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SoC drains to two bars every other night

Discussion in 'Gen 2 Prius Technical Discussion' started by goitalone, Aug 11, 2011.

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  1. goitalone

    goitalone Member

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    I bought a 2004 Prius the other day and realized, seemingly every other night, that the SoC goes from almost all blue bars to two brownish bars when I start the car the engine kicks in and drains my average MPG by like 1 MPG before it charges back up.

    Also, it seems the engine runs at really high RPMS (not sure how to check RPMs BTW) and runs fairly loud at first...even while accelerating after the SoC gets back up, it seems loud, but not as much as when the SoC bars are low.

    I am pretty sure this isn't normal, is it?
     
    #1 goitalone, Aug 11, 2011
  2. seilerts

    seilerts Battery Curmudgeon

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    At two bars, the car preferentially charges the battery via the engine. On a cold start, the battery is preferentially used to push the car forward, until the engine warms up.

    If you are worried about the HV battery, listen for the battery fan. Its input duct is on the back seat, passenger side, near the seat belt. Any time you hear the fan running, count on the engine to be working overtime. Try to keep your battery cool. Hard to do in FL I know.
     
    #2 seilerts, Aug 11, 2011
  3. vertex

    vertex Active Member

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    How many miles are on the car?
    You should run through 1 or 2 tanks of gas and check your fuel consumption, you should get over 40 mpg. Also, your 12 volt battery should not be original, it is in the back on the passenger side.
     
    #3 vertex, Aug 11, 2011
  4. goitalone

    goitalone Member

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    Okay I will listen for it, but parking the car for a 24 hour period in general though, in say max. outside ambient temps of 100 F shouldn't drain the battery bars from almost fully charged to 2 brown bars should it?
     
    #4 goitalone, Aug 11, 2011
  5. goitalone

    goitalone Member

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    Getting close to 109,000 miles.

    I am on my first full tank and been trying hard to get the best MPG and so far I have gone almost 200 miles, 3 of 10 fuel bars have been depleted and I have 45.2 MPG average on trip meter.

    How do I know if the 12v is original or not? I will check that as well.
     
    #5 goitalone, Aug 12, 2011
  6. seilerts

    seilerts Battery Curmudgeon

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    Okay, let's take a step back. When the car is off, the main battery is completely disconnected. It can't be drained. What can change, though, is how the state of charge is measured. When you parked the car, it had calculated the SoC as value X. When you return to the car, conditions have changed: the temperature is different, voltage may have fallen a bit if left long enough due to surface charge dissipation, etc. The hv battery ecu then recalculates the SoC based on present conditions. On top of that, for the first 30 seconds of being Ready, the battery is the only thing that moves the car, and this demand causes the SoC to fall rapidly.

    If you are getting 45 mpg and not hearing the battery fan running, and not getting red triangle warnings, your hv battery is okay.
     
    #6 seilerts, Aug 12, 2011
  7. TonyPSchaefer

    TonyPSchaefer Your Friendly Moderator
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    If I understand correctly, it sounds as though your battery is draining when you first start the car and start driving. I hope that's correct. I also hope it's correct, though you didn't say it, that you leave a parking lot (or driveway) and hop onto a street with a speed limit greater than 35mph.

    Because if those two things are correct, I can assure you that this is normal.

    When you first start the car, the engine is warming up and running rougher than normal in order to heat the engine and the catalytic convertor. In this case, the car likes to use the battery to power the car. When moving quickly, the battery drains faster. If driven fast enough for long enough, the battery gets down to 2 bars. Personally, I let the engine warm up under light load by driving the long way through my work parking lot before hopping on the 45 mph street. At home, I have to move through a suburb so that's not a problem.

    As for every other day, well that part I can't explain. Are all days identical in time of day, speed, etc?
     
    #7 TonyPSchaefer, Aug 12, 2011
  8. 2009Prius

    2009Prius A Wimpy DIYer

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    Let the engine warm up while the car is still in "P" (park) and shift to "D" (drive) only after the engine sound changes or shuts off automatically. This removes the unnecessary stress on the HV battery and also helps overall fuel economy. Good luck!
     
