I was viewing the video this comment [1] mentioned, and found another video which shows what happens to the circuit boards inside the motor when when you submerge a Tesla, like the case in TFA: https://www.youtube.com/watch?v=OOZ_FvfnN6k&t=13m48s

(oh, and the on-board system still boots even after additional high-pressure cleaning: https://www.youtube.com/watch?v=P5_J5h2UFiY)

[1] https://news.ycombinator.com/item?id=17403127