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

Poor Fuel Economy After Brake Change

Discussion in 'Gen 3 Prius Fuel Economy' started by Tim Jenkins, Jul 15, 2021.

  1. Tim Jenkins

    Tim Jenkins New Member

    Joined:
    Jul 15, 2021
    25
    6
    0
    Location:
    Dalton, Georgia
    Vehicle:
    2010 Prius
    Model:
    V
    FYI, on my screen the 1st video doesn't load, but if you click on the 'pop-out' icon in the upper right hand corner, it plays.
     
  2. TheLastMojojomo

    TheLastMojojomo Active Member

    Joined:
    Sep 14, 2016
    210
    131
    0
    Location:
    US
    Vehicle:
    2009 Prius
    Model:
    Touring
    Your Prius appears to be functioning completely normally.

    It is doing exactly what it's supposed to be doing without cruise control on.

    The low grade regen that is occuring when your coasting in drive with your foot off the brake and gas is supposed to happen.

    As I said before, this is partially to simulate what happens in a vehicle with a conventional transmission.

    Next time you drive a car with a conventional automatic transmission, take your foot off the gas and coast like you did in the video.

    Then switch to neutral.

    You will notice a similar effect of the car coasting better in neutral.

    This is because the transmission doesn't have to work against the compression of the engine to gain speed as it becomes disengaged.

    In the Prius a slight amount of regen brake is applied to simulate that effect and simultaneously deliver a charge to the HV Battery. When you switch to neutral, regen brake is disengaged.

    If you want to continue coasting down the hill at speed, apply your foot very lightly to the gas.

    In the Gen 2 Prius we call this gliding. I don't think the Gen 3's officially have a "glide" mode where the energy monitor shows both zero regen and energy expenditure.

    But if you lightly press the gas it will simulate it as close as possible.

    Others can chime in and verify that I'm correct on all this.

    Posted via the PriusChat mobile app.
     
    jerrymildred likes this.
  3. Tim Jenkins

    Tim Jenkins New Member

    Joined:
    Jul 15, 2021
    25
    6
    0
    Location:
    Dalton, Georgia
    Vehicle:
    2010 Prius
    Model:
    V
    Thank you
     
    TheLastMojojomo likes this.
  4. Grit

    Grit Senior Member

    Joined:
    Aug 22, 2017
    6,103
    4,032
    1
    Location:
    Wilkes Land
    Vehicle:
    2012 Prius
    Model:
    Four
    Now back to the original issue below:

     
    TheLastMojojomo likes this.
  5. bisco

    bisco cookie crumbler

    Joined:
    May 11, 2005
    107,571
    48,862
    0
    Location:
    boston
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    aren't we done?
     
  6. Tim Jenkins

    Tim Jenkins New Member

    Joined:
    Jul 15, 2021
    25
    6
    0
    Location:
    Dalton, Georgia
    Vehicle:
    2010 Prius
    Model:
    V
    I am satisfied to know that my Prius is functioning properly
     
    Raytheeagle and bisco like this.
  7. bisco

    bisco cookie crumbler

    Joined:
    May 11, 2005
    107,571
    48,862
    0
    Location:
    boston
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    i'd say we had the answer last week
     
  8. bisco

    bisco cookie crumbler

    Joined:
    May 11, 2005
    107,571
    48,862
    0
    Location:
    boston
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    and the answer to grits question
     
  9. TheLastMojojomo

    TheLastMojojomo Active Member

    Joined:
    Sep 14, 2016
    210
    131
    0
    Location:
    US
    Vehicle:
    2009 Prius
    Model:
    Touring
    If your Prius continues to get low mpg despite being satisfied that your Prius is otherwise functioning normally, I have discovered a low mpg mechanism that nobody knows about.

    I'm still working on all the specifics and will hopefully post all the evidence in a single post in the next couple weeks.

    Here is a link to a comment on Reddit I made that describes this mechanism.

    If the mechanic who did the brake job disconnected the battery, this could be the cause of your initial low mpgs and immediate transition to power mode.

    It sounds like the mechanism I've discovered but not described in detail.

    Maybe find out if the mechanic disconnected the 12v battery during the brake job as this might explain your symptoms more.

    Posted via the PriusChat mobile app.
     
  10. bisco

    bisco cookie crumbler

    Joined:
    May 11, 2005
    107,571
    48,862
    0
    Location:
    boston
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    you mean like this?
     
  11. Tim Jenkins

    Tim Jenkins New Member

    Joined:
    Jul 15, 2021
    25
    6
    0
    Location:
    Dalton, Georgia
    Vehicle:
    2010 Prius
    Model:
    V
    I will ask, but assuming he did not disconnect the battery, how do I fix or reset this mechanism?
     
  12. bisco

    bisco cookie crumbler

    Joined:
    May 11, 2005
    107,571
    48,862
    0
    Location:
    boston
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    there's nothing to fix or reset, you're already back to your old mpg's
     
  13. TheLastMojojomo

    TheLastMojojomo Active Member

    Joined:
    Sep 14, 2016
    210
    131
    0
    Location:
    US
    Vehicle:
    2009 Prius
    Model:
    Touring
    If he did not disconnect the battery, then this low mpg mechanism will likely not apply, and is likely not the cause of your low mpg.

