Had this happen to me today. While driving to drop the kids off, occasionally the steering wheel would for a brief moment get very stiff, then go back to normal. AP2 AutoSteer never became available, despite being available on the same roads the previous day. When I got to school, driving over the curb and over the bump of the security gate rail apparently caused all power steering to just fail, and the wheel stayed stiff and the car flashed a "Car Needs Service - Steering Assist Reduced" sign on the dash and on the touchscreen. I was pointing straight at a handicapped spot so I just drove right into it and parked, dropped off the kids and went back to call Roadside Service. ETA was an hour for someone to come take the car. Before they called me back I was fiddling with various resets and leaving the car/coming back, pressing the brake, and the steering came back. I decided to take the car myself straight to the service center. When the steering assist is off, it's WAY more stiff than an old school manual steering car. You will need both hands to turn the wheel. Luckily it briefly triggered off only one more time before getting on the highway, and I got to the service center safely. There they wanted to test drive it, and the technician could feel the issue happen occasionally. He was able to trigger it again completely by going over a few speed bumps. AP2 AutoSteer never became available again either. The initial diagnosis is a loose wire somewhere that's causing the power steering to fail. A few people have had this issue with their Model S's as well, looking around the forums. The service center is going to take a pretty careful look, as its a serious safety issue. I'm pretty disappointed that this is a thing. If it's a loose wire, there's some shoddy assembly line work happening, or some pretty poor quality control. I'm just glad nothing scary happened, as it could have.