Originally Posted by cpaharley2008
For some reason I'm thinking the anti-sway does not activate the brakes in a conventional manner in that the brake lights are not activated and neither are the trailer brakes, but instead one or more wheel brakes are activated to stop wheel spin which can lead to the vehicle swaying. One time I can around a curve and I lost traction, the dash lite up with symbols and the car came out of the spin straight.
Yes, this is how modern stability control works, except that brakes are not just applied to stop wheel spin, they are applied to apply rotational torque in the needed direction (for instance, apply right-side brake to keep vehicle from spinning to the left) and they can choose between front and rear wheel for best effect (e.g. use front brake if oversteering, rear brake if understeering).
In the descriptions that I have seen the "trailer sway control" is just an adjustment of the behaviour of the programming of this now-standard vehicle feature. It is activated by an indication that a trailer is attached, which can be provided by the integrated trailer brake controller - all modern brake controllers test the connection to the trailer so they "know" whether or not one is connected. It's not a big deal to include in the tug, but it would certainly be beneficial for towing.
There are aftermarket systems from AL-KO (for Euro-style mechanical trailer brakes) and from Dexter Axle (Dexter Sway Control
for North American style electric trailer brakes) which sit on the trailer and detect sway, then apply the trailer brakes when sway is detected. I didn't know if any of the systems in tow vehicles do this, until the article linked above. Also, the Dexter system applies the trailer brakes on only the desired side, which is fundamentally more effectively, and impossible for anything in the tow vehicle to do (because there is only a single brake control circuit from tug to trailer).