2016 qx80 transmission speed sensor

Mechanics are puzzled. Infinity is displaying speed sensor not recognized. Driving the vehicle: the transmission does not shift until vehicle revs above 3000. Mechanic changed outer sensor. The vehicle still displays no sensor recognized. A little background. The vehicle first started displaying 4-wheel drive engaging disengaging. Cleaned the 4 wheel drive knob in console. 4 wheel drive went out. But speed sensor still throws code. Ideas? Do you think the knob is still dirty and perhaps causing the computer not to detect the speed sensor? Thanks in advance