Thank you for your posts, sahmed and dmg. I too have had my 2016 Sonata PHEV shut down without warning, at freeway speed. The dealer near where this occurred worked seriously at restoring the car to its original condition, but the original problem is not really diagnosed. For now, I'm not driving on any freeways. I am also waiting for a planned recall of all Sonata PHEV's, scheduled for May. Hopefully Hyundai Central will figure out how to solve this problem.
I am curious if failure for others occurred under high engine load. My car's failure took place near the end of a 200 mile drive, going uphill at 75 mph. According to my dealer, the car computer's decision to do an instant shutdown was meant to avoid a battery fire. Somehow, the software was unable to maintain gasoline power as backup.
Also, if dmg could offer the contact email/phone for asking Hyundai for a buyback this would be very helpful.