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Power at 12v but not at front terminals.

Discussion in 'Gen 2 Prius Audio and Electronics' started by BobThePrius, Aug 20, 2019.

  1. BobThePrius

    BobThePrius Junior Member

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    Hello PriusChat! Here is my situation:

    The car has zero power to any electrical function, however, it can be jump-started from the from front terminals under the hood, and all the car will run as normal and display no diagnostic codes (at least according to my bluetooth OBD2 reader.) As soon as the car is turned off however it shows no power to any electrical function. I have searched through this forum but have not found anyone with the same problem that I have (although I could have missed something.)

    Here is what I know so far:

    -The 12v battery is good and only a few months old (displays 12.94 v across the terminals and the guy at Autozone also confirmed the battery is good.
    -Across the terminals, under the hood, only 0.5v show up on my multimeter.
    -I cleaned and tightened all battery connections and terminals, and voltage is reaching the end of the negative cable and the end of the 120a fusible link box on the positive terminal.
    -The 100a fusible link at the front passes a visual inspection and reads about 0.05 ohms on my multimeter.
    -Prior to this issue arising the car had been sitting at airport parking for about 6 days and the car had been resetting the clock and MPG after being turned off, and sometimes instantly restarting after being turned off for about two weeks. From what I have seen on the forums the issues that existed before the car stopped having power have been attributed to faulty grounding or a bad 12v, however, the battery is good and as far as I can tell the grounding wire from the terminal is securely attached to the body.
    -My OBD2 reader is reporting 151.v when I have it jumpstarted and idling.
    -The car I jumpstart the Prius from does not need to be on for the Prius to come back to life, the leads simply needs to be connected to the terminals in both cars.
    -Trying to jumpstart from the trunk does nothing (which is to be expected if 12 volts are detected at the back but not at the front.

    Information that seems less prevalent but may be important to someone more knowledgeable than myself:
    -Some water has been pooling in the interior body paneling below the battery compartment.
    -The 12v was replaced in March of this year by the previous owner.
    -I have had this car for a few months but have put some serious mileage on it.
    -Whoever replaced the previous 12v apparently did not replace the hydrogen vent as I found it down by the spare tire. I immediately replace it when I noticed this about a week before this issue came up.

    My plan of attack is to continue to check relays, fuses, and circuit breakers between the front and back end according to wiring charts I obtained from this forum. Any advice or suggestions on where to look for blown fuses /lose wires / broken wires would be greatly appreciated!

    Many thanks,
    -Prius Bob
     
  2. bisco

    bisco cookie crumbler

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    welcome!
    if you're positive the negative to ground is clean and tight, i would try another battery just to eliminate the possibility. how old is it? even though it was replaced, i would check the date
     
  3. davecook89t

    davecook89t Senior Member

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    You may want to take a look at this thread:

    P0AA6, car won't start unless jumped, other codes | PriusChat

    I would suspect you may have corrosion in the area of your System Main Relay, given that you have had water intrusion in the past, and the 12V does not seem to be able to connect to your HV battery. Before poking around in there, though, I would recommend that you take all the safety precautions necessary for working with high voltage, and I think it is essential that you get a hybrid compatible scan tool to see what codes are being reported before anything else.
     
  4. Skibob

    Skibob Senior Member

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    So your checking the voltage on the battery fuseable link at the far end, not the end that connects to the battery and your getting full voltage? I think the only thing between that and the front jump point is the wire itself. Have you inspected the wire for damage?
     
  5. BobThePrius

    BobThePrius Junior Member

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    I took up as much of the interior paneling as I could and did not see any visible damage to the wire, although I cannot be sure I did not miss anything.

    The battery has a sticker that says 3/19, although I am not sure if that was the install date or the manufacturing date. Besides voltage is there anything else I should look for in a 12v?

    I am not sure I have the right tools or experience to go looking around in the high voltage battery, I might turn it over to a pro if that seems to be the issue. Are there any symptoms that corrosion in that area would produce? I will look into a hybrid scan tool, do you have any specific recommendations?
     
    #5 BobThePrius, Aug 21, 2019
    Last edited by a moderator: Aug 21, 2019
  6. bisco

    bisco cookie crumbler

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    you need a load test. auto parts stores will do one for free and give you a printout. otherwise, you can buy a load tester, or hook up a couple of headlight bulbs and watch the voltage

    what brand battery? toyota truster have a date code, not a date
     
  7. PriusCamper

    PriusCamper Senior Member

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    Interesting situation... If jump starting it from another vehicle causes the car to work fine and no error codes, then there's nothing wrong with the high voltage system, ECU's, Etc.

    Easiest fix is if you bought an Optima battery because they're awful and I blame them for everything! But the symptoms don't really point to that.

