Intermittent Master warning triangle with Hybrid system warning light

You might want to try getting the little 12V battery load tested. I see the battery it isn't very old, but a vehicle driven a handful of miles is a recipe for troubles. A load test at a local parts shop will sort that out. They usually don't charge for the service. Alternately, there could also be problems with electrical connections to ground. These intermittent warning lights sure get your attention, and are usually the first sign of a depleted 12V auxiliary battery. A seasonal change in the weather also seems to trigger these things.

 

Anyone in that situation, with any car really, needs to find a way to keep the 12 V battery charged.
That usually means connecting it to a battery tender when not driven........or at least once a week overnight.

If that isn't practical, you might need a new battery every 3 years or so.
Keeping a "jump pack" with you would be a good idea too.

 

Well as long as the MGC is running good you should be an okay shape these funny little Japanese cars don't like sitting.

 

If practical, drive the car (much) more, or use a "smart" (AGM compatible) charger to maintain the 12V battery.

Your OBD scanner is very likely not capable of communicating with most of the 15-16 ecu's on a Gen2 Prius. Here is a thread reviewing several scantool apps and devices.
https://priuschat.com/index.php?posts/3290690

Posted via the PriusChat mobile app.