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R129 SL320 Alarm Woes

Discussion in 'Electrics, Vacuum, Ignition and ECU' started by max_gain, Jun 11, 2013.

  1. max_gain

    max_gain Active Member

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    Joined:
    Sep 13, 2012
    Location:
    Chepstow
    Your Mercedes:
    R129 SL320 1999
    Hi there

    I believe I am looking at two independent problems with my factory fitted alarm on the SL.

    Firstly, when the soft top is down and the car locked (either by using the remote key or the car auto locking itself) the alarm keeps going off. I unlock the car using the remote fob and re-lock it but after around thirty seconds the alarm goes off again. I believe the cockpit alarm is suppose to be disabled with the top down but this doesn't seem to be the case on mine.

    Secondly, with the car secured and soft top up the alarm just went off all of a sudden. I reset it using the key fob and as I walked inside it went off again. I then went through opening and closing all the doors/bonnet and boot, making sure the windows were all up and ensuring there were no spiders or anything around the ultra sonic sensors. Eventually as it was late at night I had to disconnect the battery.

    With all the problems I am having with this alarm I am wondering if there is any way of disabling it permanently. I notice there is a fuse in the boot that relates to the ATA module. Will removing this disable just the alarm only or will it cause problems with the central locking and immobiliser.


    Any help would be most appreciated

    Kind regards

    Stu
     
  2. OP
    max_gain

    max_gain Active Member

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    Joined:
    Sep 13, 2012
    Location:
    Chepstow
    Your Mercedes:
    R129 SL320 1999
    Alarm update

    Today I reconnected the battery and removed the fuse in the boot and the alarm still worked. After further investigation I noticed there was also a fuse labelled ATA in the main fuse bank under the bonnet. I pulled this one also and tested the alarm by firstly tapping the soft top and then manually opening the drivers door which normally sets the alarm off. The alarm now appears to be deactivated. Also the car starts OK which is good, so I am still able to use it. The only thing different is there is now an audible bleeping sound coming from the passengers foot well when the key is turned inside the ignition to position two and when the car is started which lasts about twenty seconds. It does appear that these alarms are problematic as others have also replaced them.

    Anyway I am happy with this resolution at present as its not constantly going off and annoying my neighbours. I will probably look to get an aftermarket alarm like many others have.
     
  3. germanmerc111

    germanmerc111 New Member

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    Joined:
    Feb 15, 2011
    Location:
    Cambridgeshire
    Your Mercedes:
    SL500
    Have a similar Problem, except my Alarm starts while driving down the Road.I did notice everytime this happens the Bulb Fail light on Dash comes on.I have to get out of the Car to lock Car to stop this painfull noise.
    can anyone give me a clue?
     
  4. television

    television Always remembered RIP

    Messages:
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    Joined:
    Mar 14, 2005
    Location:
    Daventry
    Your Mercedes:
    2002 SL500, 216 CL500, all fully loaded
    Not easy at all, what year is the car. Most of these problems are within the alarm siren
     
  5. W140-Spares

    W140-Spares Forum Supporter Authorised Forum Supporter

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    Joined:
    Jan 17, 2006
    Location:
    Kent
    Your Mercedes:
    R129 SL500
    I agree with Malcolm...battery leaks cause shorts within the unit
     
  6. Bibi Stein

    Bibi Stein New Registration

    Messages:
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    Joined:
    Sep 12, 2018
    Your Mercedes:
    SL320 R129
    Hi Stu, I have exactly the same problem recently, someone suggested that the alarm unit has a small battery inside it which after time it needs to be replaced. Thats why when the main battery is disconnected, the alarm starts to sound. Which exactly what happened to me as I did to preserve the charge after a lengthy lay off, that must have drained the "Alarm Battery". I am unable to locate the unit, thats what led me to this site tying to find whare it is. I shall try and remove the ATA fuse see if that works. Thanks in advance!!
    B
     
  7. mioba

    mioba Senior Member

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    Joined:
    Feb 19, 2006
    Location:
    Nottingham
    Your Mercedes:
    W124/1994/E200, W220/2004/S320CDI, W205/2016/C200, W447/2017/3.0 CDI
    I would doubt it would be simple as a fuse otherwise those inclined to steal cars would have a field day. Alarm issues like this and based on the years model of the OP it would be indicative of the horn/siren failing which is common.

    They are located usually under one of the front arches, wheel off, panelling off job to replace. The siren is easy enough to replace and its covered here a lot.

    I have researched this as sometimes (very infrequently) when I lock my car the indicators rapidly flash and this is the circuitry, battery in the siren failing.

    I don't think you can replace the battery itself as its in the siren which is sealed.

    new one from MB is the only route.

    let us know how you get on.
     
  8. Wearsafoxhat

    Wearsafoxhat Senior Member

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    Joined:
    Aug 9, 2011
    Location:
    Sunny Hampshire by the sea
    Your Mercedes:
    05 E55k Est, 99 SL500, A200
    The later 129's have the alarm unit in the engine bay behind the fuse box, drivers side iirc. Think it is a sealed unit but less than £100 from MB.
    Had a problem with my alarm going off or doors re opening. Turned out to be the key, new set of batteries and all well.


    Sent from my iPad using Tapatalk
     

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