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  1. #1
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    Unhappy No A/C, "aux fan relay" code, aux. cooling fan doesn't run

    Hi guys.
    My wife's '03 3.0i E53 a/c quit working the other day. I figured it had a slow freon leak, so I bought a couple cans of freon and stuck the gauge on and immediately got a very high reading, around 100psi. I also noticed the a/c compressor is running... It was dark and late at night, so I just went in an started trying to research on bimmerforums. Next day I hooked up my Bavarian Technic tool and found it has a "aux fan relay" fault code that reoccurs as soon as I clear it, and the auxiliary cooling fan in front of the radiator isn't switching on.
    So, I ordered a new fan and installed it today, and it still doesn't work, still has the same fault code.
    I found the 50amp fuse in the glovebox fuse panel and checked it and it's good.
    When I was initially researching this I thought I read that the E53's don't have a aux fan relay, that they just have the fuse. Is that true?
    I'm hoping there really is a relay and that it will be something simple like that...
    Anyone have any ideas???

  2. #2
    Pelican Parts's Avatar
    Pelican Parts is offline Senior Member Supporting Vendor
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    Check out the below tech article from our site, it should help you troubleshoot the aux replacement. If you have any additional questions, feel free to post a Comment just below the article and someone will get back to you with more details. Best of luck!

    Auxiliary Cooling Fan Replacement


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  3. #3
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    Mar 2013
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    I think the key to this might be that the pressure in the A/C is too high, and the refrigerant pressure sensor is sensing that high pressure and not kicking on the fan? I am not sure if the high a/c pressure is why the fan isn't running, or the fan not running is keeping the compressor from working correctly which is causing the high pressure... The compressor clutch definitely spins when you turn on the hvac system in the car, and does not spin if you completely turn off the hvac...

  4. #4
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    So I hooked up my a/c manifold to the car with "max" a/c set on the hvac panel, center of the compressor is spinning (should mean its engaged) and got about 101psi on the low side and 112psi on the high side. I think something inside the compressor has let go but I was hoping to see if anyone else agrees/disagrees before I spend $$ on a new compressor??? Thanks!

  5. #5
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    I thought the dme triggered the aux fan

  6. #6
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    2011 BMW X5 Xdrive50i
    I don't think you understand how an a/c system and an electric cooling fan works. When your a/c compressor is on, the pressure will build on the high side, once the pressure hits a specific point, your fan should cycle on. The airflow across the fan brings colder air across your condenser that in turns decreases system pressure, and your a/c system will begin to cool.

    Now if you are coding for an aux fan relay, you either have a bad relay, or bad wiring to the relay or outputting from the relay. This may be on the control side of the relay, or the switched side of the relay. Do you have a relay tester? you can test for a bad relay with one of those, or cycle it manually off the vehicle. You have to do some wire checking here then come back to us.

    This being said, I have no idea how the BMW systems control the fan and a/c system. This is just a general explanation of how a general a/c and electric cooling fan system should work.

  7. #7
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    15 650ix GC & 14 X5 50i
    The M54/m52tu/m62tu engine's variable speed aux fan turns on when a PWM signal is sent from the ECM/DME...not a relay like on the previous 2 & 3 stage aux fan found on the m62/m52 engines:




    Last edited by Qsilver7; 02-25-2017 at 11:28 PM.
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  8. #8
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    Dme I told you

  9. #9
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    2011 BMW X5 Xdrive50i
    Could be a wiring problem between the DME and the fan.

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