Sub Zero Temps Warning Lights

I joined this site as I'd searched it for information when our 2014 Prius C (39K miles) was disabled by the recent sub-zero (F) temps.

We got warning lights for brakes (red), regenerative braking, traction control, ABS and the blinking yellow triangle. We are just a year in to the car which we bought used with a completely clean history.

In any event, I don't have a question really, just a report on the outcome: We stop using the car hoping a warm day would sort it out. We put it into our one space garage. No joy. It would start OK and you could move it; but in forward motion the yellow triangle would flash and beep. We had it towed to a dealership -- a defensive move as we didn't want to make things worse! I figured they'd tell me the battery had failed, the ECU was bad, or some other significant repair. They scanned it for codes and found an old speed sensor code but nothing related to brakes or any of the other stuff. They scanned it after it had been inside their building for a bit. They also drove it for 10 miles and recorded performance and searched for codes etc. NOTHING. I was charged some some labor for diagnostic time but that's all and rec'd no suggestions on how to avoid the situation. So I hope it stays above zero!

I wanted to see if others had had a similar experience in the recent deep cold days but also to wonder if I had just waited for the next 'much warmer' day it'd have resolved itself.