2008 Prius 230,000 just purchased months ago. Just drove down Mount Washington, which pushed my traction battery all the way full, almost never happens. Couple hours later while on the expressway, the Red Triangle, CEL, and red car with exclamation point came up, I think I was in cruise control because it hesitated. Seemed to drive fine after. I stop, check oil, coolants and battery (12v) all are good. This is my first long trip in this car. Mileage has been lower than my work commute trips. 48-53 for work. 41-45 on this trip. I attributed the difference being so much more weight. AutoZone read codes, but their computer showed nothing. 12v Battery tested good. I am 700 miles from home though. I disconnected the battery to reset codes, they all disappeared. No idea what happened.
You'll need to find a Toyota Hybrid aware scanner, not all scanners can read hybrids properly. In the future you can try additional auto shops or just procure you own device. Now you have to wait until the code(s) are thrown again
There is also a yellow ! In a circle with brackets/parenthesis around it. Quick search shows something with brakes.
How did you check coolant when your car was hot? You need to open the radiator cap, not just look at the reservoir level
Not necessarily, you check at the radiator to be sure your system does not have a leak. Under certain conditions the system will leak and the reservoir will be full, even if the radiator is empty. Verifying your coolant level is just making sure that is not your problem. It may well be something else.