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Prius turns on immediate upon connecting 12v

Discussion in 'Generation 1 Prius Discussion' started by Derek., Feb 22, 2021.

  1. Derek.

    Derek. Junior Member

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    Have a 2005 prius that has had a current draw so I've been disconnecting the 12v, now when I go out to use the car and I connect the battery, even without the key fob in the ignition all the dash lights come on, hv battery fan starts, hear it click, I get the triangle and beep. I was getting a hv battery ecu communication error code thru techstream. I did a search and came up with a thread on here that (gen 1 tho) said the tank pressure sensor shorted and was messing up the ecu. I looked at the wiring diagrams and maybe that's what's happening to me? I checked the IM1 connector and there's mouse piss on it and the pins have that blue tarnish. Here's a diagram I pieced together to help myself out. I'd pull the connector at the tank for the pressure sensor but I can't get to it. I have a lift but the car doesn't move with that stupid parking lock and I can't get it into the garage with a lift. I can't tow it with my truck either. Seems easiest just to cut that vcc line going from pin 9 IM1 or release the terminal from the connector if I can (save me from soldering it later). Thoughts?

    that other thread No start due to P3106, ECM -> HV ECU communication failure? | PriusChat
     

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    #1 Derek., Feb 22, 2021
  2. Derek.

    Derek. Junior Member

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    oops I put this in the wrong forum.
     
    #2 Derek., Feb 22, 2021
  3. ChapmanF

    ChapmanF Senior Member

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    I seem to remember cases of this happening if the 12 v power was lost while the car was ON. Didn't complete its normal shutdown sequence, and actually tries to resume where it left off when the 12 v power returns.

    It's generally not so realistic to expect that what happened to somebody else is going to be exactly what has happened to you, especially something as peculiar and specific as the issue that other member had in a thread for a different generation of Prius. At most, you might want to ask yourself if the same kind of thing might be part of your own picture, and try to find out if it is or it isn't, such as by backprobing at the ECM to see if its sensor reference voltage is out of spec.

    If you do find that it is, then you probably want to check all the sensors supplied by that output (if there are more than one) to see which one is at fault, rather than assuming it would be the same one as in that other post. And if your meter doesn't confirm that anything of that sort is happening, then you can scratch that idea off your list of possibilities (before you've gone and cut any wires!), and keep on toward finding what the real problem is.
     
    #3 ChapmanF, Feb 22, 2021
  4. Derek.

    Derek. Junior Member

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    That was it, runs good now. Cutting the positive power to the tank pressure sensor alleviated the issue. Not very good design if a flawed sensor takes down the electrical system.
     
    #4 Derek., Feb 23, 2021
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  5. Derek.

    Derek. Junior Member

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    Driving it around for a while, twice it did something very strange. Engine raced and I actually had to step on the brake because the car started accelerating hard by itself. I pulled over, turned off the car, let it sit for a couple minutes, then it worked fine again. I'm thinking there's something going on also or maybe even the only cause at connector J14 which supplies the ECU and the throttle positions sensor. Or like you mention something else fed by that bus. Maybe a bad TPS or the "w-5 water valve" I've updated the above drawing to include this new development

    prius chat shrinks the image so here's the original https://i.postimg.cc/KmSnbgm0/hv-com-err-1.png
     

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    #5 Derek., Feb 24, 2021
    Last edited: Feb 24, 2021
  6. ChapmanF

    ChapmanF Senior Member

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    You can click the link to PriusChat's thumbnail image and see the 958✕960 version.

    Can you capture the misbehavior in a Techstream data log?
     
    #6 ChapmanF, Feb 24, 2021
  7. Derek.

    Derek. Junior Member

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    Its tough because it happens maybe once maybe in a few hours of driving and my laptop doesn't have enough battery power to do more than a few minutes of logging (with how long it takes to get everything set up)
     
    #7 Derek., Feb 24, 2021
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