Red Triangle came on while driving - out of the blue

2007 Prius 215,000 miles. Car has been a champ for the almost 2 years I've owned it, buying it with 150K miles. No real troubles and I've been driving it constantly as you can tell. Had an extended warranty repair done back in the winter when dash lights went out completely yet car would still start & run. Replaced 12V battery back them trying to diagnose trouble and it was original battery anyway. Daughter was driving when almost all dash lights came on including the red triangle. She came back home, turned it off. Next start was just red triangle and check engine light with red car on center display. Now it's just the check engine light and red car after sitting for an hour. I plan to take it in to get check engine light checked out but any suggestions?
Thanks

 

I hope it is something this simple. After sitting in the garage for a couple of hours, the problem has disappeared. I haven't driven it far yet so who knows? For the short drive up and down the street to test it, nothing unusual happened. I'll check the fan and battery vent and hope it doesn't come back. The extended warranty work was to replace the module in the dash that controls the display including the mileage indicator. I had to leave it at the dealer while they shipped the part in so that they could certify the original miles. They even put me in a rental car (a 2014 Prius) so I was happy and didn't have to lay out a dime. It was actually based on information I found on this Prius chat forum. I was able to go to the dealer with a service bulletin and they honored it. I pray this isn't the beginning of something more serious but it does have high miles. Fingers crossed. Thanks