The headlamps are controlled by the Body Control Module (BCM). The BCM sends power to the low beam relay and supplies ground for the high beam relay. The main fuse for the low beams is labeled HDM in the under hood fuse box, there is also an HDM relay. Check the fuse and the relay - if no problems are found you will need to check the BCM for fault codes using a scan tool. Don't forget to check the bulbs - they could both be burned out!