engine service light

Go by a autozone an have them check it for free might just be a sensor.

The service engine soon light indicates the engine computer has detected a fault. Being the engine is running OK my first suggestion would be to make sure the seal on the gas cap looks OK and the cap is securely installed. If that all checks out OK you should get your 2001 Buick Century into a qualified technician so that the fault codes stored in the computer and be read and properly diagnosed. For more information on your Service Engine Light and what it means please refer to the repairpal encyclopedia. Look under "Check Engine Light".