Intermittent Negative HV Battery Voltage Readings

Discussion in 'Gen 2 Prius Technical Discussion' started by Carovahokie, Feb 14, 2018.

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  1. Carovahokie

    Carovahokie New Member

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    I have a bit of a ghost / mystery happening with my recently purchased 2005 prius (115,000 miles). When I bought the car, it was having traction battery issues & was throwing the P080 code (I paid very little for the car). I pulled the battery and found significant corrosion of the bus bars, water pooled in the rear fender wells, and a leak in the hatch at the body seam above the hatch hydraulic arms. All of the battery modules tested-out within 0.1 volt of each other. I fixed the leak, cleaned all of the corrosion from the bus bars & sending wires, and reassembled everything. It drove fine for about a month. Since then:

    Occasionally (seems to loosely correspond with rainy days), my car is throwing the red triangle warning accompanied with the P080 code again accompanied with some "jumpiness" in the battery charge monitor on the dash. When it happens, I can clear the code, drive for a few minutes, and then it goes back to normal - no codes & no pending codes. several days or weeks later, it will happen again - same symptoms, same reset, & everything seems to go back to normal. I finally got hold of the torquepro app to monitor the voltage in each battery cell. When the car is operating normally, all modules seem to stay within 0.2 volts or so of each other:
    IMG_3636.JPG

    After several days of driving, the car finally threw the red triangle again (on a rainy day), and this happened:
    IMG_3633.JPG

    A bunch of outrageous negative battery voltage readings. After a reset of the codes & a little bit of driving, everything went back to normal. Any ideas?
     
    #1 Carovahokie, Feb 14, 2018
  2. Prodigyplace

    Prodigyplace 2025 Camry XLE FWD

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    #2 Prodigyplace, Feb 14, 2018
  3. edthefox5

    edthefox5 Senior Member

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    Either you did a very poor job of assembly and still have corrosion or did not torque nuts correctly or you have soft modules. Did you see corrosion from leaking electrolyte? You may have cracked modules. Does the car see a lot of steep hills that’s very hard on the battery. Does the hybrid fan come on during these events?

    Pull it back out and load test all the modules and recharge. Load test is a must to find the weak one.
    No LT its just whack a mole hope it works. Most times it does not. Not for long. The age of the battery almost garantee's it has some soft modules.

    Then assemble correctly and make sure there are no wires that have the slightest bit of corrosion on there ends as corrosion on a connector travels up the wire under the wire coating.

    What is your background concerning something as technical as this?

    Also make sure you clean the battery vent fan motor.

    When you pull it back out take pictures. You should already have many pictures of it.
     
    #3 edthefox5, Feb 14, 2018
    Last edited: Feb 14, 2018
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  4. Carovahokie

    Carovahokie New Member

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    I'm an engineer (not an electrical engineer, but some electrical training that comes along with becoming an engineer) and a DIY guy. I feel comfortable performing this work - I have successfully replaced bad battery modules on two other Gen II priuses (sp?).

    I live in a flat area (beach), do not drive the car in high-demand load conditions and the fan does not come on during these events. I did not see corrosion that I thought was from leaking electrolyte - the corrosion was widespread and appeared to be the result of high moisture conditions (from the leaking hatch). Bus bars before & after:
    IMG_3397.JPG IMG_3399.JPG



    My suspicion since getting these readings has been that there is corrosion further down the wire or further back in the electronics (or some other kind of electrical short). Before I pull the battery again and pursue that route, I wanted to post here to see if anybody had ever encountered a switch to negative voltage readings like this (just in case it was something else or just in case there was something else that I should be doing when I have the battery out).
     
    #4 Carovahokie, Feb 14, 2018
  5. edthefox5

    edthefox5 Senior Member

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    Good experience.

    yes your not alone search the forums the proper code is

    PA080

    P A zero eighty.

    use search forums button up top of page.

    and whats does the buss bars and battery connectors look like? And if widespread corrosion you are leaking electrolyte somewhere. Usually the middle pack under the most heat.

    Pull all the modules out clean and inspect carefully. Bolt it back up and load test them and recharge them. But 2005 is very old battery. Do not charge them unbolted or even loose they will swell and crack.
     
    #5 edthefox5, Feb 14, 2018
    Last edited: Feb 14, 2018
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  6. TMR-JWAP

    TMR-JWAP Senior Member

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    I've seen the weird high negative numbers only twice and never found a 100% definitive cause.

    Not only look at the harness terminals, but look at the plug and the receptacle on the ECU. They are also areas where corrosion occurs.
     
