BSM and towing a trailer

I'm trying to set up trailer towing and I'll be damned if I can get the BSM to work "as advertised" when towing a trailer. I've set up the trailer (entered name, length, number of axles, brake type), the Tundra sees the trailer is connected but the BSM lights up right when a vehicle is at the non-trailer spot off the rear bumper.

Is that normal or is there something I'm missing?

 

look for the Thread noted below a page or so back - likely you will find your answer in the replies posted.

Backing with trailer(s) & BRAKE!!! Any way to turn off??

 

What do you mean as advertised? Are you saying the light stays on when a vehicle is right next you and not slightly behind?

 

As I understand the manual, the BSM light will come on farther behind the truck than usual when towing a trailer.

 

Thanks but there was nothing in there regarding the BSM and sensing further to the rear when towing a trailer.

 

https://www.toyota.com/owners/resou...8.html#ch04se050408__ch04se050408050406030701

From the online manual:

The Blind Spot Monitor detection areas

The areas that vehicles can be detected in are outlined below.
When not towing a trailer The range of each detection area is: Approximately 1.6 ft. (0.5 m) to 11.5 ft. (3.5 m) from either side of the vehicle *1 Approximately 3.3 ft. (1 m) forward of the rear bumper Approximately 9.8 ft. (3 m) from the rear bumper Approximately 9.8 ft. (3 m) to 197 ft. (60 m) from the rear bumper *2


When towing a trailer
The range of each detection area is: Approximately 1.6 ft. (0.5 m) to 11.5 ft. (3.5 m) from either side of the vehicle *1 Approximately 3.3 ft. (1 m) forward of the rear bumper Trailer overall length *3 Approximately 9.8 ft. (3 m) from the rear end of trailer *3 *1 The area between the side of the vehicle and 1.6 ft. (0.5 m) from the side of the vehicle cannot be detected. *2 The outer mirror indicator warning may be delayed. The delay increases in proportion to the speed differential with vehicles approaching in the adjacent lane. *3 The system does not support trailers wider than 8.5 ft. (2.59 m) and/or longer than 39 ft. (12.0 m). For box trailers and certain other trailer types that are up to 8.5 ft. (2.59 m) wide and/or 39 ft. (12.0 m) long, the indicator warning in the outer mirror may be delayed if the vehicle in the adjacent lane overtakes your vehicle at a high-speed differential.