4WD Electronic Control Unit
WARNING: This page is about a different car, the 2002 Toyota Tundra and 2001 Toyota Tundra. However, it is still accessible from the selected car via links, so may be relevant.
4WD electronic control unit monitors all inputs from the position switches, VSS, PNP switch, and the touch select switches to control the transfer shift actuator and the ADD actuator, which controls all the transfer case shifts and gear selections.