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Jumped car off rear 12V.....how bad is it??

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Aaron Davis, Jun 7, 2023.

  1. Aaron Davis

    Aaron Davis New Member

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    This is my first post and I apologize if the topic has been discussed in depth....I couldn't find any specific info. I have a 2005 and 2006 and the 2005 recently lost a cell in the hybrid battery. I've replaced a couple cells in that battery over the last few years and it isn't a big deal so I ordered one and went about installing it. The cell installation went fine and everything we well until I got in to start the vehicle. That's when I realized that I had forgotten to disconnect the 12V battery, and with the hatch open it had drained it. No biggie, I thought, since it was right there exposed I'd just hook up my charger and get it running. Well, I didn't realize that you aren't supposed to jump a Prius directly off the battery. So my question is........how much damage did I just do?

    The instrument cluster lights up and looks normal except there is no speed number. Obviously there is a red triangle and other yellow lights and the center display says "there is a problem". The power button light is red/orange and the engine doesn't start. I've used my bluetooth/cellphone scanner and it says no codes detected.

    Any idea what I can do/try to get this thing working? Is there a fuse or something that blows when someone is an idiot and jumps the 12V directly or does it do way more damage? Any idea why it doesn't show codes on my scanner. Thanks for ANY and all help/info.
     
  2. JC91006

    JC91006 Senior Member

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    There is no problem jump starting a Prius but there is a problem if you cross your cables. No damage is done if you do it correctly.

    Maybe the car has other issues, possibly with the rebuilding process of the HV battery or the installation.
     
  3. SFO

    SFO Senior Member

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    Welcome to PriusChat!!
    Have you fully charged the existing 12v battery, and what voltage are you measuring at the jump points under the front hood?
    Have you tried power cycling the vehicle twice?
    When you lose 12v or disconnect the 12 battery the ECUs (computers) will clear the stored obd2 codes, try scanning again and post the results in this thread. Which device or app are you using, as you may need to upgrade to a fully compatible scanner/app or use techstream.

    FYI : you're moderated until you've posted 5 times.
     
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  4. Aaron Davis

    Aaron Davis New Member

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    Thanks for the responses!!

    I was worried when I started searching last night and saw a post or two about "bricking" the car if you jump directly off the 12V. I definitely didn't reverse the jumper leads so as long as its ok to jump directly off that battery I feel better.

    I feel pretty confident that the HV battery is assembled correctly but will verify all connections. This is the 3rd time I've had to replace a cell so I'm getting fairly good at it. My scan tool doesn't show a code, but I was able to check all the cells and everything looked good and balanced....even the new cell I installed.

    Any info on how I "power cycle" the vehicle? I pulled the 12V last night and had it on a charger overnight. The charger showed it as "good" and fully charged this morning, so I quickly hooked it up to see if my problem miraculously disappeared but it was exactly the same. Still has red triangle, no number for speedometer and display says "there is a problem".

    I'm using the Torque app with the Prius package. Its worked great previously and hasn't had any problems detecting and clearing codes.
     
  5. broski

    broski Junior Member

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    any chance you don't have the orange plug seated correctly?
     
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  6. Aaron Davis

    Aaron Davis New Member

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    @broski I will check again, but I thought you could only plug that thing in the "right" way? And if the little "lever" lifts up it should be seated correctly right? I'll definitely look at it though and see if I can find a problem.
     
  7. pasadena_commut

    pasadena_commut Senior Member

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    Definitely check the voltage on the 12V both with no load and with a moderate load (headlights on). If it is dropping below 11V replace the battery.

    Also, just try to start the car again. I recall seeing strange issues just from removing and replacing the 12V battery at the first start. It did something like what you are describing at the first attempt. Power down, power on again, and it was fine then and for all subsequent starts.
     
  8. PriusCamper

    PriusCamper Senior Member

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    Can you please confirm that this isn't just symptoms of a bad combination meter that needs its capacitor upgraded? Once you confirm that we can talk about other things to check.
     
  9. Aaron Davis

    Aaron Davis New Member

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    @PriusCamper I'm not sure how to confirm it's not the combination meter, but I can say the car was running and driving fine last week and got the usual red triangle. I checked codes and had P3019 which I verified by check voltages (block 9 was dropping to 14V under load). I had to drive it a couple times after the first red triangle and it would drive fine but throw the code every so often, which I would clear and it would be fine. I parked it and waited for the cell to show up.

    I finally got time Tuesday night to tear into it and when I got in to move it of course had the red triangle, so I cleared the code and backed the car up to my shop to make it easier to work on (100').

