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07 Peterbilt 386 low voltage to fan solenoid

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by Con707904, Dec 18, 2025 at 1:57 PM.

  1. Dec 18, 2025 at 1:57 PM #1
    Con707904

    Con707904 Bobtail Member

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    Apr 30, 2017
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    Hey guys, I have a '07 Peterbilt 386 with a C13 and the fan will not shut off. I have confirmed that the fan solenoid functions properly, however the power going to the fan solenoid with the key on engine running is only 2.2 volts. I disconnected the wiring harness on the engine bay side where it goes into the firewall and did not see any corrosion on the pins there, for whatever that's worth. Thanks for any help or direction
     
    Con707904, Dec 18, 2025 at 1:57 PM
    Con707904, Dec 18, 2025 at 1:57 PM
    #1
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  3. Dec 18, 2025 at 2:02 PM #2
    Star Rider

    Star Rider Road Train Member

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    A/C high pressure switch, Intake Manifold Temp switch.
    Plug it in and see what is commanding it on.
     
    Star Rider, Dec 18, 2025 at 2:02 PM
    Star Rider, Dec 18, 2025 at 2:02 PM
    #2
    BoxCarKidd and Con707904 Thank this.
  4. Dec 18, 2025 at 2:10 PM #3
    Con707904

    Con707904 Bobtail Member

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    Apr 30, 2017
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    If the ECM is telling the fan not to come on shouldn't it have zero volts at the solenoid?
     
    Con707904, Dec 18, 2025 at 2:10 PM
    Con707904, Dec 18, 2025 at 2:10 PM
    #3
  5. Dec 18, 2025 at 2:26 PM #4
    Star Rider

    Star Rider Road Train Member

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    Michigan
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    Without plugging it in you are just going to be guessing and throwing parts at it.
    Trust me on this one.
     
    Star Rider, Dec 18, 2025 at 2:26 PM
    Star Rider, Dec 18, 2025 at 2:26 PM
    #4
    Con707904 Thanks this.
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