2006 Prius only getting like 12 mpg

Check oil level

 

Is it halfway between the two dimples on the stick? Or halfway between the fullest of full dimple and the bottom of the stick?

When the car detects certain faults, it does go into a limp mode or a problem mode where it can do all sorts of things to limit. However a Prius using "only" the gas engine (can never actually happen, but...) should get low to mid 30 mpgs. If you are getting 12mpgs average you have something else wrong that making the car-go-forwards motion harder than it should be.

 

how many miles on her?

 

Can you hear a fan by the back seat running very fast?

 

If I had a dollar for every time you said that I could buy a new Prius for cash. The good one, not the cheap one.

 

more than, 'check the 12v health'?

 

If I also got a dollar every time you said that I could buy 2 Prius.

 

Certainly you have a check engine light?

If the RTOD was for anything other than low oil pressure, you should have a DTC stored. Maybe you can get a health check performed to see what's lurking in the ECU history?

12mpg should be drastic enough that a problem is right there tapping us on the arm saying "look at me"

Clogged cat?
Stuck injector? Cat glowing red? engine louder due to blowing exhaust donut gasket out?
Is this 12mpg as displayed on the MFD, or as calculated by miles driven and gallons added to fuel tank?