Model S 90D with current software. After a 3/4 mile drive to a local grocery store, when I tried to back the car out of its parking space, I was unable to move the steering wheel. Using a great deal of force, and moving very slowly, I was able to move the car to a relatively safe parking space away from other cars. The car seemed to be operating correctly except that the power steering was not working making the car essentially non-driveable. While moving the steering wheel the feel was “notchy” and hard to turn, almost as if the steering was actively trying to prevent the wheel being turned. Not just hard to turn as a failed hydraulic power steering unit would be. I called roadside assistance and while waiting on hold I re-booted the main display by holding down the two knurled knobs on the steering wheel while depressing the brake pedal until the Tesla “T” appeared on the main display. At that time I was able to speak to a service technician who remotely re-booted the instrument panel display and told me that there were no errors visible. The power steering was still inoperative. He asked me to power down the car, which I did, waited about a minute and then depressed the brake pedal to turn it on again. When the car powered on, the power steering was operating normally. I was then able to drive home, albeit slowly in order to be safe should the power steering fail again. Car was towed to service center, checked and driven overnight with no reoccurrence. They are proactively replacing the steering rack and verifying everything is OK. I will update this thread when I get the car back and a full report.