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

2010 Gen 3 Prius 12V battery intermittent charging

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by William Geesaman, Jul 17, 2022.

  1. William Geesaman

    William Geesaman Junior Member

    Joined:
    Jul 17, 2022
    7
    1
    0
    Location:
    Virginia, USA
    Vehicle:
    2009 Prius
    Model:
    N/A
    2010 Prius (V?) 230,000 miles.

    This is my sisters car (located in UT), so I have not been able to lay my hands on it directly. This is what I know:

    Just fixed traction battery and car is working fine now, BUT randomly STOPS charging the 12V battery while driving. When this occurs, the 12V battery will steadily drop voltage and has been seen as low as 11.6V via the monitor on the dash and Torque App. The car will "recover" eventually, but we cannot figure out why it stopped charging OR why it starts to charge again!!! When the voltage drops low, almost everything on the dash is lit up JUST LIKE a typical low 12V battery issue. The battery is NEW (replaced just a couple months ago) when we fixed the traction battery and this problem has persisted since then. The car was off the road for over a year due the traction battery problem, but bad cells have been replaced and that part is working great now. Using Torque, we can also see the voltage and note that it does not always match the reporting on the car dash (see photo). Sometimes it is exactly the same. I think this is an important finding, but don't know for certain.

    So, BIG issue is the 12V battery intermittent charging (I think) and the other issues are symptoms. Has anyone seen this problem OR have any ideas on what could be causing this issue?

    RANDOM THOUGHTS:

    The offset in two voltages leads me to believe this is a bad connection somewhere in the harness. Since the car is in Utah and I am in Virginia, I can't easily trace this out myself. I don't even know where to get good wiring diagrams to troubleshoot this issue.

    If there is another thread on a similar topic, please point me in that direction. I have searched, but maybe I am looking for the wrong thing.

    I have two Prius' myself (2009 and 2010), with nearly 400,000 combined miles. I am an Electrical Engineer with an automotive repair and electrical design background, so can get into advanced troubleshooting and repairs without feeling over my head. Long-distance troubleshooting is just making this hard.

    I want to get this car back on the road RELIABLY as soon as possible. It has not left her stranded YET, but I don't want that to happen either.

    I appreciate you reading this far. Please ask questions and I will provide more information as needed.

    TorqueVsCarVoltage.jpg
     
  2. tankyuong

    tankyuong Senior Member

    Joined:
    Nov 9, 2012
    1,555
    659
    0
    Location:
    Central MO
    Vehicle:
    2012 Prius c
    Model:
    II
    i would try another new battery
     
  3. Tombukt2

    Tombukt2 Senior Member

    Joined:
    Nov 29, 2020
    7,797
    1,349
    0
    Location:
    Durham NC
    Vehicle:
    2009 Prius
    Model:
    Base
    So that's the car screen 13.7 and your computer at 14.5 but is that computer connected right back at the battery or just in the system through the veci OBD port . If you turn the car unready does that 14.5 turn to zero and then when you ready it goes right back to 14.5?
     
  4. Mendel Leisk

    Mendel Leisk Senior Member

    Joined:
    Oct 17, 2010
    54,480
    38,108
    80
    Location:
    Greater Vancouver, British Columbia, Canada
    Vehicle:
    2010 Prius
    Model:
    Touring
    To achieve the bold text, starting with car off: push start button twice, with foot off the brake pedal.

    At least I think that's the objective, to have most of the car's systems up, but the engine not kicking in. Don't leave it thus for too long, it will run the battery down.
     
  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
    get tech stream
     
  6. William Geesaman

    William Geesaman Junior Member

    Joined:
    Jul 17, 2022
    7
    1
    0
    Location:
    Virginia, USA
    Vehicle:
    2009 Prius
    Model:
    N/A
    This is the second new battery. This battery holds a charge and load tests fine. The prior new one did not.
     
  7. William Geesaman

    William Geesaman Junior Member

    Joined:
    Jul 17, 2022
    7
    1
    0
    Location:
    Virginia, USA
    Vehicle:
    2009 Prius
    Model:
    N/A
    The top one is the car (while running) and the bottom one is using the Torque App (connected through OBD2. I will check the "unready" voltage this evening.

