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Prius help! Is my battery toast?

  • #1
    Registered Users Posts: 942 ✭✭✭ hoodie6029

    My 2006 Prius (285,000km) has been sitting for 4 months since I haven't been using it. I started driving it again in the last week. The 12V battery had been losing it's charge completely after sitting for a few days since last year so I replaced this with the same Yuasa unit that came out of it.

    Now I have been getting the red triangle, VSC, yellow brake warning and MIL lights.

    I've cleared them by disconnecting the 12V but they come back after a few minutes of driving.

    The hybrid battery charges and discharges very quickly now too and the cooling fan, that I don't think I've ever heard running, is running a lot now too.

    Do I just need to clean out my cooling fan will I have to replace the battery?

    I see if I can get it into the mechanic this week to read the actual codes coming up.

    Thanks in advance


  • These cars is designed for driving not storing. Only keep one thing on mind if garage offers the replacement battery, the replacement battery can have similar problems thanks for age and long time storing on warehouse. There is even companies who offer re-manufactured units but all cells is old. They mix and match units to get balanced. Still old cells... So think before you buy the battery, is it worth it. May be cheaper is to cut the losses and sell the car as is.

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  • The battery cooling fan is only coming on because of a battery fault , unfortunately in the traction battery.

    I pulled one of these apart a good few years ago and replaced 2 under voltage cells from a scrap battery.

    as far as I remember I only used a crappy cheap multimeter to tell me 26 of the individual cells were 28.5 v and 2 were something like 14 or 16 v. So easy physical diagnosis.

    swapped 2 cells out and happy days , all done with a 10 mm and 12 mm socket and no other tools and about 3 hrs labour .

    pretty scary until you realise, that once you pull the big orange bulky fuse/breaker the battery pack becomes fairly benign.

    apparently I got lucky , as other lads on the internet would state that all cells needs to be rebalanced which is a time consuming and technical process.

    any way there’s lads in Limerick(DoneDeal) will supply a balanced refurb battery for about 600 euro and swapping out is about 2 hrs, for the complete unit rather than going to the full strip as I did.

  • Cheers for the replies, had a look on Prius Chat and it all seems to be pointing towards battery failure. I'll check out those guys in Limerick and stick an update up with how I get on.

  • Now you can sell the good remainig cells by 400eur, good business! Do not dump all of that, there is many good cells left. Congratulation! Now you figured out how donedeal guys operate. Nothing is new, only old mix and match cells

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  • The success was short lived. I’d done a bit 100km and just as I was getting home the car juddered and lost power. It limped into the driveway and then the same lights came on, VSC, triangle, brake warning and check engine.

    Disconnected the 12V battery this morning and reconnected after a few minutes. Left the car idling and after about 10 minutes the lights came back in the dash. The fan was blowing to cool the battery but not loudly.

    When I popped the bonnet, the engine sounded like a diesel! I give up…I’ll see if I can get a mechanic to look at it now.

  • Who made the initial diagnostics? Swapnostics is the most expensive car repair option (no joke).

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  • Dr Prius app told me that one module was gone on my original battery. Whole host of other codes on the new battery.

    A lot of googling and priuschat searching and it pointed to corroded wiring...somewhere. Pulled the battery ECU out of the 'new' battery and it was fried. 3 or 4 pins heavily corroded or missing.

    Swapped the ECU and connector from the original battery to the new one and it's been working fine so far. Fingers crossed it lasts more than 100KM this time!

  • Even uber does not ask so much money for 100km

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  • Don't talk to me...hopefully I never have to update this....

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  • No, it was not joke. We help you if we can. Always challenge, never easy

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  • Had to replace the 12v battery myself from leaving it sitting too long - Car is not getting much use lately. 120Euros for a battery :(

    So this time I also installed a bluetooth 12v battery monitor - it reports back to my phone the voltage on the battery (20 pounds on amazon). Nice.

    Dont know if the battery I got was a dud - but the 12V battery goes from full charge(12.55+v) to red (12.03v flat) in about 8 or 9 days doing nothing just sitting in driveway.

    “Roll it back”

  • I knew you were joking. Stupid internet, can't pick up my tone 😁 Should've put a smilie on that that last post

    I had to replace the 12V recently to. A Yuasa was the only one the motor factors said was suitable for it since the hybrid is a stop/start system in some ways, cheaper batteries aren't sutiable.

  • Yuasa is very good battery. Only remember to disconnect it, if you do not planning to drive over 100km.

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  • I got the VSC warning in the middle of changing the brake fluid on my RX400h. Thought I had fried something with the spurious programming unit.

    Turned out I was only getting 8 volts from the 12v battery.

    Car had been starting OK but these normally put very little demand on the 12v battery which probably had been poor for a while.

    New 12v battery and all problems solved.

  • This is just from my observations:

    I would say any 12V should be fine - The only thing that's really important is the battery has an Air Vent and its connected - so any fumes/gas from battery leave the car - not stay in the cabin with you.

    From what I can see now Im monitoring the voltages - the 12V battery is used only for powering the car before the car ignition is switched on.

    so...for powering..

    1. the door locks
    2. booting the computer system

    once the center display is on - its computer is booted - and all power comes from the traction battery - even when prius ignition is not in Drive (ie. powered on without foot on brake).

    At this point the 12v battery is just trickle charged.

    Now if the car is in Park - the petrol engine will kick in occasionally to assist charging the 12v battery.

    “Roll it back”