here, contributing to RepairPal and providing expert advice since 2010. Many times, the auto stop feature works to shut the engine down -- but if the engine battery voltage is not up to par, it will not start the vehicle back up. I would check the battery for state of charge and the ability to sustain a load. I think you'll find it's not up to the task of starting the vehicle as needed. Other than that, continued testing of the starting system is needed. But I have a hunch that the battery will solve your concern. https://repairpal.com/auto-repair-near-me Click the link or call us at 877-913-1554. We'll gladly find you a certified RepairPal shop in your area.