Blind spot monitoring mirrors

My 2016 Tacoma with Blind Spot monitoring mirrors will beep and light up when a vehicle is next to my vehicle towards the rear on either side. After the first week of ownership it work fine, now only the blind spot lights indicators lights up when a vehicle is on my blind sides. It light and beeps for rear cross walk and traffic. The blind spot monitoring button is on at all times. The manual does not mention about this function, The truck 4600 miles. Toyota tech and i drove the truck and confirm it should beep when the light comes on on either blind side. Is en't that is the function of a blind spot warning system is all about , Especially when i pay a shit load of Money for a Glorified Rice Runner Tin can that the seat do not have any up or down adjustment and Garbage for navigation system. Maybe some day Toyota will get it Right!.