Hybrid battery problem or just its cooling fan?

Discussion in 'Prius c Care, Maintenance and Troubleshooting' started by Tipjar, Apr 10, 2026 at 5:11 PM.

  1. Tipjar

    Tipjar Junior Member

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    My wife's 2015 Prius C with only 60,000 original miles has been showing the "Check hybrid system stop the vehicle in a safe place immediately" warning message off and on for the past two years. It always happened on particularly hot days which makes sense because the temp sensors around the hybrid battery trigger the dash warning. We learned to keep the intake and exhaust vents for the battery unobstructed. The hybrid battery's cooling fan has always been clean, I've even completely dismantled it to be sure, and it didn't need taking because part there was dirt or debris inside it. The warning message won't appear if I happen to have the access panel to the regular battery off (which is right next to the hybrid battery). Presumably because the battery is getting all the cooling it needs.

    Now I'm running down my options. I've seen the hybrid battery's cooling fan working at a low speed on occasion. Is it possible for the fan to be bad but still operate at a low speed? Can I check the health of the hybrid battery's cells with an obd reader and Dr. Prius software or does it really require a shop with better equipment to determine if one or more cells are bad?
     
  2. BiomedO1

    BiomedO1 Senior Member

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    You need to first get us the trouble codes it's throwing; because it's obviously intermittent. The trouble codes will tell you what the ECU doesn't like, because right now your just guessing. The OEM clearly states to keep those vents clear, just because your doing that now, doesn't mean that you haven't already damaged the traction pack. This is like, not doing an oil change until the oil lamp lights up. Is the AC working and do you use it? Set the HVAC to auto and 70 degrees to see if the problem reoccurs.
     
  3. Tipjar

    Tipjar Junior Member

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  4. JamesSmith66

    JamesSmith66 New Member

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    Dr. Prius is more than enough to catch the specific error code. Once you pull that data through the scanner, it'll be pretty obvious what's actually triggering the warning.
     
  5. bisco

    bisco cookie crumbler

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    a prius aware scanner should give you more detailed codes. look into autel maxi 200. idk if it will work with the c or not.
    dr prius will give you module voltages. it might be worth opening up the battery and looking for corrosion
     
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  6. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

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    A good scanner is the right start to troubleshooting.

    It's easy to say that a 2015 should be due for replacement about now; that's a pretty normal expectation. But maybe not. A report from a good prius-aware scanner should help.

    Good luck!
     
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  7. Tipjar

    Tipjar Junior Member

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    After checking compatibilities online I ordered a VeePeak Bluetooth 5.0 Plus which should arrive on Monday. The proof will be in the diagnostic of the cells. Other than that, upon watching Dr. Prius videos online two things caught my attention. One is an ability to set what temperature the hybrid battery's cooling fan kicks on. I've always felt it activates too late and at too little speed. The other is an ability to wipe codes. I'm guessing that means codes actively displaying and not the log of their history. I'm a little bit hopeful since the codes have never come up in cooler weather. And wonder if corrosion on the hybrid battery pack's busses may be a culprit.
     
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  8. rjparker

    rjparker Tu Humilde Sirviente

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    A P0A80 is enough for Toyota to replace the hybrid battery if it is still under warranty. It does not mean its too hot because those are separate codes. It means the modules are unevenly worn which reduces capacity for the whole assembly.

    If they were too hot the controllers would speed up the fan. Dr Prius can increase fan speed but it goes back to controller logic the minute you don't have Dr Prius connected and in the foreground.

    So called "rebuilders" use data Techstream or low cost bluetooth apps like Dr Prius or Car Scanner have as a starting point to teardown and test individual modules with custom loads, chargers and voltmeters. Modules that are bad are replaced with better used modules. It can take weeks to do it right at home with minimal tool investment. Even then, the user may have to teardown and replace more bad modules yearly.

    Or they buy "rebuilt" assemblies with "warranties" but still play wack a mole with poor reliability unlike the first ten or fifteen years.

    Bus bar corrosion can be a problem and good "rebuilders" will replace them.

    Want "forget about it" reliability for your wife? I know I do. Which is why I bought a new oem pack years ago.
     
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  9. Kingsway

    Kingsway Active Member

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    Perhaps better than just using Dr Prius to get an error code - might be to use Dr Prius to record a log file as you do a nice long drive.

    On varied roads, up and down hills and at slow an high speed. Then email yourself the resulting log which you can easily upload as a file to an AI - I've used both Grok and chatGPT - which will give you a detailed, and expert report on the condition of the pack and any problems it may have. As a relative novice at this sort of thing, I found this very useful and very educational!

    Even if you are not in a position to service the pack yourself, it should give you enough insight to judge whether or not to believe a diagnosis you may subsequently get from a 'pro' ? Also, try uploading to more than one AI, as they vary in the style of their reports and one might be better or more easiiy interpreted than another! A print-out might also be a good guide for anyone who does look at the pack for you.
     

    Attached Files:

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  10. Tipjar

    Tipjar Junior Member

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    Wow, thanks for the suggestion. Interesting reading that Grok summary.
     
  11. rjparker

    rjparker Tu Humilde Sirviente

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    IMG_1123.jpeg
    Got to be kidding...