We've asked Tesla for comment. It previously said that it delivered the May update out of an "abundance of caution" and that its EVs were "10 times less likely" to catch fire than gas-powered cars. Its statement at the time made clear that the software would affect charge and thermal management settings.

The update had been prompted by a Model S bursting into flames in Hong Kong, although there have been multiple seemingly spontaneous fires over the past several years. Much as with the lithium-ion batteries in your mobile devices, there's a chance that overheating or charging issues could trigger chemical reactions that set the EVs' batteries ablaze.

There's no certainty that the NHTSA's review will lead to a formal investigation or recall request. Nonetheless, the case illustrates the virtues and vices of over-the-air software updates for cars. They can mitigate or eliminate problems that previously would have required a dealership visit, if one was even possible -- how many cars can receive brake performance tweaks through a patch? At the same time, there is a concern that car companies might use software to avoid dealing with deep-seated hardware issues.