driver side headlight low beam not working?

The headlight control for the system is sent by the BCM which sounds like it has gone bad. There is a chance the ground for the headlight has gone bad. To check the ground you can use a test light connected to the positive side of the battery.

https://www.2carpros.com/articles/how-to-use-a-test-light-circuit-tester

Unplug the bulb and test the black wire, the test light should light up, if so i would replace the BCM, you can get a preprogrammed unit by searching Google or Ebay. Here are the headlight wiring diagrams so you can see how the system works and the location of the BCM and how to change it out. The BCM is in the kick panel on the passenger's side. Check out the images (below). Please let us know what happens.