E53 trailer hitch install - What does the 15-pin trailer module X609 do??

[VDRZANE]

What does the 15-pin trailer module X609 actually do when I plug it in? Is it telling the X5's computer that I now have a trailer hitch installed and thus changes the transmission gear changing? I hope not!! I am not towing stuff very often and would hate for it to change how my X5 drives! Maybe it only interacts if a brake controller is installed (which I do not have)?

Does anyone know what exactly this X609 module does? Thanks!

[hayaku]

no, it controls the lights on the trailer to match that of the car, sends over the brake signals if you have a brake controller, turns off rear pdc when the plug is in, does send some power to the trailer for charging/etc of the trailer's elec system.. and a few other things i'm sure...