Alarm

    just come back from a few days away to be told that my 840 alarm had being going off all by itself with no reason.

    It seems to go off for a few seconds and then does it again about 1 hour later.

    I have now locked on key alone until one of you nice people tells me what is thye problem.

    Thanks.
    Hayden

    My alarm starting going off on its own?! Turned out to be the boot loom harness wires snapped and shorting intermittantly.Just an idea?

    Regards Trevor

    Thanks for responses chaps, but neither of those seems to be the problem.

    Research has found bonnet alarm sensor is a very common reason for this alarm triggerring on BMW models.....some people disconnect it and never replace it as they cannot see the point.

    Anyway...can someone tell me where this bonnet sensor is located.

    Thanks.

    Is it possible something like a spider \ fly \moth is inside the car and setting it off? Could try covering up the internal movement sensors.

    93 850 CSI
    hung like Einstein, clever as a horse

    Unless the spider \ fly \ moth can rock the bejeesus out of the car they won´t get noticed. Ultrasonic interior protection only from E38 onwards. What BMW called "interior protection" in the E31 was nothing more than a Hall sensor which fell down once the glass broke (and thus triggered an alarm) in combination with a liquid filled plastic box which sort of detected an out of plane condition of the car (ie lifting on a flat bed, rocking on a ferry).


    Cheers
    Reinhard

    I have what looks like 2 little micro-phones slipped into the top of the A Pillars. I always thought they were 2 little motion detectors or something. :dontknow:

    93 850 CSI
    hung like Einstein, clever as a horse

    shiggsy: Early cars had the microphone of the handsfree mobile phone in that area, although in that case there should be only one and only on the driver's side A pillar... Is your car at any chance equipped with an aftermarket alarm system?

    revtor: Got them in both pillars. It used to have an aftermarket system but the previous owner disabled it as it kept locking him out of the car. I thought they were OEM, I'll have to trace them see where they go. 11 years of ownership and still finding things out about it. :laugh:

    93 850 CSI
    hung like Einstein, clever as a horse

    Suddenly bahaving itself about 1 day after I first reported the problem.

    Took it to BMW but no trace of errors in diagnosis equipment....strange :dontknow:.

    Been perfect for 2 weeks or so, but suddenly did it again this afternoon.

    Any ideas lads ???

    Car sitting on yard at front of my garage showing 18 degrees ext temp....leads me to wonder if temp can cause trigger of alarm ???

    Zitat von koenig dave;100185

    If you still have the OE factory fitted alarm, it has a built in battery.
    they can fail.
    Time to update!



    Alarm problem back again after long time behaving itself.


    Do you know where I can find the unit that contains the battery and what sort it is on my 840.


    Cheers.
    Hayden

    Was the car in the sun when the alarm went off?


    The inclination sensor in the boot has been a suspect fairly often in the past when the alarm goes off for exactly no reason. In one of my cars this is triggered by heat, e.g. boot heating up in the full sun.


    Here is a posting with pictures and location.
    Maybe you unplug this sensor for the time being and see what happens.


    Cheers
    Reinhard


    Thanks for that Reinhard....as a matter of interest do you know what all the components and sensors are in the Alarm System and where they are located. Maybe I just then eliminate them one by one until I find the culprit.


    BMW dealership has run diagnostics and tells me that the problem lies in the wiring loom....funny that but they said the same thing when I had an ABS problem which was diagnosed by an indie as Pump problem which replacing cured. Maybe wiring harness problem is thir diagnosis for everything...you are then supposed to book it in for a whole day so they can run more extensive diagnostics at a labour rate of goodness only knows but certainly several hundred pounds.
    I don't think so !!!


    Also thanks Dave ....but where is siren and yes windows are all the way up.


    Cheers.
    Hayden

    just a quick follow-on from the last posting...


    if the car was parked with a flat rear tyre would that produce enough tilt to trigger the sensor.

    See below the DWA IV schematics showing all points of interest:


    8er.org/forum/index.php?attachment/21972/


    The inclination sensor is liquid filled and reacts upon "rocking" the car. I am sure it will not trigger the alarm when parking inclined. I have no idea how this liquid filled system works - maybe it monitors changes in resistance once the liquid starts moving. A nice place to experience the workings of this inclination sensor is a car ferry filled with 8ers :laugh:


    The alarm horn in late model cars is tucked away underneath the far end of the passenger side wiper (might be mirrored or the same location in RHD!) It is as hard to get there as it is to describe the location :roll:


    Cheers
    Reinhard


    I notice a K61 Unloader Relay in the schematic...I am intrigued that it was recommended that I should replace the 3 Unloader Relays (of which K61 is one of them) to cure my intermittent starting problems, then could the common cause of my Alarm and Starter problems be in fact a lazy K61 Relay.


    Thanks again.

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