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Power window weirdness on our old '98 Grand Cherokee....

Discussion in 'Grand Cherokee, Durango, etc' started by LouJC, Jul 29, 2020.

  1. LouJC

    LouJC Active Member

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    Now we all know that older Jeeps are known for electrical issues but this is weird, even for them. On ours 8/10 times when we turn on the ignition, the right rear window goes down by itself. It operates properly from both the driver's master switch and the door switch, but does this by itself. Any ideas of what to check? I have heard of issues with the driver master switch.....
     
  2. AllanC

    AllanC Well-Known Member

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    To operate the right rear window from the driver side master window control, the right rear switch at driver location sends an appropriate signal command over the network bus to the PDM (passenger door module). The PDM interprets the command and activates and grounds the appropriate circuits to the right rear window motor to cause it to move up or down according to request.

    Operating the right rear window switch at the window location bypasses the PDM and provides appropriate power and ground to the right rear window motor and moves it accordingly. So this phantom operation of the power window motor has to be attributable to some strange behavior of the PDM or a stray signal to the PDM that is causing unexpected right rear window movement. Disable the rear power windows from the driver side master window switch control. Does the phantom operation of the right rear window still occur?

    The BCM (body control module) talks to the PDM and provides power to it after ignition switch OFF for window operation for a short time period. After turning OFF the ignition key switch but before opening any door is there power such that you can operate (raise and lower) the right rear power window?
     
    #2 AllanC, Jul 29, 2020
    Last edited: Jul 29, 2020
  3. AllanC

    AllanC Well-Known Member

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    I made an incorrect statement noted above. The BCM communicates via network BUS and tells the PDM when to power up and power down. It does NOT have a physical input power feed to the PDM. Subtle but necessary interpretation of the functional relationship between the modules.
     
  4. LouJC

    LouJC Active Member

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    thanks for your detailed reply! it does make sense to me that it could have to do with the PDM, because long before the ghost window action I had and still occasionally have this as a chronic intermittent problem:
    all doors and locks work normally for a period of time then:
    only the driver's side window/s work nothing else either from the master switch, or the individual door switches except the pass side front door lock switch
    then: if someone slammed the passenger door, it would all start working again
    or: if I cycled the pass side front door lock switch, it would magically start working again.
    My thought was to take off the pass side door panel and clean all the contacts with contact cleaner.

    and one last thing, we have owed this since new, and it had a major electrical issue when new. When locking the vehicle with the remote, (normal for the horn to chirp), sometimes the horn would get stuck on full blast. Took 4 attempts to fix! and they replaced the BCM, but that was not the cause, it turned out to be the horn pad arcing. The problems with the windows not working started years after they replaced the BCM though...
     
  5. AllanC

    AllanC Well-Known Member

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    Jarring movement fixes the problem. That would lead one to believe there is a contact / electrical connection issue somewhere in the system on the passenger side.

    I would imagine that when this phantom operation occurs and the right rear window lowers automatically with ignition key switch ON, you raise the right rear window and close it by activating the appropriate switch at the driver's side switch group.

    Next time this happens reach to the back and raise the right rear window by using the power window switch at the window location. Do NOT close the window with the appropriate driver side control switch. Then turn off the ignition and turn ON again. Does the phantom operation at the right rear window occur and the window automatically opens? If NO then the problem is probably sticking contacts in the power window switch or a short inside the switch at the right rear window area.

    There may be a body diagnostic code stored indicating an issue with a power window control circuit on the passenger side of the vehicle. You would need a sophisticated scan tool to interrogate the BCM and determine if this condition(s) existed. If present that would lead to evidence that there is a problem with the right rear power window switch or its circuit. Or a circuit problem could exist with the PDM in the right passenger door.
     
    #5 AllanC, Jul 30, 2020
    Last edited: Jul 30, 2020
    valiant67 likes this.
  6. LouJC

    LouJC Active Member

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    Thanks will try that and report back!
     
  7. LouJC

    LouJC Active Member

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  8. AllanC

    AllanC Well-Known Member

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    So something in the right rear window switch is causing a voltage feedback on the 2 circuit wires between the power window motor and the PDM (passenger door module). So when the ignition key switch is turned to ON / RUN position, the BCM sends a message to the PDM to power up. Stray, unexpected voltage causes the PDM to lower the right rear window. Just BIZARRE !

    It may be a mechanical problem that a thorough cleaning with electrical contract spray may fix. Or something is broken and causing an intermittent short between contacts. I would suggest replacing it and be done with the aggravation.

    RockAuto shows the rear power window switch for about $22.00. I found a Mopar part window switch on Amazon at $47.00. You have options.
     
  9. LouJC

    LouJC Active Member

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    Thanks that all makes sense, tried it again today and same thing, turn on the ignition and no phantom lowering!
     
  10. LouJC

    LouJC Active Member

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    I will pick a switch and replace the old one....
     

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