Gen 1 Turtle mode-warm weather

Discussion in 'Generation 1 Prius Discussion' started by dabard051, Sep 17, 2025 at 6:50 PM.

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  1. dabard051

    dabard051 Tinkerer-in-Charge

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    03 Prius in FL, has been running fine. Until today, when just out of the driveway the Turtle Mode light came on and the Battery charge indicator on the LCD display indicates 100% charge. Usually it's between 20% and 80%. This showed 100%.
    Techstream shows no codes that I could find. Traction battery voltages range from 15.08 to 15.77.
    In Turtle Mode, there is no reverse as only the electric motors are available for reverse. So if the traction battery is unavailable, the car can only go forward.
    It was not unusually warm today (mid 90s).

    Any suggestions? Will put a charger on the 12v battery tonight, altho I think that's a long shot.

    <edit> while writing and posting, I let the car sit in the shade of my driveway, running, and the turtle light went out by itself. Leads me to suspect that the traction battery got too warm. However, an over-temp traction battery should set some fault code, and I didn't see one with my TechStream. Is that the usual behavior?
     
    #1 dabard051, Sep 17, 2025 at 6:50 PM
    Last edited: Sep 17, 2025 at 7:21 PM
  2. Trombone

    Trombone Active Member

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    Was car parked in the sun? With windows closed? Did turtle disappear after you drove it awhile, with A/C on?
     
    #2 Trombone, Sep 17, 2025 at 6:58 PM
  3. dabard051

    dabard051 Tinkerer-in-Charge

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    Trombone, it WAS parked in the sun, but the rear windows were open an inch. Did NOT drive with the A/C on. See my edit above for the resolution. The experience does leave me a bit nervous about this battery set performing in warm weather.

    <edit> I keep a thermometer in the car, and the internal cabin temperature was 105F. Cooled down to 90F pretty quickly as I drove with the windows open. I DID hear the traction battery fan on full while I was driving with the Turtle Mode light on (total drive excursion was about 6 miles).
     
    #3 dabard051, Sep 17, 2025 at 7:24 PM
    Last edited: Sep 17, 2025 at 7:29 PM
  4. Trombone

    Trombone Active Member

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    Advice I've read, and it makes sense to me, is to run A/C in hot weather (fairly often in FL, I suspect), as air intake for HV cooling fan is on rear shelf, and cooler cabin temp air will make the HV happier.
     
    #4 Trombone, Sep 17, 2025 at 7:44 PM
  5. VintagePrius

    VintagePrius Junior Member

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    Are you running on the original/OEM replacement/rebuilt traction battery and what mileage?
    Not sure at what point you measured the module voltages but here's what I've found…If there's a difference between module voltages greater than 0.3v (0.69 in your case) the car engages turtle mode which allows it to charge all modules over 100% i.e. perform a top balance. When it does this the traction battery fan will be at full speed because the modules will get not a little warm. This is (or was) considered quite normal behaviour for my model and probably why there's no code. However, if it has to do this on more than 3 occasions it'll likely throw up the red triangle because one (or more) modules is failing and cannot be brought back into line with the rest. That's when you will get a few codes. Depending on how serious the ECU deems it to be will determine whether or not the car will allow you to drive it any further…ask me how I know this :(
    Regards, Jay
     
    #5 VintagePrius, Sep 17, 2025 at 9:17 PM
  6. ChapmanF

    ChapmanF Senior Member

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    I have little confidence that the turtle light and top balancing are related.

    I caught my gen 1 doing a top balancing cycle several times (those posts are around here somewhere). The turtle light was not involved any of those times.

    I did see the turtle light one summer day when taking a steep twisty road at very low speed. It seemed to be a warning that the car was putting a temporary limit on battery current because of extreme battery temperature or very low charge. Pretty much as the owners' manual explains it.

    [​IMG]
     

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    #6 ChapmanF, Sep 18, 2025 at 12:09 AM
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