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Audi A4/B6 Alarm Siren - Replace NiMH Batteries

Discussion in 'General Technical / How To' started by Woorlord, Feb 25, 2010.

  1. Woorlord
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    Woorlord shifting to Hyperspace... .

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    The standard Audi B6 Siren (2001+) suffers from internal batteries becoming flat / leaking and they are not user replaceable requiring a new siren at a cost of at least £85+. The internal batteries are 2x large button cell type: "N3H 3.6v 160mAh", and are no longer made by the OEM in Germany. There are no same size equivalents!

    My solution shows how to modify the current siren unit to accommodate 6x "AA" size Ni-MH 1.2v 2000mAh batteries.

    Parts Used:
    Maplin LH21X @ £3.29
    Box dimensions: Internal 97 x 73 x 39 mm, External 100 x 76 x41 mm
    http://www.maplin.co.uk/Module.aspx?ModuleNo=1676

    Batteries: 6x 1.2V Ni-MH "AA" Cells: Maplin N04BW (Pack of 4) requires 2 packs @ £7.99 each
    http://www.maplin.co.uk/Module.aspx?ModuleNo=45787

    Battery Holder: AA x 6, Maplin HQ01B @ £0.89
    Dimensions: 58 x 44 x 28mm .....above box will accommodate this.
    http://www.maplin.co.uk/Module.aspx?ModuleNo=31427

    Battery Connector: Maplin NE19V @ £0.59
    http://www.maplin.co.uk/Module.aspx?ModuleNo=31743

    Parts Total: £20.75 + P&P (with 2 spare batteries left over!)
    excluding optional security screws, bathroom sealant & Araldite.
    Procedure:

    1. & 2. The siren unit removed from the car - in the saloon on an A4/B6 it is located at right rear corner in boot behind upholstered internal cover (pic.14). Carefully cut the siren unit open along the welded seam with a mini-hacksaw.
    3. Shows Siren in two halves

    [​IMG]This image has been resized. Click this bar to view the full image. The original image is sized 960x240.[​IMG]


    4. Label the existing terminals with a marker pen - avoids incorrect connection of new batteries, later on.
    5. The "old" batteries are held in the lid by a two cell holder. Pull this welded plastic holder out with a pair of pliers and discard.
    6. The new components obtained from Maplins are:
    • 6x Ni-MH "AA" cells 1.2v / 2000mAh
    • 1x 6-AA cell battery holder
    • 1x ABS Box
    • 1x PP3 style battery clip

    [​IMG]This image has been resized. Click this bar to view the full image. The original image is sized 960x240.[​IMG]


    7. & 8. Bolt "new" battery box to siren lid. I used 4x M4 screws / nuts / washers. I also used bathroom silicon sealant between the two plastic boxes, although this unit should not get wet.


    [​IMG]This image has been resized. Click this bar to view the full image. The original image is sized 640x240.[​IMG]


    9. Shows battery clip in "new" battery compartment through small hole drilled between the centre two fixing bolts.
    10. Shows other end of battery clip wires soldered to siren unit battery terminals. (Old Spring contacts were cut off with side cutters)


    [​IMG]This image has been resized. Click this bar to view the full image. The original image is sized 640x240.[​IMG]


    11. New batteries mounted in battery cell holder and small piece of cardboard used as packing to prevent battery movement.
    12. "New" battery compartment with lid fixed with M4 security screws for added security.


    [​IMG]This image has been resized. Click this bar to view the full image. The original image is sized 640x240.[​IMG]


    13. For test purposes I taped the two halves together and tested in car. Once I was happy all was working after "testing" -see below, I glued the two halves back together with Araldite Epoxy Resin Glue.
    14. The modified siren back in the car - you may need to very slightly bend the mounting arm.


    [​IMG]This image has been resized. Click this bar to view the full image. The original image is sized 640x240.[​IMG]


    Testing:


    a. Mount and reconnect the siren in the car
    b. Leave the siren connected in the car for ~24 hours - this ensures the new batteries are fully charged. (You could always pre-charge them if you have a suitable charger for the AA cells.)
    c. Arm your car alarm - with your windows open - leave the system for a few minutes - move your arms inside the car to activate the Ultrasonic interior sensor - Alarm should sound. Disarm the alarm - siren should stop. Close the windows.
    d. Pop the bonnet - Arm the alarm - after a couple of minutes disconnect the -ve side of the car battery. Within 5 seconds the siren should sound for ~30 secs. and re-arm itself - if the battery is still disconnected it will sound for ~30secs again, and so on. Reconnect the battery and the Siren should cease.

