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Thread: Alarm Sensor Locations

  1. #1
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    Alarm Sensor Locations

    Is there a good diagram or writeup on here regarding the alarm sensor locations? I seem to be having an issue with my factory alarm, and I would like to trace the problem by disconnecting sensors until I figure out which is bad.

    I'm looking for the ultrasonic sensor, hood sensor, and motion sensor.

    Any other thoughts or ideas would be appreciated.



    Issue:
    Car will start and run fine, I'll shut it off, and immediately try to turn it back on, nothing. Alarm goes off for no reason, and I'm getting a battery drain as well (haven't traced the circuit for the battery drain). The electrical problems with these cars are maddening. If I disconnect the battery for 5-10 minutes, it will start again. It's not every time I shut the car off, but I would say it happens about 60-80% of the time. Battery tests fine, all electronics work great, strong blower motor, bright lights, loud radio, etc., just dead key. I don't think the issue is related to the battery in the key or chip key reader. It seems alarm related. (or possibly a bad starter, but that shouldn't correct itself by resetting the battery)

    - Will

  2. #2
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    In a sedan or coupe the ultra sonic sensor is in the ceiling. It's shaped like a bow tie. It can tell if someone reaches into the car through an open window. There is a tilt sensor in the trunk. It's located on one of the rear quarter panels. It should be a small square white box. It senses if someone jacks up the car to crawl under it or steal your wheels. The hood uses a switch. Can't remember if it's around the radiator or near one of the hinges. It's easy to see.

  3. #3
    dworthy's Avatar
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    Well there is actually 2 sensors:
    Ultrasonic/Motion sensor
    Tilt Sensor

    There is also an alarm horn which has a built-in battery so in case the thief pulls the power wire off.

    So as an ASSUMPTION that you have a convertible, this is where you find them at:
    Tilt sensor - Above the battery behind the trunk liner. It will be mounted by the fuel filler neck.
    As for the Ultrasonic sensor, on the early verts, I don't know, but I think it is in the vicinity of the Hazard switch.
    The hood switch is locked in the drug bin, or on the euro cars, battery compartment. Also it will be on the other side of the Positive jump connector.
    As for the Horn, it will be located on the right side of the car, behind the cabin air filter. You will need to remove the cabin filter and the bracket to be able to see it.
    Darin
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  4. #4
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    Yup, 330 CI, convertible. The ultrasonic sensor and/or motion sensor seem to be an issue (is there one sensor or two?). Would it be under the center counsel then?

    I'm going to try disabling the tilt sensor and hood sensor and see how it goes.


    Quote Originally Posted by dworthy View Post
    Well there is actually 2 sensors:
    Ultrasonic/Motion sensor
    Tilt Sensor

    There is also an alarm horn which has a built-in battery so in case the thief pulls the power wire off.

    So as an ASSUMPTION that you have a convertible, this is where you find them at:
    Tilt sensor - Above the battery behind the trunk liner. It will be mounted by the fuel filler neck.
    As for the Ultrasonic sensor, on the early verts, I don't know, but I think it is in the vicinity of the Hazard switch.
    The hood switch is locked in the drug bin, or on the euro cars, battery compartment. Also it will be on the other side of the Positive jump connector.
    As for the Horn, it will be located on the right side of the car, behind the cabin air filter. You will need to remove the cabin filter and the bracket to be able to see it.

  5. #5
    dworthy's Avatar
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    Yes I think it is, as I haven't worked on a Vert is some time, I am not 100% sure on it's location.

    Of course all the others will be in the roof behind a square box that hangs down a bit behind the sunroof.
    Darin
    Current:
    16 220i Active Tourer Platinsilver MET (C08)/Dakota Black (PDSW), P7ACA, P7LDA, P7LHA, P9BDA, 6sp Manual - Wife's new toy!
    05 325it Electric Red(438)/Gray(N6TT) ZCW, ZSP 5sp Manual Back set cover, trunk mat, Euro Infra-Rot front windshield, and mud flaps! Mr. Wagon My new Winter car.
    05 M3 Imolarot II(405)/Gray(N5TT) ZCW, ZPP 6sp Manual C.F. Lip, CSL diffuser, SSK, Euro Infra-Rot front windshield and a trunk liner! Mr. Go_Fast Stored for the Winter
    Past:
    95 318is Montreal Blue Met (297)/Beige(K1SN) RIP, killed by an Idiot.
    84 M535i gray market Burgandy Rot Met/Black Leather Lowered by Intrax on bilies, poly everywhere, B&B cat back system, K&N, and a hitch! Da Beast - Still running w/400k+!
    91 316i euro Tizianrot/Gray cloth - E-36 w/M-40 RIP, but great on gas! Best was 38 MPG
    82 528i euro Saphire Blue Met/Blue Leather RIP
    79 525 euro Green/Green RIP
    79 318 Silver/Black - The first one that got it all started
    M-Flight Member

  6. #6
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    Thank you for the replies.

    On a related note:

    I've read some responses on here that indicate that the alarm horn has a separate battery, and that battery or the horn itself has been traced to a drain of power of the vehicles main battery. What's the best way to test this?

    Also, a reply on a different thread has stated that a key programmed to the car will still start the car if the alarm is triggered. Is that correct?

  7. #7
    dworthy's Avatar
    dworthy is offline Wagon meister :) BMW Tech Expert
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    Yes there is a battery built into the Horn. If it drains while the car is off, I haven't heard of that before. Now if you have an old/weak battery, it would seem plausible, as most auto batteries last 6 years. I would think that the GM-5 would turn off the charging like everything else when the car goes to sleep mode.

    I had my wagon start with the alarm going off, and drove down the road, so yeah it is possible.
    Darin
    Current:
    16 220i Active Tourer Platinsilver MET (C08)/Dakota Black (PDSW), P7ACA, P7LDA, P7LHA, P9BDA, 6sp Manual - Wife's new toy!
    05 325it Electric Red(438)/Gray(N6TT) ZCW, ZSP 5sp Manual Back set cover, trunk mat, Euro Infra-Rot front windshield, and mud flaps! Mr. Wagon My new Winter car.
    05 M3 Imolarot II(405)/Gray(N5TT) ZCW, ZPP 6sp Manual C.F. Lip, CSL diffuser, SSK, Euro Infra-Rot front windshield and a trunk liner! Mr. Go_Fast Stored for the Winter
    Past:
    95 318is Montreal Blue Met (297)/Beige(K1SN) RIP, killed by an Idiot.
    84 M535i gray market Burgandy Rot Met/Black Leather Lowered by Intrax on bilies, poly everywhere, B&B cat back system, K&N, and a hitch! Da Beast - Still running w/400k+!
    91 316i euro Tizianrot/Gray cloth - E-36 w/M-40 RIP, but great on gas! Best was 38 MPG
    82 528i euro Saphire Blue Met/Blue Leather RIP
    79 525 euro Green/Green RIP
    79 318 Silver/Black - The first one that got it all started
    M-Flight Member

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