It was purely a software bug (and fixed already): "The problem began when Tesla rolled out an update for a new calibration value for their electronic power ass

It was purely a software bug (and fixed already): "The problem began when Tesla rolled out an update for a new calibration value for their electronic power assist steering system only to have alerts about the update a week later, according to the NHTSA. Tesla has released a firmware update to recalibrate the issue already. According to Tesla, 97% of the recalled vehicles had an update installed that addressed the issue. There have been no official reports of injury linked to the potential loss of steering assistance."