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Thread: Air Conditioning Module short and top not working how are they related???

  1. #1
    Join Date
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    2004 BMW Z4 E85

    Air Conditioning Module short and top not working how are they related???

    New here to the BMW forum and need some help with the wifes latest purchase 04 z4. The convertible top stopped working and has been diagnosed as a short in the a/c head unit or module? is there any wiring relation of this to the top operation?
    a/c works but did seem to be not as cold.
    fuses for top are good in box, power top switch has no lights ,noise or anything. does power go thru the ac module first to this system? Also noted seat heater switches next to top switches not working. the DSC switch will illuminate the dash indicator.
    Anyone run into this? not the usual motor issues i was expecting to find.
    thanks for any help look forward to the forum here!

  2. #2
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    2001 525it
    Seems like an odd diagnosis, who did it

  3. #3
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    Exactly. Car was 1 day off the used car lot (as is law here in CA) so went back to them, he has a "specialist" who diagnosed it. which is why im fact checking it. Seems to me more of a top module or gem. I was a GM tech for years but we had 1 computer in our shitty cars! Hoping someone had something related here!
    Glad he offered to look at it for free.

  4. #4
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    2008 Z4
    Would need to find electrical diagram/map to trace issues to see if indeed realted or separate.
    Did any codes come up?

  5. #5
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    I would take it to a good bmw independent shop for dx

  6. #6
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    2004 Z4R 06&12 Cooper S
    Kbus
    https://www.bmwgm5.com/bmwgm5/K-Bus_Troubleshooting.htm
    Just went through this with several electrical gremlins.
    All it takes is one bad module and all are affected. Isolate the bad ground and all should come back online.
    Worked for me.
    Last edited by dbarton62; 07-29-2018 at 07:31 PM.
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  7. #7
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    you da man!

    Quote Originally Posted by dbarton62 View Post
    Kbus
    https://www.bmwgm5.com/bmwgm5/K-Bus_Troubleshooting.htm
    Just went through this with several electrical gremlins.
    All it takes is one bad module and all are affected. Isolate the bad ground and all should come back online.
    Worked for me.
    Thanks, THIS is what forums are for, you rock! -Monday the seller is having his guys put in a a/c module he got used locally.
    The k bus is the only link to anything from what i see. (found some schematics https://www.newtis.info ) Il take the car from there if that's not it i guess.
    and yes turn signal indicators did stop working before dropping it off.
    Il find out codes and what his diagnosis guy did tomorrow.
    Im thinking check the battery health first, was sitting on a used car lot after all. maybe disconnect,remove, charge and that will clear everything right? Read somewhere about touching the pos and neg cables together to clear something too.

  8. #8
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    2004 BMW Z4 E85

    Back from proper diagnosis

    Just picked the car up from proper diagnosis at a independent BMW shop here in LA. After several days checking the k-bus system ,trying a cluster and power distribution box as these were all related to codes set, it was found the airbag module is bad causing all these problems.( no top operation, a/c/ warm,cluster lights, turn signal indicators,steering wheel radio controls etc..) Car has clean title and car fax but i noticed some front end damage, new bumper cover, core support tweaked, and body lines suck.
    So i think the used dealer is 100% responsible to cover cost of airbag system by law. I myself just found the passenger seat belt crash tensioner to be deployed too.
    Clearly this thing was in a unreported crash,not fixed properly and probably missing air bags all together! Module is disconnected now and no airbag light on the dash at all.... il keep ya updated and hope not to go to court on this thing.

  9. #9
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    IMG_7856.JPGIMG_7858.JPGAnd its fixed! after shop number two who installed used airbag module and two seat belts everything in the car works. However airbag bulb itself is missing ,taped,or blown to be determined at a later date.( id rather just have the car for more than 2 days) Module was wet, corroded and shorted. 1 seat belt deployed the other high resistance.
    Note to self and others: used car lots are the worst, know the laws before you buy, and never let the wife do anything with cash in hand!

  10. #10
    Join Date
    Feb 2013
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    FL
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    2007 BMW Z4 E85 3.0 SI
    FYI this airbag control unit is known for getting corroded by exposure to water. This occurs most commonly when it accidentally rains while the soft top is down (open) as the unit is located in the center console (right behind the handbrake). Water damage causes a short circuit to happen in the K-bus system which manifests in other multiple unrelated system failures. This might explain why the control module was found wet. If it was defective from a crash the airbag light would have stayed ON since a prior crash history can’t be reset from the control module’s memory and requires unit replacement.
    Last edited by tekoo; 09-25-2018 at 02:13 AM.

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