    If the batteries should fail in the future you can easily replace them for standard AA rechargeable ones without the need to cut open the siren unit again.
    NOTE: The batteries used here are significantly higher in capacity, 160mAh "old" vs 2000mAh "new" so should offer better backup performance for much longer if necessary ~12x longer.


    That's it all done.
    [​IMG]
    #1
  2. Chrisavant
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    Chrisavant Member

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    Brilliant solution! Thanks very much to Woorlord and QuattroJames for their help in providing this excellent and apparently fairly straightforward mod. I assume the beeping which appears to occur randomly at present is a built in warning for standby battery imminent failure? Presumably without some standby voltage present, eventually the unit would beep all the time? I ask, because I am actually not too concerned about the possibility of a thief attempting to steal my car by opening the bonnet and disconnecting the main battery, so dispensing with this feature might also be a possibility for me. But I don't want the random beeping bursts! Again many thanks. Chrisavant
    #2
  3. freddie 5
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    freddie 5 New Member

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    is this the same type of alarm that is located in the 1998 avant a4, and where will it be located....thanks
    #3
  4. Woorlord
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    Woorlord shifting to Hyperspace... .

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    This alarm unit is used on "GB" model B5's designated in ETKA (illustration 951-40) by "8D-X-200 001 >>", so assume this is from this VIN number up.
    The part number is the same, i.e. 8L0 951 605 A. VIN numbers before this and non-GB models would seem to use a "High Tone" horn and no siren.
    The other parts of the alarm system are totally different.

    ETKA suggests the alarm siren is somewhere at the back of the car - it does not show exactly where, but based on the mounting bracket it looks in a similar position to the B6 in the o/s rear quarter.
    #4
  5. AlexGSi2000
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    AlexGSi2000 Well-Known Member

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    This is excellent - many thanks woodlord.

    My siren is dead on my A4 Avant - latest price for a replacement is £108.58!

    Just ordered all the bits from Maplin so hopefully will be here in the next few days, will let you know how I get on.
    #5
  6. AlexGSi2000
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    AlexGSi2000 Well-Known Member

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    In regards to my above post - things turned out to be abit of a fail.

    Im not sure how long the alarm siren was dead for before I purchased the car, but when I opened up the siren one of the batteries had leaked all over the PCB rendering it pretty much useless (it had corroded the tracks)

    I ended up calling it a write off and purchasing one from a breakers for £20 - its the newer version, but once that dies Ill carry out the mod!
    #6
  7. hashertu
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    hashertu New Member

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    My post is intended to continue the discussion about siren failures. Apologies for the formatting but I not familiar with posting here.

    A4 (B6) Cabriolet 2006


    Fault: alarm siren makes a squeaky/rattling sound at low volume when the alarm is activated.


    The siren module is located is located in the boot (trunk) on RHS behind a trim cover.


    Access in the cabriolet is quite easy. Partially open the soft top as shown in the photo.


    [​IMG][​IMG]


    The trim is secured by a few plastic rivets. Pull out the centre pin of the rivet first followed by the rivet body. Undo one plastic nut (10mm) and remove metal part (hood rest?).


    Pull the trim away from the side bodywork at its front edge near to the hood hinge mechanism. It is not necessary to completely remove the trim as this would require the gas strut to be disconnected.


    Undo the nut (13mm) holding the siren module to a metal bracket. Pull the siren out enough that you can disconnect cable and 3 pole connector. The module part number is 8L0 951 605A.

    [​IMG]

    Using a junior hacksaw carefully cut along the plastic weld line joining front and rear casings.
    [​IMG]
    Push back the 4 edge tabs securing the pcb and lift it out.
    [​IMG]
    [​IMG]Disconnect the 2 pole connector.
    The rechargeable battery pack in this siren version are mounted on the pcb and have a higher capacity than earlier versions. The batteries were in good condition and fully charged (approx 7.8v).
    The problem lay with the siren itself.
    The sound transducer is a piezo electric diaphragm driven by electronics on the pcb.

    http://en.wikipedia.org/wiki/Piezo_tweeter#Piezo_tweeter

    The diaphragm rests on a silicone rubber O-ring and is clamped in place by the circular plastic part shown above. This part is designed to be easy to fit, not take apart. There are approximately 8 tapered tags that lock into slots in the outer casing. I don’t know if there is an elegant way to get the cover off. I machined the webs on the tabs using a Dremel tool and router bit. Alternatively use a screwdriver to gently lever the cover up while pushing the case ring outwards.
    The cover and diaphragm once removed look like this.

