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Thread: Power windows only work when either/both front door is open

  1. #1

    Power windows only work when either/both front door is open

    Hey guys, my power windows only work when either/both the front left or front right door switches are closed. I'm trying to diagnose the problem by referencing wiring diagrams in a manual I found but I'm not having any luck.

    The wiring diagram says that the K24 Convenience Relay (Fuse/Relay Box F1 Relay F) is what powers the Convenience Control Unit which drives the power windows. However I do not have a relay in Fuse/Relay Box F1 Relay F (The spot is empty and there are no female pins in the hole). The relay that powers my power windows is located in Fuse/Relay Box F1 Relay A which is the K5 Power Seat Relay Module. I know that because if I remove that relay, my power seats AND my power windows stop working.

    Do you guys know why my car's setup is different than the setup in the manual ? It is difficult for me to diagnose the problem if I cannot find a correct wiring diagram because I am not familiar with Mercedes-Benz.

    I appreciate your time !

  2. #2

    Re: Power windows only work when either/both front door is open

    I believe fuses G and H supply power to the power window system because power windows stop working even if either/both the front door switches are closed. Fuses G and H obviously sees 12V when either/both the front door switches are closed BUT they also see 12V when all doors are closed and the key is in accy/run/start. This means that the problem is behind the K5 Power Seat Relay Module and Fuses G/H. However I'm not sure how to continue since my wiring diagram doesn't seem to match my car.

  3. #3
    E500E Guru JC220's Avatar
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    Re: Power windows only work when either/both front door is open

    Try this wiring diagram - they are usually reliable:

    http://www.autolib.diakom.ru/CAR/Mer...GRAMS/4358.pdf
    1987 w124 200 - 3.6 AMG build | 1990 w124 300E-24 | 1992 w124 500E

    1994 320CE Sportline | 1997 w140 S280 | 2007 w211 E220CDI

  4. #4

    Re: Power windows only work when either/both front door is open

    Thanks for the wiring diagram ! It only had a small difference from the one I was looking at.

    So far I've figured out that my car doesn't have a Convenience Relay and Fuses G, H, and A which receives power from it instead receives power from the Power Seat Relay. The Power Seat Relay works properly in that it closes when either front doors are open and/or when the key is turned.

    I then checked the Convenience Control Unit's Connector A Pin 10 and Connector B Pin 6 and they both receive 12v when either front doors are open and/or when the key is turned. Because the CCU receives power under the correct conditions, I decided to stop my diagnosis and purchase another CCU to see if that fixes my Power Window problem. I will post here again after I receive it.

  5. The Following User Says Thank You to dorifuto.boi For This Useful Post:

    gsxr (4 Weeks Ago)

  6. #5

    Re: Power windows only work when either/both front door is open

    The spare CCU delivered today and I swapped it in but the same problem remains. I did some more testing and it seems like there is a relay inside the CCU that clicks when the door switch is being cycled. I have narrowed that signal down to Connector E Pin 1 because the relay in the CCU clicks even when only Connector E is connected and Pin 1 is the only signal that changes when the door switch is being cycled. However Connector E Pin 1 is not in the wiring diagram so I am at a loss on how to continue.

    I need to first find out where Connector E Pin 1 originates so that I can find out if that needs to signal as well when the doors are closed and the key is turned.

  7. The Following User Says Thank You to dorifuto.boi For This Useful Post:

    gsxr (2 Weeks Ago)

  8. #6

    Re: Power windows only work when either/both front door is open

    The problem has been fixed !!!

    I was trying to fix my other electrical problem of Fuse 1 always blowing when the key is turned. I disconnected all the things that is fed by Fuse 1 on the wiring diagram however Fuse 1 was still grounded. However I discovered that Fuse 1 also feeds the X30 distribution block. I removed the drivers side foot rest and unplugged the accessories one by one until Fuse 1 was no longer grounded. After unplugging the fourth one from the top, Fuse 1 was no longer continuous with ground, the fuse doesn't blow when I turn the key, and the windows go up and down with the doors closed and the key turned !!!

    I do not know what I unplugged and I do not know how I am going to find out. I will think about this tonight and see if I can come up with an efficient way to figure out what I unplugged.

    As a note, one of the CCU's relays still clicks when the door switch is cycled but no relays click inside the CCU relay when the ignition switch is cycled and the door is closed. Connector E Pin 1 still only changes signal when the door switch is cycled but not when the doors are closed and the ignition switch is cycled. As of now, I still have no idea why the power windows did not work when the doors were closed and key was turned. I do really want to find out but I don't have the energy to pursue this. After I find out what I unplugged from the x30 distribution block, I will give this some more thought to see if I can figure out the reason.

  9. The Following 4 Users Say Thank You to dorifuto.boi For This Useful Post:

    gsxr (2 Weeks Ago), JC220 (2 Weeks Ago), Klink (2 Weeks Ago), Melville (2 Weeks Ago)

  10. #7
    .036 Hoonigan™
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    Re: Power windows only work when either/both front door is open

    Congrats on the fix! I am curious what item #4 turns out to be. Photo attached for folks who may not be familiar with X30.

    Attached Images Attached Images
    Dave M.
    1997 E420 (Bugeyes)
    1994 E420 (Blondie)
    1994 E500 (Q-ship)
    1992 500E (Mach 5)
    1987 300D (Sportline Stage 2)
    Click here for my website
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  11. The Following 3 Users Say Thank You to gsxr For This Useful Post:

    a777fan (2 Weeks Ago), dorifuto.boi (2 Weeks Ago), Klink (2 Weeks Ago)

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