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2018 Prius coolant fan keep running while the car just start and the engine is cold

Discussion in 'Gen 4 Prius Care, Maintenance and Troubleshooting' started by Daniel 741741, Sep 5, 2024 at 3:07 PM.

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  1. Daniel 741741

    Daniel 741741 New Member

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    我的维修普锐斯,got a very low mileage,around 35mpg,I think the problem is that coolant fan keep running while car just start and the engine is cold ,I don’t have any engine light on the car
     
    #1 Daniel 741741, Sep 5, 2024 at 3:07 PM
    Last edited by a moderator: Sep 5, 2024 at 3:54 PM
  2. BiomedO1

    BiomedO1 Senior Member

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    Welcome Daniel,
    Need more information. If the AC is on, that will force the cooling fans on. Just because you don't have a CEL on, doesn't mean there isn't a problem. You may have a bad sensor that still within specifications but sending bad data to the ECU. If the sensor was totally dead, too high or too low, that would trip a CEL.
    Get the car scanned then report back...

    Good Luck.....
     
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  3. douglasjre

    douglasjre Senior Member

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    Land rovers were famous for electrical Gremlins like that. They used to keep all the relays under the driver seat where they got wet from off-writing and snow in the winter from the boats. Lucas electric for the win(y)
     
  4. Daniel 741741

    Daniel 741741 New Member

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    upload_2024-9-6_9-23-52.jpeg upload_2024-9-6_9-24-12.jpeg upload_2024-9-6_9-24-30.jpeg
    my engine is totally cold.
    Fans will keep running when I take off the coolant temperature sensor,I think sensor is good,I think the problem is on electrical system,some guys connect the wrong wires
     
  5. Daniel 741741

    Daniel 741741 New Member

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    I tested relay,they are both good.
    I cannot find anything wrong when I take off the fans wires.they look good.
     
  6. BiomedO1

    BiomedO1 Senior Member

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    While these cars has electronic gremlins, mainly in the informatics systems - the engine control system is pretty solid. If someone has been messing around with the cars wiring; you need to take it to a professional. A scan gauge isn't going to tell us how someone F**k-up the wiring harness. For all we know, the wires could be bypassing the sensors and hook to random resistors to fool the ECU.

    Sorry...

    FWIW: if this is a Ca car and a smog station see that, It's an automatic FAIL. There are certain modifications your not allow to do and you will be referred to a referee smog station. A smog technician will lose their license, if they get caught passing an obviously questionable car.
     
  7. Daniel 741741

    Daniel 741741 New Member

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    Thank you!
     
  8. AzWxGuy

    AzWxGuy Weather Guy

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    You might want to check your 12V battery health too. Low voltage can cause all sorts of ECU boot-up problems.
     
  9. BiomedO1

    BiomedO1 Senior Member

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    Was it really 94F when you scanned the car. The air intake temp is obviously wrong, 142F with the engine off??? 187F is right around the trip point for the fans to kick on. I believe it's suppose to be 190F +/- 5F.

    You battery is reading 13VDC. I don't think a Foxwell scanner is valid on a Prius. Clear all fault codes and see what happens. It can't hurt.