Basically, get the car into the dealer. Something ain't right. It could just be a failure of the SES indicator, but there's no way to know without the dealer running a code scan. OR, if you have OnStar, press the OnStar button and they can run remote diagnostics on your car and tell you what the problem is.Service Vehicle Soon Light
This light will come on and a chime will sound if it detects a problem on the vehicle. The Driver Information Center (DIC) may display a message such as Low Coolant, Power Steering, Engine Reduced Power, etc. These messages may help you determine why the service vehicle soon indicator is on. See DIC Warnings and Messages on page 3-48. If this happens, see your GM dealer for necessary repairs to maintain top vehicle performance.