MPG dropped

Replace 12v, no need to further troubleshoot.

 

Over what trip distance? The MPG display is tied to either Trip A or Trip B. If the distance is short, it means little. And it is specific to the previous driver's trip conditions and style, which don't match yours.

(*) Your driving conditions are different, so a drop is not meaningful in itself;
(*) Because your conditions are different, you should reset the MPG displays, erase the previous history, and get a direct reading of your own MPG, not a mixed number contaminated by the previous owner's results;
(*) You are new to hybrids, there is a learning curve, so it is not 'your bad', at least yet.

Do you have a separate digital multimeter to verify the voltage? I have not been confident in the absolute accuracy of the readings on my OBDII-port monitor, and have been suspicious of some other readers' internal readings.

This vividly illustrates the MPG penalty of short trips. It takes a bunch of fuel to warm up the engine. On short trips, that warm-up fuel is amortized over just a short distance, causing low trip MPG. The same warm-up fuel amortized over a long trip produces a much better trip MPG.

For a better illustration, reset a Trip meter at startup for a number of days. Then watch how that trip's MPG starts out pathetically low, then increases as the trip gets longer and longer. Non-hybrids do the very same thing, except that on long trips, their MPG is capped to a much lower figure.

For more exploration, you can reset the meter again after the engine is fully warmed, and then get a direct readout of that MPG without having to drive as long a distance to average out the warm-up fuel penalty.

If your typical commutes or trips are short, e.g. under ten miles, then you are stuck with disappointing MPGs. But remember that non-hybrids are even more disappointing on the same trips

 

You said they tested the battery? What was the voltage reading of the battery, "out of car"?
With the car in "ready" mode, running, only 11.9??? It should be 14 volts, or more. If you are not
getting that, then you have a problem with the hybrid system not putting out enough voltage to the battery.
Or the "new" battery has a problem and pulling a lot of power.

As Grit said, have amazon send you a replacement battery.

 

battery's fine, clean the egr

 

If the 12volt battery is reading less than 12 volts, it is not fine.
If he's only getting 11.9 volts at the battery while the hybrid battery is active, with the car in ready mode,
the battery MAY be good, but there is a problem with the hybrid system that supplies the 14 volts to
charge the battery and run the other 12 systems, like the computers......

 

I'm glad replacing the battery helped!
When your driving, or the car is "ready", you are getting 13.9volts, correct?
I'm wondering if you have a draw somewhere, that's why the battery voltage drops.
Maybe inverter coolant pump? Engine water pump? I would get that checked out, to be safe.
You should also carry a jumper, incase it drains the battery down, at least you'll be able to jump it
to get you going.

 

Don't forget that your MPG will drop when it gets cold. If you are not hypermiling, your last readings (45 MPG) look normal for winter driving... ...depending on location, of course.

 

But you say you are getting 13.9v, so that is good.
What I meant was... MAYBE the engine coolant pump or inverter coolant pump are running
after the motor is turned off.
Or some other device is still drawing power from the battery.
It just seems odd that a NEW battery would drop below 12 volts after having 13.9 volts going to it
for a period of time. Maybe a dome light on, in the trunk???

 

I had this happen to a normal car of mine. I thought it was the battery and replaced it. It was fine for a while, then died on me again when it sat for a few days, undriven (this is not normal).
Long story short: The alternator was dying and only intermittently working. This had been going on for months. Easy to test, replaced and problem solved. I know the Prius is different in this regard.

Perhaps a bad relay is causing parasitic drain when sitting while off?

 

Decrease in MPG becomes noticeable at temperatures below 50 degrees F - but again, that depends on how you drive and how far you drive. It's more noticeable when you hypermile and MUCH more noticeable if you drive/commute short distances (less than 5 miles to destination).

I live in Norfolk Va, which, on the east coast, is about as close as you can get, weather-wise, to Seattle. Although it doesn't rain as much here, during the winter, when there is precipitation, it usually gets a few degrees above freezing and rains.

Generally I see a decrease between 5 and 10 mpg during the winter. But then again, I usually commute only between 2 to 5 miles, on any given day, just to go to the gym and do errands, and only rarely do I use the interstate. When you do this, the ICE is operating at low efficiency for a large percentage of the trip. Also, I hypermile obsessively, which makes the lower efficiency much more noticeable (for short trips only).

During trips to Seattle (before I retired) I rarely went anywhere without getting on the interstate. Lower mpg is much less noticeable for trips greater than 5 miles since the vehicle is operating at higher efficiency during most of the trip.

 

So "hypermile" is when you use up more gas than normal?

 

No. Hypermiling causes the "apparent" drop in mpg to become more noticeable because you are using LESS gas during periods when the ICE has already warmed up (hypermiling does not improve mpg as much when the ICE is still warming up). E.g. If I get only 50 mpg for a 2 mile trip without hypermiling during the winter, I will typically get about 55 mpg during the summer because the car warms up quicker (a difference of 5 mpg). WITH hypermiling. I typically get around 60 to 65 mpg (sometimes 70 mpg) for the same trip during the summer, but I still only get 50 to 55 mpg during the winter (a difference of roughly 10 mpg). Hence, hypermiling increases the "apparent" loss of fuel efficiency from summer to winter by about 5 mpg.