    #6 TMR-JWAP, Feb 14, 2018
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  7. Carovahokie

    Carovahokie New Member

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    I didn't snap a picture of the connecting wires - there was a lot of corrosion at the wire connections that I cleaned with steel wool & vinegar. I did not disassemble the wires from the connectors that bolt to the battery cells - if there is a weak link in my cleaning, that is it (and if nobody points me toward any other leads, that is what I am going to attack next).
     
    #7 Carovahokie, Feb 14, 2018
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  8. edthefox5

    edthefox5 Senior Member

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    I wonder if one module has very bad connection and goes offline for a sec and the ecu interprets that fast drop out swing as a negative going voltage.
     
    #8 edthefox5, Feb 14, 2018
  9. edthefox5

    edthefox5 Senior Member

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    bingo....
     
    #9 edthefox5, Feb 14, 2018
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  10. edthefox5

    edthefox5 Senior Member

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    Should have taken pictures of every single thing on that battery before starting. Take alot of pictures so you know for sure where which wire goes back to.
     
    #10 edthefox5, Feb 14, 2018
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  11. edthefox5

    edthefox5 Senior Member

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    If you strip that wire back from the connector you will see bad corrosion going up the wire for quite a ways. Doesn't really matter at this point its connection is rotted. You just cleaned the outside of the connection. The bolted down connection is worse.

    Good Luck.
     
    #11 edthefox5, Feb 14, 2018
  12. Carovahokie

    Carovahokie New Member

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    In cleaning the wire lead-to-connector interface, would you snip the connector off, pry open the crimp connection, throw away the short wire that is waste, clean everything, and then expose some new wire from under the insulation & re-make the connection, or do I need to try to salvage even the wire that is currently crimped into the connector?
     
    #12 Carovahokie, Feb 14, 2018
  13. Carovahokie

    Carovahokie New Member

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    Or at this point, do I need to just replace the entire wire harness connecting to the battery?
     
    #13 Carovahokie, Feb 14, 2018
  14. edthefox5

    edthefox5 Senior Member

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    It depends.

    See how bad the wire corrosion is. Strip it back and see how far up the corrosion goes. Go to shiny clean wire and crimp on new spade or ringlet if it reaches. If its corroded to long a new wire must be installed of proper gauge. Apply 100% synthetic grease not dino grease between all connections. If you don't the shiny metal connections will corrode again quite quickly. Thats a very tough atmosphere the battery interconnect lives in. Battery gas and galvanization. Even the slightest amount of battery gas will start some corrosion on shiny copper. Patina turns into bad connection. But I'm pretty sure you have a leaking module which will not help corrosion wise.

    Pictures please.
     
    #14 edthefox5, Feb 14, 2018
  15. Carovahokie

    Carovahokie New Member

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    Thanks for the help. I will probably get back into the project this weekend and will let you know what I find / post pictures.
     
    #15 Carovahokie, Feb 14, 2018
  16. edthefox5

    edthefox5 Senior Member

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    Cool good luck. Sounds like just wire cleanup. if you plan on keeping the car I highly recommend a prolong battery Charger/Discharger
    system. I have had very very good results waking my 10 year old bought new battery. Been almost a year and it still looks like new on the battery meter. Lots of us use one on this forum.

    Search prolong battery charger in search forums.

    Prolong Battery Systems. Extending the life of your hybrid. – Hybrid Automotive

    Theres also a very well known and respected engineer on this site who is selling his own system. Looks pretty cool and I would probably buy one from him when mine dies:

    Prius Battery Replacement Kit (GenII/GenIII) with NEW custom cells | PriusChat
     
    #16 edthefox5, Feb 14, 2018
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  17. fotomoto

    fotomoto Senior Member

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    Overall it sounds like you have a very weak battery that will fail come spring or summer once the heat arrives.
     
    #17 fotomoto, Feb 14, 2018
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  18. edthefox5

    edthefox5 Senior Member

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    yep at that age no way around that. One thing I have learned on this site is if you don't load test them your just wasting your time and your back. But its very time consuming.
     
    #18 edthefox5, Feb 14, 2018
  19. Carovahokie

    Carovahokie New Member

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    I like that cylindrical design on the Replacement Kit - I have to think that it would promote better cooling.
     
    #19 Carovahokie, Feb 14, 2018
  20. JC91006

    JC91006 Senior Member

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    It probably doesn't cool any better
     
    #20 JC91006, Feb 14, 2018
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