Why will your steering wheel not return to center after turning?

The most likely cause is a bad steering rack. The valves inside the rack could be stuck, broken or blocked. You could also have a bad strut(s) or ball joints that are binding the steering linkage. It could also be bad or broken motor mounts.

Though less likely, it could be the bearings inside the steering column are binding up, or something pressing against the shaft and keeping it from turning freely. The most likely problem is the steering rack.