WARNING: This page is about a different car, the 2013 Acura MDX, 2012 Acura MDX, 2011 Acura MDX, and 2010 Acura MDX. However, it is still accessible from the selected car via links, so may be relevant.
The BSI control unit obtains information from external sensors and switches that are connected to their respective control units.
Fig 1: Identifying Blind Spot Information Control Unit System Diagram