    Key point it that the vehicle voltage has been as low as 11.6V after steadily dropping from a full charge, then it will suddenly start charging and get back to a full charge. It was doing this every few weeks, but the other day it happened 4 times on a one hour trip.
     
  8. Tombukt2

    Tombukt2 Senior Member

    Joined:
    Nov 29, 2020
    7,797
    1,349
    0
    Location:
    Durham NC
    Vehicle:
    2009 Prius
    Model:
    Base
    I guess there's a circuit in the inverter that handles this. And I guess if it was intermittent or starting to fail this kind of thing can happen certainly is in the fuse as that would be blown or not generally not intermittent. I'm running around with it AGM battery that will never go over 11.9 volts sitting when it has the 14-5 coming to it from the inverter and the car ready well it shows the 14-5 obviously. But the minute you turn it off let it sit 10 12 minutes it'll go to 11.9 and be at that 12 hours in the morning.
     
  9. ChapmanF

    ChapmanF Senior Member

    Joined:
    Mar 30, 2008
    23,073
    14,982
    0
    Location:
    Indiana, USA
    Vehicle:
    2010 Prius
    Model:
    IV
    In every Prius where I've compared, the voltage reading shown on the MFD's Vehicle Signal Check screen is a good fraction of a volt lower than what you might measure elsewhere, including at the battery or at the OBD-II port. I pretty much always write that as "good fraction of a volt" to avoid pinning it down further. I'm not sure I've seen it quite as high as 0.8 volts before, but certainly 0.5 to 0.7 wouldn't surprise me a bit, so seeing yours makes me more likely to say "meh, guess it can be 0.8" rather than assuming something is wrong.

    I think the ADC that measures the voltage for the Vehicle Signal Check screen is just inside the MFD, and is measuring the voltage that reaches it, at the end of the various voltage drops on the supply paths to the MFD and to the ADC within it.

    The OBD-II port has battery voltage brought to pin 16, and Torque is almost certainly showing you that voltage, as measured by an ADC inside your dongle.

    Have you not seen any warning lights or trouble codes? The DC/DC converter (the part of the inverter assembly that's responsible for the car's 12 volt supply and charging the 12 volt battery) can shut down for various reasons, such as when it overheats. A common reason is a failure of the electric pump in its coolant circuit. Some trouble code (like P0A93) would be expected in that case.

    There's a kind of persistent belief on PriusChat that there is a 'typical low 12V battery issue" that just makes dash lights and trouble codes meaninglessly pop up. You can fall into that thinking yourself, not bother to read the codes, and say it's "JUST LIKE a typical low 12V battery issue", and that's how that belief stays alive and keeps spreading.

    But you're better off just reading the codes. It is likely you will find codes pointing the way to what the trouble is. Yes, if you wait for the voltage to get low enough, there will be additional codes telling you that. (You can see the thresholds for setting those codes in the repair manual; for many of them it will be around 10 or 9.5 volts, as measured on board in the affected ECU.)
     
    William Geesaman likes this.
  10. tankyuong

    tankyuong Senior Member

    Joined:
    Nov 9, 2012
    1,555
    659
    0
    Location:
    Central MO
    Vehicle:
    2012 Prius c
    Model:
    II
    would try a third
     
    William Geesaman likes this.
  11. 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 wonder if a new defective 12v could have an intermittent interior short?
     
    William Geesaman likes this.
  12. Mendel Leisk

    Mendel Leisk Senior Member

    Joined:
    Oct 17, 2010
    54,480
    38,108
    80
    Location:
    Greater Vancouver, British Columbia, Canada
    Vehicle:
    2010 Prius
    Model:
    Touring
    A lot of battery retailers have electronic load testers. Maybe at point of sale they should hook them up, see where the battery's at, in front of the customer. Good for both parties.
     
  13. William Geesaman

    William Geesaman Junior Member

    Joined:
    Jul 17, 2022
    7
    1
    0
    Location:
    Virginia, USA
    Vehicle:
    2009 Prius
    Model:
    N/A
    Thank you all for your patience. My sister has been dealing with other issues and just got back to me tonight.

