Very well could be the BCM.
The low beam relay is controlled by the BCM
Check the low beam relay
Another possibility could be the Headlamp dimmer switch which is part of the multifunction switch..
I would think more on the lines of the relay or the BCM.
Remember ,if it is the BCM,The BCM needs to be programmed to the vehicle when installed.
An advanced scan tool is required for this..not a Diy'er job...install is,not programming.
Vehicle wont run without BCM being programmed.