Prius Mpg Anomaly

[Colin Burney]

I have a February 2007 Prius TSpirit with about 13k miles. It's an ex-demo which had around 10k on it when I bought it in Feb 2008, so you can see it hasn't done a lot of miles whilst I have had it.

Up until a week ago it hadn't been used for about 3 weeks (holidays etc.) and had just been sitting on the drive.

Came to use it last Monday and the remote fob would not unlock the car, so I used the driver's door key to gain entry, but which does not enable the opening of any other doors or the tailgate. I put the ignition fob in the dash slot - nothing - not a flicker. Obviously a flat Battery. I used our other car, a Yaris Verso, to jump-start the Prius using the special terminal under the Prius bonnet. Then I gave the Prius a run down the motorway, following which I put the 12v Battery (in the boot) on charge for around 10 hours. So far,so good and it has run fine since then.

But here is the anomaly: before this flat Battery incident, the on-board computer had indicated that the average mpg was 48.3. It has never indicated more than this and I really have no idea as to its accuracy, but it did seem reasonable.

However, in the five days since the battery was re-charged, the average mpg has risen to 59.1 according to the computer - this over a distance of about 70 miles involving a number of short journeys.

This seems strange and I wondered if anyone could offer any explanation.

[RedStork]

Might sound like a silly question, but have you ever reset the MPG counter? If it's been a demo car over 10K miles then it wouldn't have been driven as well as a full time owner. Just sounds to me as though the MPG readout has never been reset and the flat Battery caused it to reset and now you're seeing a true reflection of the MPG you're getting out of the car.

[Chris Ray]

Had you ever reset the computer, using the reset button on the info screen?

If not, I suspect that the average before was for the life of the car, and now the Battery going flat has reset the info, so that the new mpg figure is the average of the last 70 miles only

I have covered 52000 miles in my gen 2 over 16 months, with all types of trips, and my average mpg ( according to the computer) is 56.9

Hope this helps

[Colin Burney]

Thanks to Red Stork and Chris Ray.

What you say make sense, and no I have never done a reset. I feel a bit like Homer Simpson. DOH!

[Chris Ray]

No probs Colin, there is a lot to learn on the Prius MFD!!

[G7PCQ]

Hi

Correct me if I am wrong but does the MPG computer reading not reset itself when you fill up?? My one does.

[Chris Ray]

Only the tripmeter resets, not the average MPG, unless you press the reset on the screen

[Trafficman]

On my 55 reg Tspirit both reset when you refuel.

[timberwolf]

On my 55 reg Tspirit both reset when you refuel.

It was changed for the 2006-2009 model. B) I can't see the logic that it still automatically resets the miles on a fill-up but not the average MPG - I would have thought that the reset button should have been made to reset both miles and average MPG?

[G7PCQ]

My Prius is a 57 and both reset after filling up.

[timberwolf]

Interesting, I had understood this to be a change that occurred when the model was refreshed in 2006. My 2008/2009 does not reset the MPG automatically. When did it change for the UK model?

[Mkuk0]

nope nor does my 58 model, only the 'mileage on this tank' resets automatically, there is a reset button on the bottom eight hand side of the screen to reset the average MPG.

[tone_uk]

nope nor does my 58 model, only the 'mileage on this tank' resets automatically, there is a reset button on the bottom eight hand side of the screen to reset the average MPG.

My 56 only reset the miles on tank and not the overall MPG

[fuel miser]

nope nor does my 58 model, only the 'mileage on this tank' resets automatically, there is a reset button on the bottom eight hand side of the screen to reset the average MPG.

My 56 only reset the miles on tank and not the overall MPG

Ditto my 06 T4.

[Sagitar]

My Prius is a 57 and both reset after filling up.

How can you ever know what the overall average is if it resets at each tank fill?

If they both reset then they must both show the same reading (i.e. the average since the last fill) and one of the readings is redundant.

Or am I misunderstanding what you are trying to say?

[timberwolf]

My Prius is a 57 and both reset after filling up.

How can you ever know what the overall average is if it resets at each tank fill?

If they both reset then they must both show the same reading (i.e. the average since the last fill) and one of the readings is redundant.

Or am I misunderstanding what you are trying to say?

On the Gen 2, on the MFD (multi function display) there is only a single average mpg gauge and next to the mpg gauge is the miles travelled (note the trip meters and odometer are separate and displayed on the main combination meter). On the later model gen 2, the mpg can be reset by the owner, or the value can be lost if the Aux 12v fails or has to be disconnected for maintenance.

With only the one mpg gauge, I find it useful to reset the gauge on each fill-up, so that I can tell more quickly how changes to my driving style or the weather may be affecting my mpg.

As to your original question, people work out their mpg by recording values such as the miles travelled and litres of fuel to fill-up the petrol tank. If you search the internet, you'll find sites where people record their mpg for anyone to view!

[Sagitar]

My Prius is a 57 and both reset after filling up.

How can you ever know what the overall average is if it resets at each tank fill?

If they both reset then they must both show the same reading (i.e. the average since the last fill) and one of the readings is redundant.

Or am I misunderstanding what you are trying to say?

On the Gen 2, on the MFD (multi function display) there is only a single average mpg gauge and next to the mpg gauge is the miles travelled (note the trip meters and odometer are separate and displayed on the main combination meter). On the later model gen 2, the mpg can be reset by the owner, or the value can be lost if the Aux 12v fails or has to be disconnected for maintenance.

With only the one mpg gauge, I find it useful to reset the gauge on each fill-up, so that I can tell more quickly how changes to my driving style or the weather may be affecting my mpg.

As to your original question, people work out their mpg by recording values such as the miles travelled and litres of fuel to fill-up the petrol tank. If you search the internet, you'll find sites where people record their mpg for anyone to view!

Thanks. My remarks were prompted by the post that said:

"nope nor does my 58 model, only the 'mileage on this tank' resets automatically, there is a reset button on the bottom eight hand side of the screen to reset the average MPG". - and what followed

Until today, I have been driving a Lexus that shows the m.p.g. for the current fill and the m.p.g for the lifef the vehicle (or until deliberately reset).

It sounds like I added two and two and made five.

I guess I should leave it untill I have a better understanding . . . . . . :bookworm: