When it is dark enough outside and the exterior lamp control is in the automatic position, the headlamps come on automatically.

The vehicle has a light sensor on top of the instrument panel. Make sure it is not covered, or the headlamps will be on when they are not needed.
The system may also turn on the headlamps when driving through a parking garage or tunnel.
Lights On with Wipers
If the windshield wipers are activated in daylight with the engine on, and the exterior lamp control is in AUTO, the headlamps, parking lamps, and other exterior lamps come on. The transition time for the lamps coming on varies based on wiper speed. When the wipers are not operating, these lamps turn off.
Move the exterior lamp control to
or
to disable this feature.
Daytime Running Lamps (DRL)
Hazard Warning FlashersRestraints
Specifications
Module Power, Ground, and MIL
Front Impact Sensor, Retractors, and Driver/Passenger Air
Bags
Side Impact Sensors and Side/Roof Air Bags
Air Bag Indicator and Disable Switch (C99)
...
Windshield Washer Pump Seal Replacement
Removal Procedure
Open the hood.
Remove the windshield washer pump. Refer to Windshield Washer Pump
Replacement
Using a small flat-bladed tool, remove the washer pump terminal seal (1)
from the washer solvent container (2).
Installation Procedure
Position the washer pump ...
Reporting Safety Defects to the United States Government
If you believe that your vehicle has a defect which could cause a crash or could
cause injury or death, you should immediately inform the National Highway Traffic
Safety Administration (NHTSA) in addition to notifying General Motors.
If NHTSA receives similar complaints, it may open an investig ...