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Thread: Auxiliary Fan constantly on high speed - E46 M3

  1. #1
    Join Date
    Dec 2019
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    Missouri
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    2002 BMW M3

    Auxiliary Fan constantly on high speed - E46 M3

    Hello. Posting my first thread so sorry if its not the best. I have a 2002 BMW M3 6spd coupe. Recently i noticed my Auxiliary fan constantly is on max speed no matter what the case is. I start the car and I can hear the aux fan getting to speed and once it gets to max speed it stays there. Its extremely loud. I replaced the bottom radiator hose sensor so I know that's not the issue. Turning the ac on or off doesn't affect the fans speed. When i shut the car off is the only time the fan turns off. Any recommendations or suggestion? My next step will probably be to replace the fan module that is connected to the fan if i can find one online.

  2. #2
    Join Date
    Jan 2005
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    Japan
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    11/88 E32 750iL+98 E36M3
    Probably the high speed fan relay is defective. I will move the thread to the E46 M3 forum
    Shogun tricks and tips for the E32 series are HERE!

  3. #3
    Join Date
    Dec 2019
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    2002 BMW M3
    Do you know where that relay is located? Thanks for responding.

  4. #4
    Join Date
    Dec 2019
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    Missouri
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    2002 BMW M3
    Any suggestions?

  5. #5
    Join Date
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    03M3 17M540 18A5SB

    I don't think there is a relay...controlled by pulse width module

    Quote Originally Posted by Dvd1371 View Post
    Any suggestions?

    https://blog.bavauto.com/14421/bmw-a...nosing-how-to/.

    You should be able to search for the module location and/or testing protocol online. YouTube probably has a video.
    Also, the E46 M3 has an engine-driven cooling fan with a viscous drive element...don't overlook a failed viscous drive element that is letting the radiator/engine run hot so that the aux fan is doing much more work than it should.

    One way of testing the viscous drive element is to start the car cold and listen to the fan as the engine warms up, The fan should roar at startup indicating it is engaged, quiet down within a minute or so indicating disengage, and then roar again when engine/radiator gets hot. Similarly, the fan should not spin really easily when cold and should be harder to spin when hot, but this requires some experience with a known good drive element.

    I've had to replace an aux fan module and an engine driven fan viscous drive element once on my 2003 drive module.

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