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HV battery weak but B1271 is only code

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Maureen G., Nov 4, 2021.

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  1. Maureen G.

    Maureen G. Junior Member

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    I had a rebuilt battery installed 2 years/20k miles ago. One cell failed a few months after installation, had it replaced. Now I'm getting quick drainage of the battery. Just a 10-mile trip uphill will take it down to 2 red bars.

    I ran the Techstream Health Check and the only code showing is B1271 which one site says may be caused by:
    Faulty Combination Meter Assembly (Meter ECU),
    Combination Meter Assembly harness is open or shorted, or
    Combination Meter Assembly circuit poor electrical connection

    Does this make sense? Current mileage is 126k. Thanks
     
    #1 Maureen G., Nov 4, 2021
  2. JC91006

    JC91006 Senior Member

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    It makes perfect sense that an old HV battery would be weak. There's not much you can do, unless you buy equipment to recondition it. Otherwise wait for it to fail and install a new battery. The new batteries will cost more but will last around 10 years.
     
    #2 JC91006, Nov 4, 2021
  3. dolj

    dolj Senior Member

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    If you are experiencing intermittent failure of the combination meter (CM), it makes perfect sense in that the first option is the most likely. It is a common fault and is easily fixed by replacing a failing capacitor on the CM PCB if you are ok with board-level electronic repairs.

    It doesn't help any with the hybrid vehicle battery though.
     
    #3 dolj, Nov 5, 2021
  4. Maureen G.

    Maureen G. Junior Member

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    I donʻt know how to do board-level repairs so would take it in. But youʻre saying this is unrelated to the battery, meaning there is no faulty reading of the battery level if thereʻs intermittent failure of the meter.

    In which case I would ask a follow-up question: Why am I not getting a battery code? Does the battery have to be discharged/low when I run the health check? The way I knew which cell to replace on the rebuilt battery was that I got a detailed readout of each cell's performance with the battery code, but I don't see anything like that right now.
     
    #4 Maureen G., Nov 6, 2021
  5. mr_guy_mann

    mr_guy_mann Senior Member

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    Assuming that you are using the same scantool as earlier, you're not getting codes because the battery ecu isn't seeing high enough voltage difference between battery "blocks" for long enough time. So the ecu doesn't think there's any problem.

    Question, is this hill one that you drive up regularly? ie- have you gone up this same hill many times before and have had consistently different battery gauge readings? By itself I wouldn't be surprised by the gauge going down if you drive up a steep hill long enough at a high speed.

    It can take more power than the engine can provide alone so the Prius uses the HV battery and motors to help out, but if you keep going then eventually the battery will discharge. A fully charged HV battery can propel the Prius by electric motor power for maybe 1 to 1-1/2 miles on flat roads.

    Posted via the PriusChat mobile app.
     
    #5 mr_guy_mann, Nov 7, 2021
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  6. Maureen G.

    Maureen G. Junior Member

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    @mr_guy_mann Yes, this is a hill I drive up regularly, I live on the side of a volcano in Hawaii and everything is either up or down from here. About 6 miles in either direction. It didn't drain the battery doing this climb for the past couple of years with the refurbished battery, so I guess it's getting weaker but not enough to alarm the ecu just yet.

    Hate to have to wait for the details before I get the warranty coverage (again!) but the way I understand it is he'll need the specific data to match voltages in adjacent cells. :(

    Unless that's not correct, and I can get some help from the refurbisher now?

    I took a pic of the 2 red bars the other day, after it had discharged the battery just sitting overnight again (this has happened 2 or 3 times now). But then I went down the hill, charged it, and came up without a problem. That is the easier direction, though. Not so steep.

    Thanks for any more light you can shed on this!
     
    #6 Maureen G., Nov 9, 2021
  7. mr_guy_mann

    mr_guy_mann Senior Member

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    If the battery State Of Charge goes down noticeably overnight, then you might want to see what the HV battery block voltages are in the morning - before going into "ready" mode. See if any are way off.

    Posted via the PriusChat mobile app.
     
    #7 mr_guy_mann, Nov 9, 2021
  8. TheLastMojojomo

    TheLastMojojomo Active Member

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    This Battery behavior of dropping low to 2 bars is somewhat normal for long trips up hills. The effect can definitely be amplified by a weaker HV Battery and other factors like AC use.

    I answered a similar post to yours awhile back and it may give some insight. See my Post describing how long uphill treks can result in loss of power and cause low HV Battery charge.

    Your issue could partially be caused by a weak HV Battery, but also might be normalish behavior.

    Edit: I see you say it discharged overnight, which is not normal. It may indeed be the HV Battery in it's way out.

    Posted via the PriusChat mobile app.
     
    #8 TheLastMojojomo, Nov 10, 2021
  9. Maureen G.

    Maureen G. Junior Member

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    @TheLastMojojomo your post was very useful. I usually have the AC on here in Hawaii so next time I go up that hill I'll keep it off and see what happens. I'll also get the CM fixed so at least that is ruled out as potentially being contributory.

    @mr_guy_mann The a.m. weakness (2 bars) is so intermittent it might be a while before it shows up again, but I'll go take a reading tomorrow morning and see what I find.
     
    #9 Maureen G., Nov 23, 2021
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  10. bisco

    bisco cookie crumbler

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    you are probably just hyperaware because it is a refurbished battery with a limited warranty. but in general, you need a code for coverage.
    unfortunately, that is the nature of refurbished batteries. the cells are old, and will continually fail.
     
    #10 bisco, Nov 23, 2021
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