[Sewie]

Unfortunately, sometimes you have to spoonfeed the techs. I had the same/similar problem with my locker. Button lights up, but locker doesn't engage. When I took it in, I explained that to the Service Manager and the tech and told them they need to open up the diff to diagnose it, not just test the button and look for codes. Sure enough, they found worn/chipped teeth and I got a new rear axle.