How to test /trigger HV battery fan

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Victorio Mo, May 27, 2026 at 9:30 PM.

  1. Victorio Mo

    Victorio Mo Member

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    I just cleaned my fan and want to test it, it's kind hard to hear it, I learned that there are 3 speeds for fan,
    Right now I start driving with outside temp and on the peak have 104-107F with outside temperature 85.

    Is this good indication that fan is working ?
    Or maybe I can try to see if any flow inside vent, with smoke ?

    Best
    V
     
    #1 Victorio Mo, May 27, 2026 at 9:30 PM
    Last edited: May 27, 2026 at 10:46 PM
  2. PriusCamper

    PriusCamper Senior Member

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    It's two wires and fan will spin if you hook those up to 12volts, or even 6 volts. Alternatively you can use Hybrid assistant app via a $20 OBD2 code reader.
     
    #2 PriusCamper, May 27, 2026 at 9:39 PM
  3. Victorio Mo

    Victorio Mo Member

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    Thanks PriusCamper,
    this is too simple test, I tested fan after cleaning on my lab power supply, it's working .
    But when you hook it into the car, it wont' run all the time, need bright temp higher, and then it's still hard to see/hear anything.

    Can you trigger fan from Hybrid Assistant? or it's the same like Dr.Prius
    I think FAN icon will be active when fan will start: This is i spic from Hybrid Assistant
    upload_2026-5-27_23-0-16.png
    Do you think it should run when PriusDoctor shows 105F?

    V
     
    #3 Victorio Mo, May 27, 2026 at 10:49 PM
    Last edited: May 28, 2026 at 2:00 AM
  4. Brian1954

    Brian1954 Senior Member

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    An easy way to test if the hybrid battery cooling fan is running is to use a tissue or piece of paper and place it on the intake vent. If the paper or tissue is sucked towards the intake, the fan is working.

    FYI, the fan can run at 6 different speeds. It is very difficult to hear the fan running at speeds 1 to 3.
     
    #4 Brian1954, May 27, 2026 at 11:01 PM
    Victorio Mo likes this.
  5. Victorio Mo

    Victorio Mo Member

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    Thanks Brian !
     
    #5 Victorio Mo, May 27, 2026 at 11:34 PM
  6. Tombukt2

    Tombukt2 Senior Member

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    I can almost guarantee you the fan is running if the plug that's the issue has been dealt with . If driving car stop like getting gas leave car ready listening ears on vent Intake . You'll hear faintly a fan motor . If it's hot enough ya really hear it . . Can you make more flow and colder probably so . Will it do much for you ? Probably not a whole lot . All the new stuff today is now using Freon various gases coolant and so on to actually cool things not just air.. air worked well until it do not.
     
    #6 Tombukt2, May 28, 2026 at 9:37 AM
  7. mr_guy_mann

    mr_guy_mann Senior Member

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    If there is an electrical fault with the battery fan then the ecu will set a fault code and turn on many warning lights - but only when the ecu tries to turn on the fan.
    I know I can't hear the fan below 125° (speed 3), so I assume speed 1 should happen by 105-110?

    Posted via the PriusChat mobile app.
     
    #7 mr_guy_mann, May 28, 2026 at 12:53 PM
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