[Jwitz]

I wish I knew for my own purposes, but I have some off the top of my head sugesstions. You could turn on acc (not engine running) and have someone hit the 4wd button and find out if any noise is coming from your add unit. If not I would probably pull the connector and attach a light to the connector (this would be good if you had the toyota wiring diagram). If the connector has no positive signal, then maybe a fuse or relay has gone. if it's okay, then its certainly possible that the add unit has gone. I would say if the dealership wants more than 1500 to replace it, you would do better to buy the manual hub kit and rig the add to lock (which I have no idea how to do...) sorry to be so vauge, but I really have no idea, simply suggusting what I would do in your situation...