Scary Diagnostic Light

welcome!
it means the computers have detected a problem. might be minor, might be serious. the only way to know is to read the trouble codes with tech stream diagnostic software

 

That's kind of a personal philosophical choice.
You say generically "acquired", so I'm hoping that means you didn't pay a lot for it. Because the only thing really determinable from you descriptions is that as described above..you have a problem that could be anything from minor to major.

Personally, I'd be worried more than a breadbox, but less than storage locker.

 

Example of minor, you put it into "D"rive with the door open. Example of major, you have no oil in the engine.

Get the DTCs (diagnostic trouble codes) read.

 

Unlike the cars in the movies and TV, the Prius can't speak English or any other language a typical driver can understand. It speaks the Prius dialect of OBDII. Thankfully, there are lots of devices that can translate, so if you plug one into the car's OBDII port the car will gladly tell you what's ailing it.

@bisco mentioned Techstream. That's the ultimate and can be the cheapest tool if you have an old laptop and the knowhow to install it. Easier and quicker is a wireless OBDII adapter and a phone app like Dr Prius, Carista, or Torque Pro. Also pretty inexpensive. The free route is to have a car parts store read it, but their readers usually don't speak Prius.

 

You should be worried exactly enough to:

Take it to a Toyota dealer to diagnose the problem.....should be less than $200 to get an idea of what the problem IS.
OR
Start shopping for a "new" car.

Unless you enjoy inconvenient adventures, just continuing to drive it should NOT be an option because it may not keep running very long.

 

OR
Start shopping for a way to read the codes yourself, which might set you back less than one dealer diagnostic charge the first time (let alone the hassle of masking up and getting your car to the dealer), and will do the same for you for free every later time your car offers trouble codes, for as long as you own it.

Some buddies and I got placed, back in 1984, while extremely tired, in a rental car that said to us loudly, as we pulled out, "ALL MONITORED SYSTEMS ARE FUNCTIONING."

 

I really did laugh out loud at that one. Actually, my Prime "talks" to me with messages on the MID. In fact, it insults me every time I get in the car with a message telling me to put my foot on the brake and press the start button to start the car. Duh!

 

Actually that could be REALLY helpful.......for someone who "borrowed" your key FOB intent on stealing your car but wasn't familiar with how it worked.