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Prius 2001. New owner. 12v battery is draining even with another good battery jumpered on. Why?

Discussion in 'Generation 1 Prius Discussion' started by RathlinPhil, Oct 20, 2020.

  1. RathlinPhil

    RathlinPhil Junior Member

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    As soon I turn on the ignition it pulls the aux battery way down below 12v. I've used different batteries which I know are good but it pulls them down rapid...
     
  2. bisco

    bisco cookie crumbler

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    try putting a good battery in directly
     
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  3. RathlinPhil

    RathlinPhil Junior Member

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    Thanks for replying,

    I did that yes. connected a big 120 AH leisure battery directly, charged and steady 12.9 v. It drew down to below 12v within 30 seconds of switching on the ignition. The car is issuing a P3125 code. The car won't start , it just switches every thing on and off when i try.
     
  4. bisco

    bisco cookie crumbler

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    something is definitely draining it then. sounds like a short, or bad pc board. to narrow it down, you'll probably need tech stream
     
  5. sam spade 2

    sam spade 2 Senior Member

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    120 AH is not really a "big" battery.

    You have a car that is almost 20 years old.
    There could be a LOT of things wrong with it, starting with the HV battery.
    My guess is that it is not worth fixing.

    But if you insist, you very likely need professional help.
     
  6. Rmay635703

    Rmay635703 Senior Member

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    Bad inverter

    I would start with the hv battery and see what SOC it’s at.

    also I have a 40amp 12 battery charger, recommend you attach a similar to keep it running, might let the smoke out of the short
     
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  7. ChapmanF

    ChapmanF Senior Member

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    "big" depends on what you're talking about, right? a house? 120 AH is more than four times the 28 AH battery that originally came in Prius Gen 1. It's nearly three times the 48 AH battery Toyota later listed for it as an upgrade.
     
  8. TMR-JWAP

    TMR-JWAP Senior Member

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    It drew down to below 12v within 30 seconds of switching on the ignition.
    it just switches every thing on and off when i try.


    Assuming all your 12v battery connections are good, it would take an incredibly large load, in a Prius, to drop a 120AH 12v battery from normal operating voltage down to a voltage that is so low it making relays open.

    I ran into a similar problem when troubleshooting a car.
    The 12v battery in the car was at 0 volts, so I installed one of my backups. Upon trying to start the car, the 12v system immediately went under a huge load and dropped the battery into the 10 volt range. The only way I could get the load to stop was to remove the ABS relays. Once I removed the relays, I was able to actually continue troubleshooting.

    The owner failed to mention they had jumped the car with polarities reversed. This blew the main fusible link and a couple fuses in the underhood jump point. This also caused the brake accumulator pump to run non-stop, even when the accumulator was fully charged, deadheading the pump/motor. This put a huge load on the 12v battery. I don't know exactly why, as I never dug deep into it, but I just assume one of the blown fuses caused a loss of pressure measurement/indication, causing the pump to run.

    Once I found the blown link, replaced it and the fuses, all those problems went away.

    Try pulling the ABS relays and then see if the load goes away.

    Maybe you have something similar going on. There aren't many things on a Prius that can draw that much current.
     
    #8 TMR-JWAP, Oct 21, 2020
    Last edited: Oct 21, 2020
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  9. RathlinPhil

    RathlinPhil Junior Member

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    Hi there folks, Thanks for all the replies/ suggestions. That gives me a few more things to check over. I'll give a bit more back round for clarity.
    I bought the car a week ago from a lady doctor who owned it in England, She had moved back home to Portugal and the car had been layed up for a couple of months and the 12v battery was dead, She said the car had been driving fine when it was left there, although she had to replace the 12 v twice in three years under warranty from toyota (which gives me the suspicion something was wrong). Her friend managed to jump start it and drive it (turtle mode) to local mechanic who kept it for weeks and done nothing but tried and failed to charge it's totally dead 12v battery. SO anyway i took a chance and bought the car for scrap price, had it shipped from the mechanic in England to Ireland and then then towed it on and off another ferry to the island where I live.

    The car only has 89 000 miles so i thought i'd take a chance on it, nearly every car I've every had is twenty years old or more so I'm only used to old machines with plenty things wrong with them.

    So far I got rid of the dead toyota 12v, (which is still under warranty) bolted on two heavy cables to the top of it's own terminals so i could connect a large 12v battery with big terminals (i have a few of these 120AH deep cycle batteries use for an off grid setup.) I understand that you should use the correct size AGM for the car and I will, if i get the car running but for now surely any good 12v with capacity should okay for testing right?

    I checked the 100 Amp fuse under the hood in the fusebox and it seems intact .
    After reading on here that a flat HV problem can cause all sorts of problems i moved on to that.
    I took the big battery out and stuck it on the workbench. It measures 300v at the output terminals and 7.85 on each cell. That seems okay ? Gona put it back in today.

    One piece of vital information is that, as the lady was having 12v trouble for a few years i think the car has been jumped quite a few times (there was a jump pack in the boot). It could be quite possible it had been connected reverse polarity by someone.... who knows.......

    I'm gona check the connections to and from the inverter and remove the abs relay as suggested.
    Also I can buy a salvaged inverter for 100 pounds so I think i'll get one anyway.

