What would mechanics look at?

12 volt battery: 12.1 volts. That's a big issue. 12.6 or above after sitting overnight.
Did you get it from Toyota? Check the warranty on it no matter who you got it from.
You could try charging it at 5 amps or less for about 8 hours to bring it to a full charge.
Since you 90% city driving and short trips, the 12v battery doesn't get a full charge.
After charging, wait about 30 minutes for the battery to cool off and stablize, then check the voltage.
If it's the Toyota OEM battery, it's only through half it's life at 4 years.

You could adjust the tire pressurs to 36 or 38psi, for all four.

You should figure out why the "mode" buttons are not working. Drive in "ECO" mode will
give you the best MPG.

69 is fairly cool, even in Florida. I keep mine at 75, 95% of the time. And on recirculate, on auto.
Usually I will have it set lower when I first get in the car if it's been siting in the sun. But I open the
windows(about 1/2 way), fan on medium high, recirc is off. Outside air at 90 cools quicker than the 125 inside the car.
Usually in less that a minute I will close the drivers window, then the passenger front window.
Then I hit recirculate. And fairly quickly I close the rear windows. I turn the temp up to 74 and put the a/c on "auto".
When I feel comfortable, I put it to 75. And go back and forth from 75-76.
90% of my driving is highway. But even in the city I pretty much do the same thing.

All these things add up.
The most important one is the 12v battery. 12.1 volts is extremely low for a Prius.
That would be the first thing to address. All kind of weird things are likely to happen with a
weak and/or bad 12volt battery. And they are easy to change.


How old is your 12v battery? What is the voltage reading of your 12v battery after sitting over night? 3/2020 70,000 miles. 12 volt battery is reading at 12.1 volts.

- How much of it is city vs. highway? Roughly what's the average speed in overall and and of each segment? Is there a lot of stop and go driving? 90% short trips, 10% highway. Short trips have stop and go. Average speed probably 40 mph.

- What are your tire pressures? Front 35, rear 33.

- What modes are you using, if any? "normal", EV, power, eco? I don't know because the buttons are not working

- HVAC settings? Are you using the heater, AC, auto mode, etc.? If using auto, what temp is it set to? Use the AC mostly, auto set at 69.

 

Other than dragging brakes, a Prius that loses significant mpg with no change in driving habits is very likely close to the end of its hybrid battery capacity. Less ability to store energy means less ability to assist the engine for better mpg.

I have seen it many times.

 

make sure the air filter housing top is on correctly, check the oil level and tyres pressure

 

Michelin X-tour 195/65R 91

Found it! Incorrect tire size.

 

Could bear on it, but if I read this right the tires were changed quite some time ago but the MPG loss is much more recent.

Can you get back to expected MPG by temporarily disabling AC?

When a Prius air conditioner loses some of its refrigerant, the automation in the system will force the compressor to work much harder to get the same amount of cooling. This shows up as reduced MPG for a while, and eventually the compressor works itself to death.

If you can "magically" reclaim your expected mpg by running without AC, it may be worth having that system checked out by a pro.

 

Yeah 12.1 volt reading on the 12 volt battery doesn’t bode good. Depending on how you measured. Optimum would be first thing in morning, car off, using a digital volt meter. If practical pop the hood the night before, to avoid any “waking up” of the car’s electronic systems. Not imperative though.

sounds like you’re in good hands with Tampa Hybrids, with EGR cleaning and all.

 

I think @Grit's making fun of your typo, he lives for that. Should read "195/65R15". The "91" is kinda secondary, a speed rating?

The 195/65R15 means:

195: tread width of tire in mm
65: ratio of width to height of tire in percent (height will be 65% of 195, or ~127 mm)
R: that it's a radial tire (pretty much universal nowadays)
15: the nominal diameter of the tire in inches; rims for it will also be 15"

 

I was thinking of 91” tires were installed.

 

Hi Jo - My two cents is to ask Todd if he can find why your drive mode buttons are not switching modes. Since that is the only thing on your list that stands out.

I'm a big believer in the DrPrius app coupled with an inexpensive ODB2 bluetooth adapter for the main purpose in Fl. being able to keep an eye on your hybrid high voltage battery temperatures. Ask Todd what he thinks of a setup like that. DrPrius is free to install on a cell phone. If you want to be able to control the hybrid battery fan speed from the app, the developer of the app asks for a $12 subscription fee.