Consumption Screen MPG not Resetting

I have had a 2005 Prius for one year. I liked it so much that 2 1/2 weeks ago I took delivery on another, now 2006, Prius.

So you could say I like them.

I also have a year's experience (~13,000 miles at an average in-the-tank 50.4 MPG) driving them.

However, so far I am less than enthused with the MPG on the new car.

It probably is too soon to tell, but here are my observations:

1. It appears that something went wrong with the MPG calculation for the first tank. When I picked up the car (six miles on the odometer) the MPG reading was 11!. I should have reset it, but I did not. The calculated MPG slowly went up to 48.1 by the time I filled up at 350 miles. I have concluded that the dealer left the car on to operate the AC (It was a very hot afternoon here in SC, that day) while they did the pre-delivery cleanup. If they used only 0.3 gallons while not moving, that would have explained the behavior.

2. When I actually put gas in the car the first time, using my normal slow fill technique, I only got 4.7 gallons in it for an unbelievable 74 MPG. I speculate that the dealer tried to force gas into the (bladder) tank to make the customer think he was getting very high mileage.

3. I have just refilled the second time, and the average of the first two tanks was about 58 MPG. I am sure that will come down some more. (The second tank MPG on the MFD was a more reasonable 51.7 with me using my best driving techniques, although there were a lot of short trips in there as well as one longer one.)

4. Although it is very diffilcult to tell after only two tanks, it appears that the MPG may be not as good. However, with all of the above, it is really hard to tell.

The main reason for this post however, is that for both fillups, while the tank miles automatically reset to zero after refueling, the MPG did not!!! Of course, both times I reset it manually. I have never had to do this with the 2005 and the 2006 manual says that the 2006 should reset both the MPG as well as the total miles when more than 2.4 g are put in the tank.

I will be discussing the above with the dealer. Has anyone else had this problem?

Thanks in advance.

Bob

 

Thanks to all who responded. At least, there does not seem to be something wrong with the car.

However, it is in direct contradiction to the manual. On about page 150 (about, I am not looking at te manual), it clearly says that the accumulated MPG is reset whenever 10 L (~2.6 gal) is added to the tank. Perhaps the manual, which read the same for the 2005, was just not updated.

On the other hand, perhaps there is a software error.

As you said, perhaps the engineers wanted to be able to monitor the long term MPG.

However, it only monitors it from the time you press the reset button. This does not seem like a very good way to do it but perhaps it is the correct explanation. If you would like to see the results from my 2005 Prius, you can go to www.moxproject.info/prius. (I am in the process of updating the site to add the 2006 also).

So for now, the jury is still out as to whether the new car gets as good a mileage as the old one. There just does not seem to be any way to tell at this time.

I think I have the explanation to the poor MFD reading of MPG. However, I was quite surpised in the very high actual first tank MPG. Perhaps the pump just cut off too soon.

Anyway, I was surprised again when the 2nd tank, actual MPG was relatively low. (Probably due to the pump cutoff too soon.)

Overall for the first two tanks, it's extremely good. However, I just think that it is not accurate.

I have long thought that the variation in pump cutoff sensitivity must surely introduce errors. That is, good mileage for one tank is followed by poor mileage the next. You can see that behavior in the 2005 data.

Of course, the long term behavior is what one wants. However, I am trying to determine as early as possible if the new (2006) car is OK and hopefully as good MPG as the old (2005) one.

Again, thanks for all the replies.

Bob