    #8 2009Prius, Aug 12, 2011
    1 person likes this.
  9. kenoarto

    kenoarto Senior Member

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    do not know if there is ever a good reason to idle a Prius. Just drive if you want to charge the battery.
     
    #9 kenoarto, Aug 12, 2011
  10. 2009Prius

    2009Prius A Wimpy DIYer

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    HV battery is not being charged during S1 unless the car is in "P" (park).
     
    #10 2009Prius, Aug 12, 2011
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  11. goitalone

    goitalone Member

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    No, I meant even before I begin to drive the car, as soon as I start the car and glance at the SoC, it has drained/recalculated or whatever (overnight) from basically a full charge, to a 2 bar charge on the display.

    It happens like every other day, NOT every single time. I sleep during the day and go out at night usually, so maybe that has a bit to do with it.

    I will listen for the fan and see if I hear it. Other than that, I guess everything is okay :confused:
     
    #11 goitalone, Aug 12, 2011
  12. goitalone

    goitalone Member

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    One other thing:


    When I let go of, or press too quickly on the gas, I feel a significant lunge/chug as if I have a broken motor mount.


    Does a Prius have motor mounts, or something that can go bad that could immitate a broken motor mount?

    My mothers Prius does not do this, so I think something is off on mine.
     
    #12 goitalone, Aug 12, 2011
  13. TonyPSchaefer

    TonyPSchaefer Your Friendly Moderator
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    Do you know the history of the 12v battery?
     
    #13 TonyPSchaefer, Aug 12, 2011
  14. goitalone

    goitalone Member

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    No idea or info about the 12v. And other than regular maintenance from both of the two previous owners, this 1st owner detail was shown on the Carfax report:

    04/15/2006

    Recommended maintenance performed
    Brake light switch replaced
    Parts ordered
    Engine/powertrain computer/module reprogrammed
    Four wheel alignment performed

    What symptoms would I see if the 12v battery were failing?
     
    #14 goitalone, Aug 12, 2011
  15. TonyPSchaefer

    TonyPSchaefer Your Friendly Moderator
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    People have reported all kinds of silliness resulting from an end-of-life 12v battery. Things you wouldn't normally think. I'm really not mechanically inclined so I'm sure someone can provide better info.
     
    #15 TonyPSchaefer, Aug 12, 2011
  16. 2009Prius

    2009Prius A Wimpy DIYer

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    #16 2009Prius, Aug 12, 2011
  17. northwichita

    northwichita .

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    Does a Prius have motor mounts,
    My mothers Prius does not do this, so I think something is off

    The motor mount that would control engine 'roll' is located underneath the middle of the engine/transaxle. Drive the car up on ramps to look at it. Perhaps the rubber is worn.
    Believe it's called a control arm.
    https://www.toyotapartsbarn.com/toyota-prius-parts.html?gclid=CO_h5MyqzaoCFQQI2godqnAnzA
    Click on engine, then mounts.

    And about the battery 'discharge', I've never noticed my prius HV battery SOC dropping to any extent when the car is off. More importantly , how to 'fix' this, my guess is to drive the car more-- for several hours at a time--- take a trip somewhere, and see if that helps.
     
    #17 northwichita, Aug 13, 2011
  18. goitalone

    goitalone Member

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    Okay, thanks for all the info you guys....I'll check all these things out.

    I seriously think something is bad wrong though.
     
    #18 goitalone, Aug 13, 2011
  19. edthefox5

    edthefox5 Senior Member

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    Your right something is wrong. Bought my 07 new and there is never a difference between the charge of the Hybrid Battery from shut off at night to the next morning or afternoon or even after not driving it for a weekend.
    It holds a charge very well.

    You may have a bad cell or very corroded battery string interconnections.
    Both somewhat common for the age of your car. Lots of posts about both.
    Also check 12 volt battery ( not really connected but does crazy things when bad) If suspect replace immed.
    Check for Inverter coolant condition and if the Inverter coolant pump is even running.. Check to see if your VIN is on the PUMP recall notice.
     
    #19 edthefox5, Aug 15, 2011
  20. Spcalan1

    Spcalan1 New Member

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    Same here... not completely dead, but I know the high rpm, loud noise, and 1mpg average..... But again, 10 mins later I will have a fully charged battery pack.
     
    #20 Spcalan1, Aug 15, 2011
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