    CHEERS PHIL.
     
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  10. RathlinPhil

    RathlinPhil Junior Member

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    What I consider a big battery:
    } hurts your back, legs and arms to lift
    } Big massive sparks fly out when you do something wrong
    } Cost a big heap of money
     
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  11. ChapmanF

    ChapmanF Senior Member

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    Even the 28 Ah gen-1 original will make those if provoked.
     
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  12. RathlinPhil

    RathlinPhil Junior Member

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    yes, I suppose you're right.... I've heard of people welding with mobile phone batteries....Rmay635703 reckons i should try and produce smoke. Exciting these Priuses....
     
  13. RathlinPhil

    RathlinPhil Junior Member

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    There did appear to be a pump stuck on for the brakes. I could here it running when i tried to start the the car, I struggled for a while trying to remove the main ABS solenoid from the drivers side fuse box, opened the clips but the thing wouldn't budge. I ended up loosening the whole fuse box to get a look underneath and check for melted wires, but all seemed okay there. Anyway after leaving the car switched on and jumpers connect connect to another running vehicle so the battery voltage stayed about 12.8 the noise stopped and the current drain on the 12v stopped. I cleared the codes with an android app and then i got the car to start. I let it run and could see it was charging the 12 v steady at 14.2 it was also charging the HV battery which SOC was okay at 52% . I took it for a drive and it charged the HV battery fine . Then when i switched the car off again and tried to restart it started draining the 12v down and wouldn't restart again. red triangle and P3125 back again. The app I'm using won't give me any sub codes just parameters. got tech stream on the laptop but no cable yet. I'm just glad to hear the thing running at all to be honest.

    If it is a short, do you think it is likely it could stop shorting when the car is running? I got the car going today and once running the 12 v battery was sitting nice and steady at 14.2. could it be dc -dc 12v charging system is putting enough out to keep the voltage steady? I still didn't get any sub codes......
     
    #13 RathlinPhil, Oct 26, 2020
    Last edited by a moderator: Dec 8, 2020
  14. bisco

    bisco cookie crumbler

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    yes, the charging system can disguise a parasitic drain on the battery, depending on how big
     
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  15. sam spade 2

    sam spade 2 Senior Member

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    Yes. Once running, any vehicle will be charging the battery.......and you are NOT seeing the battery voltage but the charging system voltage.

    AND.....not being able to hold a charge is the way most automotive batteries fail.
    You likely have a bad battery, that is no longer capable of supplying the power needed to do what it is supposed to do, regardless of how much it is charged.

    While that might LOOK like a higher than normal drain or a phantom drain while off, it really isn't.
     
  16. RathlinPhil

    RathlinPhil Junior Member

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    I would love to believe that but I tried another 110 Amp/hr battery in today(fully charged and good condition) and it can't start the car without being jumpered to a running vehicle.

    The car seems to drive fine once going, then when I switch it off the voltage of the battery drops to 13v as you would expect, but when I immediately try and switch the car back on, the voltage drops to below 12 in seconds. Sure sounds Ike a dud battery but it ain't.

    I'm metering at the battery with a multimeter ,but the 12v supply voltage stated by the ECU is always 0.5 - 0.7v lower.
    I tried pulling fuses , the only one that made any difference was AM2
     
    #16 RathlinPhil, Oct 27, 2020
    Last edited: Oct 27, 2020
  17. sam spade 2

    sam spade 2 Senior Member

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    I'm sorry I wasn't clear enough.
    That comment was regarding the voltages that you measured and NOT about the specifics of your present situation, necessarily.

    It does indeed appear that you have a somewhat unusual problem.

    P.S. Jumping to a RUNNING vehicle is not a good idea, no matter what kind of vehicles are involved.
     
  18. RathlinPhil

    RathlinPhil Junior Member

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    Thanks for the reply, and I appreciate your insight.
    What are the risks involved in jumping off a running vehicle.
    Can it cause particular problems with a Prius?
    Right now it's the only way I can get the car to run. It will stay in ready mode all day with no problem.
    I managed to put a new code on by pulling out fuses. This code now won't clear.
    • DTC: C0278
    • Description: Hydraulic modulator solenoid valve relay - circuit open
     
  19. vvillovv

    vvillovv Senior Member

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    C0278 TOYOTA: Code Meaning, Causes, Symptoms, & Tech Notes
    are there other of the same solenoids in the box you can use to check if that solenoid is bad, as a first step in diagnosing that one code?
    I've only driven the Gen1 for a weekend when the were first available locally 20 years ago.

    Does this code clear? If yes has it come back?
    P3125 - Toyota Prius Hybrid Fault Code Diagnosis - Rennacs
    did you ever get the sub code(s)?
    what are you using to get and clear codes?
     
    #19 vvillovv, Oct 28, 2020
    Last edited: Oct 28, 2020
  20. sam spade 2

    sam spade 2 Senior Member

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    A bit worse than most maybe.

    The biggest danger is if a mistake is made........OR the sick vehicle has a dead short in the 12 V battery or it's connections.
    Then a HUGE spark and fire might result......and end up with TWO dead vehicles instead of one.

    If you MUST do that, make all of the cable connections first and then start the donor vehicle AFTER you are sure there is no smoke happening.
     
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