I tried to test the wheel sensors based on a post I found for another model of BMW, but the post said there were two pins in each sensor and we seem to have three. I did check all four corners anyway and they all tested the same, but not what the post indicated. I'm thinking my wheel sensors are OK since I got the same reading on each. I did find that there are also sensors on the bottom of the break fluid reservoir, but they look OK. No idea how to test them. I think I'm going to need to take mine to the dealer because it seems to be either the steering sensor (and the computer needs to be reset when it is replaced) or the control unit.
Others have indicated that you can pull codes to see what the problem is, but I tried to pull codes with two different code readers and both reported no codes. I just have a solid DSC light.