    The 12V battery definitely died while I was working on the HV battery and it was my fault because I didn't disconnect it and had the hatch/doors open for a few hours. When I tried to start the car after re-installing the HV battery I discovered the dead 12V and tried jumping it....which led me to this thread. I'll test more stuff this evening but I'm glad that it doesn't automatically "BRICK" a prius if you jump it directly to the 12V battery. That's what had me super freaked out.

    I'll update with what I find. Does anyone know of a way to "factory reset" prius in case my code reader can't detect/reset the codes? I mean if that dang red triangle is on the dash it should show a code, but it isn't.

    Thanks.
     
  10. sam spade 2

    sam spade 2 Senior Member

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    How exactly do you expect him to know that ???

    IF.....the battery went really LOW and then was jumped from another source without completely disconnecting it first......
    there may be some "trash" left over in some of the computers from trying to operate at the low voltage.

    I suggest that he completely disconnect ALL 12 V inputs for about 10 minutes and then reconnect the battery and try again.
    Assuming that the battery is now charged up to more than 12.5 volts.

    It is possible that a single deep discharge like that actually KILLED the 12 V battery and no amount of charging
    will bring it back.
     
  11. Aaron Davis

    Aaron Davis New Member

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    Well I think that my 12V is toast. Its at the autoparts store getting tested but even after charging all night (and my charger saying it was good) it immediately said "needs charged" on their load tester. I expect to get a call in less than an hour that I'll be buying a new battery.

    So that will be the challenge. I'm going to pull the HV orange plug and leave it overnight. Hopefully that will clear any crappy stuff in the computers from trying to use that bad battery. Or is there any other "trick"??

    Again.....thanks everyone for the help with this.
     
  12. edthefox5

    edthefox5 Senior Member

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    Don't ever do anything directly off the 12 volt battery in the hatch.

    Its not very accessible for a jump and Toyota already gave you a safe tool to jump start or charge or check the battery voltage using the front jump point. Many a Prius has been significantly damaged futzing around in the dark hatch trying to do a jump.

    Don't ever check the 12 volt battery voltage at the battery. That's meaningless. Always check at the front jump point because that's all that matters is the voltage reaching the front main fuse box. The 12 volt battery has to go thru many connections and a 100 amp fuse and a big long cable underneath the car before it gets to the front fuse box. You instantly check all those connections at the front jump point.
     
  13. SFO

    SFO Senior Member

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    Power cycle means on/off, any time you lose 12v or disconnect the battery the vehicle will need two (2) cycles to become "ready" again.
     
  14. Aaron Davis

    Aaron Davis New Member

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    Got the verdict this evening....my 12v battery is bad. They stock an AGM battery for $183...is that the way to go or is there a better option. Would a bad 12v battery cause the weird issues I have?

    Thanks @SFO . I'll try the "power cycle" tomorrow when I get the new battery. I disconnected the orange plastic "plug" on the hybrid battery tonight and will leave it disconnected until tomorrow evening. That should clear everything and start fresh....right?
     
  15. dolj

    dolj Senior Member

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    That will actually do nothing.

    But if you do, make sure you execute step 3 - Push the lever down as shown below:
    Prius Gen 2 Safety Interlock.jpg
     
  16. MCCOHENS

    MCCOHENS Member

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    I have charged a weak battery at the battery and jumped from there also. Never had an issue.
     
  17. sam spade 2

    sam spade 2 Senior Member

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    That's complete and total BS, Ed.
    What is meaningless is your constant BAD advice.
     
  18. Aaron Davis

    Aaron Davis New Member

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    @dolj well dang it....I was hoping that would hard reset everything and give me a fresh new car. :D Thanks for the info on the orange plug....that step 3 is easy to miss.

    @MCCOHENS Thanks for the info. I was SUPER worried when I initially Googled and saw the whole "bricking the car" stuff. Whew!!
     
  19. rjparker

    rjparker Tu Humilde Sirviente

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    It is easier to "brick" the car in the rear if you inadvertently reverse polarity the jump or charger. Same as if you jump from the front using another car and your buddy screws up at the jump car end. Or if you take the 12v battery out and somehow put it in backwards. Only takes less than a half of a second at reversed polarity.

    The smart way to jump is with a lithium jump module that automatically verifies proper polarity before it energizes the jump. Which is what all the roadside services use.

    So its not about where you jump 12v, its how you do it.
     
    #19 rjparker, Jun 8, 2023
    Last edited: Jun 8, 2023
  20. Aaron Davis

    Aaron Davis New Member

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    @rjparker I completely get it. I was very careful about getting polarity correct....which honestly is pretty simple based on the large red plastic cover over the + (POSITIVE) terminal. Hopefully I'll get this new good battery installed and everything will be good again.
     
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