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Gen 2 12v battery went from 12.8v down to 5.8v overnight. Just had it load tested yesterday.

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Longinus876, May 27, 2023.

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  1. bisco

    bisco cookie crumbler

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    or get a proper code reader for prius
     
    #21 bisco, Jun 12, 2023
  2. Longinus876

    Longinus876 Junior Member

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    I'm hesitant to do that for several reasons. Number one being that my experience with the local dealer has not been good. After an oil change, I found a quart of dirty oil in the crankcase. Don't trust them. I need some info before I bring it down there. It's likely that they'll try to sell me the moon and I need to be ready for a discussion.
    Wanna take a couple of questions? No prob. either way.
    I have what appears to be about a 1 amp draw on the 12 volt. What would you say the likely culprit is? I don't hear the relays clicking over on the HV batt.
    The 12 volt passes a load test but is on a trickle charger because of the draw .
    Would using an OBDII be of use in this case? If so, what one would you suggest?
    Thank you.
    Are some of them not compatible with hybrids? Scanned it w/ a Foxwell and got P0A80 generic code. Could mean anything from dead 12 volt battery to a bad haircut.
     
    #22 Longinus876, Jun 12, 2023
    Last edited: Jun 12, 2023
  3. rjparker

    rjparker Tu Humilde Sirviente

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    A voltmeter from chassis to the negative terminal of the battery will read zero volts unless the negative battery cable has been disconnected. That is an invalid voltage test. Sometimes that configuration is used to measure amps or milliamps, eg current being drawn ftom the battery. Generally as a parasitic current drain test.
     
    #23 rjparker, Jun 12, 2023
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  4. Longinus876

    Longinus876 Junior Member

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    Yes, in series. I did that.
     
    #24 Longinus876, Jun 12, 2023
  5. bisco

    bisco cookie crumbler

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    most readers are incompatible with prius. they often pick up a few codes, but not all and zero sub codes, which are important to aid diagnosis
     
    #25 bisco, Jun 12, 2023
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  6. Longinus876

    Longinus876 Junior Member

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    As I expected. I see Dr.Prius/Hybrid and TorquePro out there. The compatibility issue is not reall really highlighted in the info they supply. Used a Foxwell and got the P0A80 code but nothing else.
     
    #26 Longinus876, Jun 12, 2023
  7. bisco

    bisco cookie crumbler

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    tech stream has everything, but is complicated to set up.

    i have read here that there is one off the shelf reader that works, but i can't verify it or remember the name.
    i think @Tombukt2 uses it
     
    #27 bisco, Jun 12, 2023
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  8. Longinus876

    Longinus876 Junior Member

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    Do you remember if it's a BlueTooth or anything else about it? I thrive on failure.
     
    #28 Longinus876, Jun 12, 2023
  9. bisco

    bisco cookie crumbler

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    i'm pretty sure it's a direct hook up to the obd port. tom will hopefully be along to help out.
     
    #29 bisco, Jun 12, 2023
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  10. Longinus876

    Longinus876 Junior Member

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    Excellent. We'll see. I may have to break my wallet.
     
    #30 Longinus876, Jun 12, 2023
  11. bisco

    bisco cookie crumbler

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    it's not cheap keeping an old car on the road, but newer ones are even more expensive
     
    #31 bisco, Jun 12, 2023
  12. Longinus876

    Longinus876 Junior Member

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    I just noticed that half the draw on the 12 volts is the ABS jack.
     
    #32 Longinus876, Jun 12, 2023
  13. Longinus876

    Longinus876 Junior Member

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    True.
     
    #33 Longinus876, Jun 12, 2023
  14. bisco

    bisco cookie crumbler

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    have you measured the draw with the car off? the inverter can usually keep up with it when driving
     
    #34 bisco, Jun 12, 2023
  15. Longinus876

    Longinus876 Junior Member

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    Yes. Always off as the car won't start and we have the triangle. I don't get any sound from the relays clicking over to start the HV battery hook-up.
    Just to catch you up, I have found that half the power is being drawn from the ABS module. I unplugged it and the draw went down to about .5 amps.
     
    #35 Longinus876, Jun 12, 2023
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  16. pasadena_commut

    pasadena_commut Senior Member

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    Were any of the doors open? That can draw a surprisingly large amount of current, in fact, right around 500 mA. When I do this sort of testing the car is off, the doors are closed and the hatch is open (to allow access to the 12V battery). However, the hatch has a carabiner stuck in the slot to emulate the loop from the hatch, which looks like "hatch closed" to the car. Also, wait a very long time to test after the car is turned off or the driver's door opened. Stuff is turning on and off for several minutes after those events.
     
    #36 pasadena_commut, Jun 12, 2023
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  17. Longinus876

    Longinus876 Junior Member

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    YES!...All the dopey modules need to go to sleep. Have I overlooked that? Probably. I'll go out to the driveway and check.
    BTW, I'm getting quite a spark when I reconnect the negative ground to the body. It certainly looks like there is a major draw. One sec. Okay, I checked. The car's been untouched for about 45 min. Still pulling .65amps. That's cookoo. Must be something on.
    So many fuses and relays. I should just pull the mall and see what happens. Maybe disconnect the jumper lug in the fuse box. Gotta start somewhere.
    Keep thinking. We'll find it soon.
     
    #37 Longinus876, Jun 12, 2023
  18. Longinus876

    Longinus876 Junior Member

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    I checked with Leo and Sons. They only fix helicopters and Corvettes. No, I'm lying. I'm in NY. We have no honest people here.
     
    #38 Longinus876, Jun 12, 2023
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  19. PriusCamper

    PriusCamper Senior Member

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    Makes me wonder how much that 500mA drain can be reduced by switching to LEDs?
     
    #39 PriusCamper, Jun 12, 2023
  20. PriusCamper

    PriusCamper Senior Member

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    #40 PriusCamper, Jun 12, 2023
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