fuel economy

You are saying 47 MPG down to 31 MPG.
Winter we see lower MPG, but more like 41 could be expected.

250 Miles / (20 liter x 1000 / 3785 ccs/gal) = 47.3 miles/gal

 

I get the same numbers.

That's quite a drop. How many miles on the odometer? Check tires? Brakes?

 

Well we do not know your driving habits. If its winter and you are doing all really short trips, then 31 is possible. 47 MPG is more normal.

What I like to do, after warm up period. Go on highway for little while say 55 miles/hr you should see some 50 MPG periods on the display. When I see that, then I think it is OK. These days my Prius is doing short local trips so we are starting to see some 35 MPG tanks in winter,

 

Apart from a 50% drop in fuel economy?

 

A set of 4 non low rolling tires could account for maybe 10% drop. A brake problem, brakes dragging, could make a difference. Feel the wheels after a drive, see if any feel hot.

Something is definitely odd, such a drop. No warning lights?

 

Dealer just did fuel mileage check here is how they do it
1.go to gas station fuel car til it clicks off
2. Drive 60 miles
3. Go back to same station same pump pointed in same direction refuel car
4. Divide gals used by miles driven

My used 1.128 gals in 60 miles

 

please do the math for me. 59 mpg?

 

That's pretty good but assumes very accurate pumps which we mostly seem to have here. I do something like that sometimes I get 1.5-gal in a gaso can, and I checked and it was very accurate.

 

Well, low MPG is a symptom.
It can be caused by numerous factors, so you try many of the before mentioned avenues and suggestions. The "easy" obvious things, like tire pressure, oil level, etc, etc...
BUT...

"

I'm guessing that's your biggest hint thus far as to what might be wrong.
The ABS light being on for 15 minutes was trying to tell you something.

If you can afford it? I'd take it to a dealership with the exclamation that you've seen a significant drop in MPG, coupled with the appearance of your ABS light, and let them take a look.
Because that light shouldn't be on, unless there is a problem. Even if it's off now? That's my best shot at direction to go in as far as diagnosis.

Good Luck.

PS.

As well as ABS means BRAKES...which you want to make sure are SAFE and working properly.

 

could be a brake pad dragging or a bad bearing, yes, that could drop the mileage severely.
also check your 12 volt battery health.

 

Who knows? Possibly.
It's a starting point for discovery.

If there is "something" happening with your brakes and/or suspension it certainly could be affecting your MPG.

And IMO, it doesn't really matter. IF your brakes have a problem, as indicated by the appearance of the light, you want to get that resolved anyway. It's a safety issue.

I'd try the obvious things already suggested, and have the brakes checked. The ABS light should not of been on for 15 minutes.

 

1.128 gals for 60 miles is almost 53.2mpg.