B mode

Discussion in 'Prime Main Forum (2017-Current)' started by Jon Cryer, Jul 20, 2019.

  1. Jon Cryer

    Jon Cryer Junior Member

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    Is there any downside to driving in "B mode" while driving in town with 25 and 35 mph speed limits?

    Posted via the PriusChat mobile app.
     
  2. schja01

    schja01 One of very few in Chicagoland

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    I’m unable to engage cruise control while in B mode fwiw.
     
  3. eskudo12791

    eskudo12791 Junior Member

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    "The "B" position favors lower gears, too, but for a totally different purpose. Just as you might shift a conventional transmission to Low on a long downhill grade; you can shift into the "B" position to increase engine drag and help slow"

    are you doing down hill in town?
     
  4. schja01

    schja01 One of very few in Chicagoland

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    Brake lights do not display when in B mode. Could be a downside when that car/truck behind you pays your trunk an unexpected visit.
     
  5. Jon Cryer

    Jon Cryer Junior Member

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    I never use cruise control in town.

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  6. Jon Cryer

    Jon Cryer Junior Member

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    Very few hills but lots of stop signs and red lights.

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  7. Jon Cryer

    Jon Cryer Junior Member

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    No brake lights seems to be the main downside.

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  8. ice9

    ice9 Active Member

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    What about reliability/wear? Excessive downshifting in a manual transmission vehicle is known to decrease clutch life expectancy. Will excessive use of B mode in a Prius degrade or cause premature failure of the M-G or other power train component(s)?
     
  9. schja01

    schja01 One of very few in Chicagoland

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    Since I signed up for State Farm's "Drive Safe and Save" program which has been saving me
    30% on my car insurance I use Cruise Control regularly (28mph+) to inadvertently keep from
    going over the speed limit (which is easy for me to do).
    I use it in traditional (not Radar) mode to keep the car from slowing excessively in non safety related
    situations eg. a car drives across the road in front of you at a safe distance but the Prime still slows
    more (in my opinion) than needed.
    To each his/her own I guess.
     
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  10. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

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    I would anticipate higher fuel use when using B mode for anything other than downhill braking.
     
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  11. Georgina Rudkus

    Georgina Rudkus Senior Member

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    B means engine braking which also means that the ICE is always running in this mode. With the ice running, the car does not go into EV mode and uses more fuel.
     
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  12. Trollbait

    Trollbait It's a D&D thing

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    The parts are moving regardless of shift position. The engine may be spinning for braking, but won't be experiencing near the level on abuse as when gas is being burned.

    For the Prius, yes. For the Prime, only if the battery is fully charged. The Prime makes more use of regenerative braking in B before resorting to other braking strategies.
     
  13. ice9

    ice9 Active Member

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    Yeah. I'm not intimately familiar with the hybrid drive train, but after 10 years of using B mode, my gen 2 started getting intermittent red triangles when decelerating, and there was a noticeable lurch whenever the ice would turn on or off. It felt to me like a clutch on a std transmission going bad. I recently traded in my gen 2 to get a gen 4 earlier this year.
     
    #13 ice9, Jul 21, 2019
    Last edited: Jul 21, 2019
  14. Prius from Dad

    Prius from Dad Senior Member

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    When the Prime is in EV mode with charge remaining in the battery, the ICE does not run in B mode. It will do that in other modes. In EV mode it is not engine braking but motor braking.
     
  15. jerrymildred

    jerrymildred Senior Member

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    The biggest drawback (assuming you're in EV mode) that I know of is that you'll probably use more fuel because you'll coast less. Regenerating is more efficient than friction braking. But coasting is more efficient than regenerating. Of course in HV mode, you'll us a LOT more fuel. I get the bast results by just driving it in D like the manual says to do.
     
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  16. Prius from Dad

    Prius from Dad Senior Member

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    But in EV mode you use no fuel, only battery charge. :confused:
     
  17. ChapmanF

    ChapmanF Senior Member

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    I've never noticed my former Gen 1 or current Gen 3 Prius always running the engine in B. I just checked it again on the way back from lunch; the engine was not constantly running, and the car even made a 70 amp regenerative stop in B without using engine braking at all.

    The B in B mode was surely chosen to bring "engine braking" to mind, as a rough shorthand for what that shift position is used for, but it's nowhere near a complete technical description of what the mode does. Like a lot of things Prius, the car has several strategies for slowing and braking that it can use alone or in combination, and B mode slips in different values for the biases between them.
     
  18. ice9

    ice9 Active Member

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  19. Prius from Dad

    Prius from Dad Senior Member

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  20. jb in NE

    jb in NE Senior Member

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    In a Prime this is not the case. In EV mode with less than a full HV battery, selecting B does not start the ICE but increases regenerative braking.
     
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