For BLIS to work while towing the trailer must be less than 8.2 feet wide (per manual). If you told it your trailer was wider, it automatically turns BLIS off while towing. The BLIS sensors can't see around a trailer wider than that.The BLIS never asked me for length of my Trailer, just asked if my trailer was wider than 8 feet. I clicked yes, and that was it. I am not sure it works properly. Can anyone advise me if I am doing that right?