I Have a 2012 Skoda Fabia, 1.2 Tsi, Elegance. The alarm has started playing up – going off randomly and disturbing the neighbours / my wife’s sanity. Even going off while driving it! Did some research through the various forums and resources but eventually came across a thread where someone defined that the alarm siren should normally be replaced in a five year service.  Apparently few garages bother with it unless it plays up. I know why! The siren itself is fine but the NiMH battery is at its end of life and so the device begins to act erratically.

It was sited under the front windscreen scuttle tray. Lift the bonnet, at either side of the scuttle there is a plastic 10mm nut, remove them then pull off the forward edge rubber weather strip and gently begin to pull the scuttle away from the windscreen. When its loose you can open it up and see inside. Dead centre, just beneath the RHS wiper arm mount you’ll see the alarm siren mounting shield. It is deliberately awkward to get at. You'll’see a 13mm holding nut in the middle, remove it. It is a PITA to remove - I struggled and pulled and turned and twisted it but eventually it came free with undoing the wire clip from it with pliers and a small screwdriver. I jammed a block of wood in the scuttle opening to give me a window and a head torch was essential too. It would be much easier if I had removed the wipers and the whole scuttle but I didn’t have a small puller to get the wiper arm mounts apart.

Once out the siren is a simple plastic block in 2 parts glued/ sealed together. With some effort you can prise the two halves apart. That done, you’ll see the PCB at the bottom, rear facing. Very carefully, prise this out by pulling back the clips around its edge. It will be stiff – because the battery is tightly held in plastic splines beneath that you don’t see until it comes free.

The battery is a multi-cell purpose made PCB one with a solder tag at either end. They are no longer made. The nearest virtual equivalent I found was this:

https://cpc.farnell.com/varta/55615305060/battery-nimh-5cell-6v-150mah/dp/BT05127#

Slightly different but  good enough for the fix, unsolder the old and solder in the new and reassemble (with a little modification as the battery compartment is designed for the original battery; so cut the splines to get a fit... Use clear silicone around your glued seal to weatherproof it. Refit and all’s well again.

Removed my alarm siren today, it was relatively easy, removed the two plastic nuts holding the scuttle, didn't need to remove the forward edge rubber weather strip, the scuttle tray pulled out easily from under the windscreen and was able to view the location of the alarm siren. It is tight with the wipers still attached but I overcame this by cutting the scuttle (just the centre wiper hole) into a slot with some snips (this will be hidden when the scuttle goes back under the windscreen) You can now lift the scuttle over the centre wiper arm, this allows you to get loads of clearance under the scuttle. I next undid the three plastic nuts on the shroud covering the fan inlet and jiggled the shroud out from under the scuttle. The metal bracket that holds the alarm siren is riveted in place, remove the metal nut holding the siren and pull/bent the bracket towards the front of the car just a bit to allow the siren to be slid out from behind the bracket. Reassemble in reverse order. That's it, it took about 30 minutes. I only removed the alarm siren to check the part number before ordering a replacement. When the part arrives i reckon I can cut the time down now to about twenty minutes.

Edited 22 March, 20197 yr by bobob

Hi there I need to do this soon to my Cupra.  Same plastic nuts.   How do you remove them without breaking or did you guys get some replacements beforehand?.  Thanks.

Edited 25 March, 20197 yr by RAPTURE

On 25/03/2019 at 18:15, RAPTURE said:

Hi there I need to do this soon to my Cupra.  Same plastic nuts.   How do you remove them without breaking or did you guys get some replacements beforehand?.  Thanks.

I used a socket that's a snug fit, they are only plastic so that they don't go rusty, If you do break one replace with a suitable temporary metal nut until you can get a plastic one.

VCDS is reporting an error with my alarm that is likely due to a dead battery - additional symptom is that the red LED by the drivers door lights solid red immediately upon locking the car.

 

Thanks for the CPC link, unfortunately their web site says this is no longer stocked.

Once you have opened up the alarm siren unit, you will be able to see which battery you can use, I think, that without checking that CPC link, that you can buy a couple of batteries and repackage them together to be the same as what is fitted, just by using glue and/or insulating tape and maybe adding a short wire link or links - that was the way things seemed to be the last time I out of curiosity, looked into this.