    More information: 12V battery was replaced early this year (under warranty from parts dealer) just over 6 months ago. Since replacing the traction battery bad cells and balancing the traction battery, the 12V battery has been replaced two more times under warranty. The replaced batteries were all load tested and failed. Well, after 3 weeks of sitting because she is afraid to take it any distance from her house, the 12V battery is dead and the car won't start again. If this is a faulty battery, it is the 3rd dead AGM in just over 6 months. This is far outside "normal" and something must be killing these batteries. The last time we replaced it, I had her put an ammeter inline with the battery to see if there were any high parasitic loads that did not go away. There were not, but we will have to check that again.

    Needless to say, no more testing happened today. Hopefully tomorrow ...

    This is exactly what she is going to do tomorrow ... again. It will be dropped off for a charge and load test.

    Once it is up and running again, I will have her take it for a ride and get all the current codes off the system. More to come.
     
  14. ChapmanF

    ChapmanF Senior Member

    Joined:
    Mar 30, 2008
    23,073
    14,982
    0
    Location:
    Indiana, USA
    Vehicle:
    2010 Prius
    Model:
    IV
    My guess is still that the progress on resolving this issue will really begin when somebody takes the trouble codes seriously.
     
  15. bisco

    bisco cookie crumbler

    Joined:
    May 11, 2005
    107,571
    48,862
    0
    Location:
    boston
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    are there trouble lights? i don't see anything mentioned
     
  16. bisco

    bisco cookie crumbler

    Joined:
    May 11, 2005
    107,571
    48,862
    0
    Location:
    boston
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    what battery brand?

    do you leave torque connected all the time?
     
  17. William Geesaman

    William Geesaman Junior Member

    Joined:
    Jul 17, 2022
    7
    1
    0
    Location:
    Virginia, USA
    Vehicle:
    2009 Prius
    Model:
    N/A
    Interstate ... battery tested BAD and 4th one is on order. It won't be in until Wednesday.

    No, nothing is connected when the car is off.
     
    bisco likes this.
  18. William Geesaman

    William Geesaman Junior Member

    Joined:
    Jul 17, 2022
    7
    1
    0
    Location:
    Virginia, USA
    Vehicle:
    2009 Prius
    Model:
    N/A
    I appreciate the comment on using the codes, and totally agree that they generally provide the most insight. I have done a lot of automotive work over the years and depend on them for most all troubleshooting. Codes have not turned up positive leads on this problem to date. Besides that, I cannot currently read anything until the car is able to start again. 3rd battery tested bad today.

    The 4th new battery is on order and will not be in until mid-week. When it is running again, I will have the codes pulled and post them here. Unfortunately, if recent history is any indicator, I suspect the car will run just fine when the new battery installed. Give it a little time and whatever killed the prior 3 batteries will begin to take it to the grave as well.
     
  19. ChapmanF

    ChapmanF Senior Member

    Joined:
    Mar 30, 2008
    23,073
    14,982
    0
    Location:
    Indiana, USA
    Vehicle:
    2010 Prius
    Model:
    IV
    It was this:

    Then later:

    When that happens, often the best thing to do is just take the codes you have and put them in the post, rather than leaving everyone else only your own conclusion that the codes haven't turned up leads. What doesn't look like a positive lead to you could still ring a bell for somebody else, but it can't if it's not in the post.

    Codes are generally readable with the car IG-ON (two button pushes, no brake); starting isn't required.

    The repair manual even mentions some obscure method, involving the driver door courtesy switch IIRC, for waking up the ECUs to connect a scan tool without going IG-ON. I don't think I've ever done it, but I do remember reading it, for some generation anyway.
     
  20. bisco

    bisco cookie crumbler

    Joined:
    May 11, 2005
    107,571
    48,862
    0
    Location:
    boston
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    sometimes, leaving a reader hooked up to the obd when the car is ready can cause problems. idk why, but it has been documented.
     
    Foxglove likes this.