My 2017 75kw MS (late 2017 with refresh) suddenly experiernced a failure of the power steering assist while driving, and had to be towed home. So far, the closest Tesla Dealer has not been helpful, indicating they cannot do anything remotely to diagnose the issue, which I find doubtful, and won't address the issue until the car is brought in for service. I'm over 150km from the closest Tesla dealer and so need to do some trouble-shooting locally in case things can either be fixed here or fixed enough for a road trip down to Tesla.
I figure the problem has got to be either software, electrical, or mechanical in nature. To that end, I've worked on the electrical side of things and checked for bad grounds (none), and bad wire connections (none) on the assist motor unit and torque sensor unit, and inspection has indicated no problems with the insulation integrity of any of the visible wiring. Mechanically, the steering links and steering gear seem to work smoothly when the weight is off the car (manual with no assist), with the steering operating smoothly from far-right to far-left, suggesting that there is no mechanical jams or excess stiffness in the mechanical linkages. This all leads me to point to a software (or firmware), or assist motor control-board, or torgue sensor issue, or a failed assist motor as the culprit, at which point there should be fault indicators in a technical log somewhere. If I had some understanding of Tesla's remote analysis capability (ie over the car's web-connection), procedures etc, I think this would enable me to be more specific about what Tesla can do to help trouble-shoot this issue remotely. There is also the question of whether Tesla's mobile service would be able to provide diagnostic capability physically connecting to the car's OBD connector.
If anyone can provide information on the sort of remote diagnostics Tesla can do that might help shed light on the problem, that would help me a lot. Any thoughts will be welcome.