    But when you said "My Prius transitions quickly to the power section" assuming you meant the engine kicks on... that is a tell tale sign of this mechanism at play, and is what makes me think the battery was disconnected.

    You have to read the post...

    Again it only applies if the 12v was disconnected.

    The mechanism to get the computers to relearn has to do with commute style.

    The low mpg mechanism mainly only effects city mpgs and not highway mpgs.

    It basically effects the power you can get out of pure EV mode at city speeds.

    The guy in the Reddit Post confirms he was experiencing the low mpg mechanism I describe and that he fixed it through changing commute style that allowed the ECU'S to relearn to their max mpg state.

    Your computers may have already relearned if you do frequent trips at speeds at 65+ mph.

    Here is a link to a PriusChat post I made describing the same low mpg mechanism as well. I realized the Reddit Post could be glitchy viewed in browser due to the formatting...

    You need to read the whole comment see where I'm coming from.

    Again I still have not confirmed this mechanism exists for sure, but I'm 99% does.

    And nobody else knows it exists but me.

    Which is why the description is so thorough.

    I'm going to need to prove that it exists or they'll all tell me my Prius is functioning completely normally like we did to you in this post.

    You may actually be on the right track, that something is different with your Prius after the brake job, you're just not sure what.

    My post might shed some light on that.

    Posted via the PriusChat mobile app.
     
    #53 TheLastMojojomo, Jul 18, 2021
    Last edited: Jul 18, 2021
  14. jerrymildred

    jerrymildred Senior Member

    Joined:
    Oct 28, 2016
    11,490
    14,095
    0
    Location:
    Tampa, FL
    Vehicle:
    2017 Prius
    Model:
    Two
    @TheLastMojojomo is right. The videos show your car behaving exactly as it should.

    As for the lower fuel economy, that's very likely a result of fiddling with EV mode. That's a great way to kill your MPG numbers. Let the car decide when it should turn the engine on and off. If you run in EV unnecessarily, then you wind up burning extra gas recharging the traction battery.
     
    TheLastMojojomo likes this.
  15. Dvs0999

    Dvs0999 New Member

    Joined:
    Jul 20, 2021
    9
    3
    0
    Location:
    New York
    Vehicle:
    2010 Prius
    Model:
    Four
    Make sure you cleaned very well and greased everything property
     
  16. Nikki CLO

    Nikki CLO New Member

    Joined:
    Dec 28, 2021
    2
    0
    0
    Location:
    Michigan
    Vehicle:
    2010 Prius
    Model:
    Two
    Did you get any resolution on this? Seems I am having a similar issue. 45 mpg prior to 2 weeks ago. Spark plugs, new tires and front brakes replaced. 38 mpg last week and barely 30 this week. They think it’s the new tires and I just can’t believe that it would make a 15 mpg different. Car feels like brake is on and there’s like 2000 lb in the trunk. Lots of drag. Help!
     
  17. james nancy

    james nancy Member

    Joined:
    Aug 10, 2021
    110
    24
    0
    Location:
    suva,fiji
    Vehicle:
    2010 Prius
    Model:
    III
    The new tires will cause the mpg to drop. Is there any slight friction in your brake system? You can feel the temperature of the brake discs, and pay attention to safety conditions. Another thing that may be easily overlooked is the tire alignment problem, which will affect it. Linear acceleration performance and fuel consumption will have a greater impact on short-distance trips and indoor low-speed mpg. You can use a simple method to make a measurement, straighten the tires, if necessary, do this action, straight forward 20 meters, and then back 20 meters , Stop in a place as flat as possible, use a tape measure to measure the distance between the left and right tires at the front of the tire, and then measure the distance between the rear and compare the two numbers. You will know whether they are aligned. The front tire and the rear tire will need 4 lengths.
     
  18. ChapmanF

    ChapmanF Senior Member

    Joined:
    Mar 30, 2008
    23,073
    14,980
    0
    Location:
    Indiana, USA
    Vehicle:
    2010 Prius
    Model:
    IV
    Here is a simple and sensitive test for brake drag.

    Sometimes, if the drag is substantial, you don't even need a sensitive test. Just drive some, then get out, walk around the four corners of the car, and pay attention when you feel your shins broiling.

    But the test above will give you useful information even when the drag isn't nearly that bad.
     
  19. xliderider

    xliderider Senior Member

    Joined:
    Apr 19, 2012
    7,842
    3,099
    0
    Location:
    Honolulu, HI
    Vehicle:
    2011 Prius
    Model:
    Three
    Were the brake caliper slide pins cleaned and lubed?

    Posted via the PriusChat mobile app.
     
  20. Mendel Leisk

    Mendel Leisk Senior Member

    Joined:
    Oct 17, 2010
    54,474
    38,106
    80
    Location:
    Greater Vancouver, British Columbia, Canada
    Vehicle:
    2010 Prius
    Model:
    Touring
    Rear brakes for sure won't touched? They can be messed up during assembly, cause excessive drag. Just for giggles, try:

    1. Chauk front tires (to prevent the car shifting excessively).
    2. Raise rear of car, with parking brake off.
    3. Try spinning the rear wheels: with a good push they should continue to spin about 2 revolutions. If they stop abruptly when you let go they're messed up.