    As you go about checking fuses, you can also unplug stuff and look inside those plugs for greenish dirty / corrosion damage. Also for a few bucks you can by an auto test light where you plug one end to ground and use the other end to poke the connectors or cable to isolate where the 12v current first drops out of the circuit after it comes out of the battery.

    Lastly, does this vehicle have a clean title or is it salvage from a flood / any signs of water damage?
     
  8. TMR-JWAP

    TMR-JWAP Senior Member

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    The (+) cable from the battery goes directly to the jump point under the hood. Do a continuity check on the cable. If you're feeling crazy, temporarily run a long heavy gauge wire from the battery + terminal to the jump point and see if your problems go away. 12v+ at the battery post and 0.5v at the jump terminal just means you have an open in the circuit somewhere.
     
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  9. Skibob

    Skibob Senior Member

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    I thought that too, but wouldn’t Toyota put some kind of fuse at both ends? If the cable failed while the car was running the wire would be live from the jump box to the failure point, not good. The wire is a good idea. At least you will know it the cable from the battery to the box then.
    Edit: I forgot about the 100 amp main in the fuse box. That would cover that end.
     
    #9 Skibob, Aug 22, 2019
    Last edited: Aug 22, 2019
  10. TMR-JWAP

    TMR-JWAP Senior Member

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    I have a complete wire harness from a disassembled 2007 in my garage. One end of the cable attaches at the 12v battery + terminal (in actuality, it attaches to the black plastic assembly, which in turn clamps to the post) and the other end attaches directly to the jump terminal. Nothing in between except copper and insulation.
     
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  11. Skibob

    Skibob Senior Member

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    So the other fuse is the 100 amp in the box then?

    If he is measuring 12v at the cable end of the battery fuseable link and 0 at the jump points it has to be that cable. 100%.
     
  12. Skibob

    Skibob Senior Member

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    @BobThePrius show us a picture of where you are testing the 12v at the battery.
     
  13. TMR-JWAP

    TMR-JWAP Senior Member

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    here's what I would do (with no tools required other than a meter)...

    With black lead on (-) terminal of battery and red lead on battery (+) terminal...should be 12v. If not = dead/bad battery.
    If it is 12v, then....

    With black lead on body of car and red lead on (+) battery terminal...should be 12v. If not = bad (-) cable or connection.
    If it is 12v, then...

    With black lead on battery (-) terminal, poke the red lead through the 12v (+) cable insulation near where it comes off the battery fuse holder assembly. Should be 12v. If not = bad connection or bad component at the (+) terminal, or between the terminal and where you touched the cable with the red lead.

    If it is 12v, then...
    measure with black lead on body of car and red lead on the under hood jump terminal. Should be 12v. If not, verify your black lead is correctly making contact with the chassis. If so, then the cable has an open in it somewhere between the previous 'poke' and the jump point.
     
  14. BobThePrius

    BobThePrius Junior Member

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    The battery is 12v (see pictures below) and with the black lead on the very end of the ground wire it is 12v. However, when I put the black lead on the body close to the connection I get 0 volts is this how it should be? I assumed that the ground was past that body panel, so I didn't think about not getting voltage on the body but this could be where the connection is broken. As a note, I also don't get voltage on the bolt that holds the ground wire to the body, and I also have not been able to unscrew the bolt, it is weirdly tight.

    Thanks for the advice!

    Should I physically break through the insulation with the red lead
     

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  15. BobThePrius

    BobThePrius Junior Member

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    Here is the battery, and it is a little harder to see, but I included a picture of me getting voltage at the end of the fusible link box.
     

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  16. Skibob

    Skibob Senior Member

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    I can’t tell from the picture, are you checking the voltage at the big wire or from of the white connectors?
     
  17. BobThePrius

    BobThePrius Junior Member

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    I'm getting the voltage inside the fusable link box where the larger white connector and wire plug into the fusbable link box (at least that is what the schematics I found online called the black box attached to the positive terminal.)
     
  18. bisco

    bisco cookie crumbler

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    it seems to me that if you have voltage at the neg terminal, but not at the ground, your whole problem is between the two
    think you're gonna have to bust that bolt and start over
     
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  19. TMR-JWAP

    TMR-JWAP Senior Member

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    You cannot put the black lead on a painted surface, which it appears to me you are doing when you get the zero reading after checking the (-) cable where it attaches to the car body.

    Put your black lead on the bolt head I placed an arrow near. That bolt should be plated metal and will conduct. Use that as your ground point/black lead for all your measurements in that area.

    172712_body.jpg
     
    #19 TMR-JWAP, Aug 22, 2019
    Last edited: Aug 22, 2019
  20. Skibob

    Skibob Senior Member

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    I don’t know if that will show if the fusible link is bad or not. That connector powers the brake capacitor box (that black box). That might have its own fuse as having brakes is considered important by Toyota. You need to check the main wire itself, no other wire or connector will do.