If I were you, I would do what I'm planning to do. I'm going to change over to coil springs in the rear to replace that awful rear self leveling suspension. It will cost $350 in parts, and probably $150 in labor, including having the dealership reprogram the computer to delete self leveling. Rather than spending $100 or so for diagnosis, and who knows how much more to fix it, this may well be the thing to do.

Thanks to MrBMW for bringing this to my attention!