    [​IMG]
    [​IMG]
    The diaphragm behaves like a capacitor electrically (the specifications quote resonant impedance at 1.2kHz (say)) so you cannot use a DVM to measure resistance/continuity.


    I found the cause of the problem by accident when the pink lead pulled out of the flexible sealant supporting the lead attachment to the piezo crystal in the centre of the diaphragm.
    From what I could tell, the lead is soldered to the metallized plate on top of the crystal and then a flexible sealant poured over to provide mechanical support.


    The plating on the crystal had fractured all around the soldered joint. Whether this was simply mechanical fatiguing due to diaphragm movement or solder induced fracturing I do not know. Given that the siren has hardly ever been operated I suspect the latter. Whatever, I think it is a pretty crappy join and needs more thought given to it (thicker plating or relocate the lead connection to a point that does not move).


    My fix was to remake the soldered joint and use silicone bath sealant to support the join. The siren then worked fine again. Take care to apply the minimum amount of heat needed to get solder flow.


    Reassembly is the converse of the above.


    I used slow setting Araldite to bond the diaphragm cover back in place. Then more araldite (because of its gap filling properties) to join the two parts of the siren cover back together again.


    How long it will last is anyone’s guess.
    #7
  8. ed b
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    ed b New Member

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    Also don't make the mistake of trying to test with 12v on the pins as I did yesterday and today I opened it up and realised I have fryed two components
    #8
  9. andy.l
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    andy.l Member

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    Excellent write up,my alarm is making the 4 beeps at the moment so hopefully caught it before the batteries leak,shall be attempting this mod myself,thanks again :thumbsup:
    #9
  10. andy.l
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    andy.l Member

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    Bought the bits and followed the instructions, success of a sort.

    the siren sounds when it's armed and either door, boot opened but it will not sense any motion inside the cab if I leave the windows open and wave arms inside after 30 secs??

    am I doing something wrong?
    #10
  11. S4_dan
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    S4_dan Fire up the Quattro!

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    Scan the car with VCDS to see if any faults logged within the alarm system.
    Or check that the switches that temporarily disable the internal sensors are not stuck on. Usually found inside the drivers door pocket towards the rear.

    Dan
    #11
  12. Kitkat
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    Kitkat New Member

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    Can anyone tell me where the alarm sounder can be found on my A4 2002 (B6) Avant?
    I've searched, but only ones that mention where it's mounted is for the saloon models.

    Kit
    #12
  13. quattrojames
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    quattrojames Moderator Staff Member Moderator

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    It's on the offside, accessed through the boot hatch by the rear light. You'll need to take the trim out and remove the amp to get the siren out.
    #13
  14. Kitkat
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    Kitkat New Member

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    Cool, found it now. Thanks.
    #14
  15. andy.l
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    andy.l Member

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    As James has said, remove boot spare wheel floor, right had side plastics and the bass speaker box, it's then held in with 1 nut down under the rear light cluster, it's a pain but manageable :)
    #15
  16. benjie
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    benjie Active Member

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    Did this today - thanks for the write-up Woorlord!
    #16
  17. AceOn Group
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    AceOn Group New Member

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  18. Chatis
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    Chatis New Member

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    I got a new alarm sounder form the stealer ship since the old one was fubar. Put it in and thought the problem was over. Not quite! It's going off again. Now it will stop if I unlock the doors but if I lock it off it goes. Any ideas now.
    #18
  19. Woorlord
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    Woorlord shifting to Hyperspace... .

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    Scan your car with VCDS - it will tell you exactly what has set the alarm off. You may have a faulty switch in one of your doors - had problems previously with VW Passats with tailgate alarm switches in locks.
    #19
  20. kmantripp
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    kmantripp New Member

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    I had a corroded PCB in my 2001 TT alarm siren caused by battery failure, after replacing this with a new unit still no alarm sound on triggering an alarm condition. I had to replace both the siren and the alarm control module, possibly the siren fault had taken out the control module.
    #20

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