I thought I read that since it was an average that you had to drive for some time (days, months?) to get it back on track. So let me know if you think it will eventually correct, or if I should maybe pull the 12v power again to reset it. So if I fill up with gas it resets to 0.0, but goes directly to 41.x-something. Then I can watch it go from 41.5, down to 41.2, or if I try to maximize mpg it ticks up only a little to 41.6. Before the new OEM 12v battery I was getting a much broader normal range, and could get up above 50 mpg if I tried or below 40 if I gassed it.
You are splitting hairs, 41 to 50 MPG is statistically insignificant. Just ignore it for 3 or 4 tanks.
Are we talking about instantaneous mpg or tank average mpg? You need to reset the consumption monitor after every tank or even every trip... that will give you a more accurate reading. After every fill up... the miles counter resets to 0... but the average MPG monitor to the left of that does not. Hit the reset button an see what kind of consumption you're getting. Since you just disconnected the 12v battery... you are likely suffering from the WEAK EV State which results in WEAK EV output at city speeds (0-42 mph) and can reduce city mpgs by 10+. This may be what your trying to describe as the cause of your low mpg... you just don't have a deep enough understanding of your Prius to verbalize it correctly. You can read more about this in my WEAK EV State LOW MPG mechanism post here.
if you care about mpg's, best practice is to always do manual tank calculations, and ignore the guess o meter
So my 2008 will reset both the mileage and the average at a fill up (I am not talking about the instantaneous reading under the "power flow" graphic). My point about it defaulting to 41.x is not that my mpg is "less" or impacted in anyway, nothing has changed on the car except preemptively changing the 12V battery which was still working fine, the point is that it is not accurate and is displaying gibberish and doesn't change more than a few tenths no matter how I drive. I will test the actual milegae with the odometer and report back what I get, but to be clear I am not experiencing "low mpg" per se, the MFC average mpg is just acting strangely and not updating with accurate info. Your linked post is interesting, seems relevant, I am not sure about your description of a high/low HV battery, but I can tell when the engine is accelerating on ICE only and the display shows 2 bars on the HV battery and it typically happens at a stop/light when AC is on and using power. The ICE doesn't seem to really charge the HV much, but the regen brakes do make the bars move up. Once it has semi-full bars it dirves normally with EV+ICE acceleration and I can have AC on without "losing" bars on the HV battery. I am regretting replacing the battery without using a 12V source top preseve settings. Do I pull power agian and try to get it to re-calibrate?
As an owner of a 2009 Gen 2... the average mpg does not reset at a fill up. Only the miles traveled does. The average Mpg will still be calculating from however many miles since you hit the reset. So if you fill up with gas and the average mpg says 41.5 and miles says 234... the 234 miles will be reset to 0... but the 41.5 average mpg will stay and continue calculating average mpg based off the last reset push... not the 0 miles... whether its the 234 miles just from the previous tank or 5,000 miles from the last reset button push... you have to hit the reset button to reset average mpgs. Average will then be calculated from the moment you hit reset until you hit the reset button again. Posted via the PriusChat mobile app.
Just to reiterate what TheLastMojojomo said, you might want to take a closer look at that screen on your next fill-up. The 2004-2005 did work the way you describe auto-resetting to zero both the average MPG and distance traveled. This behavior changed with the mid-cycle refresh for the 2006-2009. With this change the auto-reset only reset the distance traveled to zero but left the average MPG as it was.
Thank you both, I will look again, but I know I see 0.0 on the screen after a fillup. If my memory is correct it wouldn't creep up from 1, 2, 3, it does go back to something higher like 36mpg. Then I would see the mpg range fluctuate normally, I could hypermile and it would get up above 40, then get on freeway and get above 50. But now it just sticks at 41.x no matter how I drive, like it still fluctuates but in a much smaller range in the decimals. I will report back on next fill up.
Just to update after a few tanks of gas, I did notice that the MPG stayed stuck in the 41.x only fluctuating by a few tenths. I checked actual mileage from gallons used vs odometer and I was closer to 50 MPG average. Then recently the display broke out of 41 MPG on a long freeway drive and I was in 42, then 43, and now 44.2 MPG, so it seems like the average displayed MPG is slowly building up again, even though I get higher MPG real world. This started when I pulled the 12V battery and wiped out the stored average, and before I was consistently getting above 50 on the display after all of my tuning and hypermiling. So I guess I will just leave it and see if it eventually builds up and matches the real world MPG of closer to 50. Also I can confirm that I was wrong and the MPG doesn't clear after fill up, only the odometer.
What you should do is hit the reset button after every fill up to reset average gas mileage. This will give you a much more accurate calculation of mpg per tank... instead of a running average that you can't keep track of due to the mileage traveled being reset but not the average mpg being displayed. Reseting the average mpg calculation after every fill up will show you a better relationship to real world mpg rather than waiting to for the running average to level out and not being able to measure miles traveled accurately.
I have to say I'm shocked that so many people post gas mileage without ever checking. The proper way is full up the tank, drive and when you fill up again, take the miles and divide by gallons put in. I have two cars and both say not the same as doing it the right way.