1. Attachments are working again! Check out this thread for more details and to report any other bugs.

How is "distance to empty" calculated?

Discussion in 'Gen 3 Prius Technical Discussion' started by epboyd, Jan 29, 2010.

  1. epboyd

    epboyd New Member

    Joined:
    Nov 17, 2009
    7
    1
    0
    Location:
    Ottawa
    Vehicle:
    2010 Prius
    Model:
    V
    Hi all,

    Does anyone have any input on how the "miles to empty" reading on the dashboard is calculated? Specifically, how the battery affects this calculation?

    If the Prius were a non-hybrid, obviously it would solely be a calculated distance based off current fuel tank quantity, and an average fuel consumption and speed over a range of time (easy enough), but how would one factor in the battery?
     
    #1 epboyd, Jan 29, 2010
  2. Tideland Prius

    Tideland Prius Moderator of the North
    Staff Member

    Joined:
    Oct 2, 2004
    45,024
    16,242
    41
    Location:
    Canada
    Vehicle:
    Other Non-Hybrid
    Model:
    N/A
    It's based on your previous tank and it's the distance to your low fuel light (you have about a 10 litre reserve after the light comes on).

    It's calculated the same way as a regular car. The battery is not taken into account (if you're thinking about the extra 1-2km of battery power if the car runs out of fuel).
     
    #2 Tideland Prius, Jan 29, 2010
    1 person likes this.
  3. Tom183

    Tom183 New Member

    Joined:
    Dec 29, 2009
    652
    65
    0
    Location:
    Maine
    Vehicle:
    2010 Prius
    Model:
    III
    That may be true at the very start of a new tank, but after that I think it is recalculated in real-time based on your calculated MPG since the last fill-up.

    In other words, if you got 60MPG on your last tank, miles-to-empty might start around 600, but once your current tank is half-gone and you're only getting 40MPG, the miles-to-empty would be closer to 200 (rather than 300).

    Regarding the battery, it is not exactly included or excluded - the calcs appear to be based on your overall mpg since the last fill-up (which includes whatever improvement the battery has been providing, but not any specific # of miles you might be able to get from EV mode).
     
    #3 Tom183, Jan 29, 2010
    2 people like this.
  4. Tideland Prius

    Tideland Prius Moderator of the North
    Staff Member

    Joined:
    Oct 2, 2004
    45,024
    16,242
    41
    Location:
    Canada
    Vehicle:
    Other Non-Hybrid
    Model:
    N/A
    Yup, I agree
     
    #4 Tideland Prius, Jan 29, 2010
  5. Vancouver

    Vancouver New Member

    Joined:
    Nov 6, 2009
    42
    4
    0
    Location:
    Vancouver
    Vehicle:
    2010 Prius
    Model:
    N/A
    The one odd data point I can contribute here is that I was driving down to the States and wanted to fill up across the border, but was running really low, so I added 6 litres in Canada before driving to the States. The km to empty number did not reset at all! It just stayed the same. Does it require filling up the tank completely to go up? I imagine there is some threshold where it just doesn't recognize it should increase the number slightly? The fuel gauge did add an additional bar, so it knew it had more gas. Odd!
     
    #5 Vancouver, Feb 1, 2010
  6. Tom183

    Tom183 New Member

    Joined:
    Dec 29, 2009
    652
    65
    0
    Location:
    Maine
    Vehicle:
    2010 Prius
    Model:
    III
    Good question - did you reset either tripmeters when you added fuel? I have been doing that every time I fill up (and I always fill to full, not partway), so I don't know exactly how miles-to-empty is tripped/reset...

    Two tests to do:
    1) partial fill-up with tripmeter reset.
    2) full fill-up with no tripmeter reset.
     
    #6 Tom183, Feb 1, 2010
  7. Vancouver

    Vancouver New Member

    Joined:
    Nov 6, 2009
    42
    4
    0
    Location:
    Vancouver
    Vehicle:
    2010 Prius
    Model:
    N/A
    I did reset it. It still didn't trigger. Very odd! I watched carefully and it also didn't go down much during the drive to the States. (As if it was slowly figuring out that it had more than it thought originally!) When I filled the tank in the States it instantly jumped to the full normal range, even before resetting the trip measure.

    I'm a bit baffled and imagine there must be a minimum fill required to activate a recalculation, otherwise it just uses a smoothing formula.
     
    #7 Vancouver, Feb 1, 2010
  8. Tom183

    Tom183 New Member

    Joined:
    Dec 29, 2009
    652
    65
    0
    Location:
    Maine
    Vehicle:
    2010 Prius
    Model:
    III
    I think you're right about that - must have to fill up to make it reset.
     
    #8 Tom183, Feb 1, 2010
  9. Tideland Prius

    Tideland Prius Moderator of the North
    Staff Member

    Joined:
    Oct 2, 2004
    45,024
    16,242
    41
    Location:
    Canada
    Vehicle:
    Other Non-Hybrid
    Model:
    N/A
    It's in the manual. You need to add 10 litres (~ 2 gal) min. before the gauge will move.
     
    #9 Tideland Prius, Feb 2, 2010
  10. Vancouver

    Vancouver New Member

    Joined:
    Nov 6, 2009
    42
    4
    0
    Location:
    Vancouver
    Vehicle:
    2010 Prius
    Model:
    N/A
    That would explain it! Thank you, Tideland!
     
    #10 Vancouver, Feb 2, 2010
  11. Tideland Prius

    Tideland Prius Moderator of the North
    Staff Member

    Joined:
    Oct 2, 2004
    45,024
    16,242
    41
    Location:
    Canada
    Vehicle:
    Other Non-Hybrid
    Model:
    N/A
    And in case anyone comes in to read this in the future, it applies to all generations of the Prius.
     
    #11 Tideland Prius, Feb 2, 2010
(You must log in or sign up to post here.)