Replacing Your Broken Alarm Horn
 

Picked up a 2001 D2 FL a few months back and one of the niggles it had was it kept blowing one of the fuses, which also affected the interior lights. After some searching, the best possible cause was a failed alarm horn caused by leaking batteries. So I ventured, screwdriver in hand, to find the alarm and fix it. The following is how I went about it.

Remove the boot carpet by unscrewing the two plastic screws shown.

http://forum.a8parts.co.uk/picture.p...&pictureid=470

The alarm horn is located behind the trim on the left side of the car, behind the CD autochanger.

http://forum.a8parts.co.uk/picture.p...&pictureid=471

Remove the curved plastic trim at the side of the boot. There are two plastic lugs holding it in place. Pull the centre part of these out about halfway and then pull out both outer and inner parts.

http://forum.a8parts.co.uk/picture.p...&pictureid=472

This piece of trim is also secured by what I can only describe as industrial strength velcro. It is very tough indeed, so care is needed when removing it. If possible, try and ease the trim away from the car using a thin piece of wood between the trim and the car.

http://forum.a8parts.co.uk/picture.p...&pictureid=473

The next piece of trim to remove is along the back of the car. Here, you need to remove the two tie-down catches, two plastic lugs and the boot light. I think the two plastic lugs had covers (similar to others in the boot), but mine were missing. If you have them, just prise them off carefully, as they have a section that goes into the groove on the other lugs.

http://forum.a8parts.co.uk/picture.p...&pictureid=474

Now remove the boot light. Use a flathead screwdriver and gently prise it out from the end. Remove both wires.

http://forum.a8parts.co.uk/picture.p...&pictureid=475

Now remove the two tie-down catches using a Philips head screwdriver. Once removed, I tend to leave the screws in the catch for safekeeping.

http://forum.a8parts.co.uk/picture.p...&pictureid=476

It's now time to remove the trim itself. This was the one I had the most issues with, as I didn't know what else was holding it in place. Start to prise it off from the left side of the car, as the right side will still be held in place by the corresponding curved piece of trim. You may also need to prise it up ever so slightly, as mine was catching on the plastic base of the boot.

http://forum.a8parts.co.uk/picture.p...&pictureid=477

There are also four plastic clips holding the trim in place. Again, a thin piece of wood between plastic and metal for leverage is handy.

http://forum.a8parts.co.uk/picture.p...&pictureid=478

Time now to remove the CD autochanger. There are four 10mm bolts holding it in place. The one at the back right is the most awkward one to remove unless you have a knuckle joint in your socket set. Once these are removed, carefully move the unit out and back to get access to the cable. You are almost rotating it about the front right bolt.

http://forum.a8parts.co.uk/picture.p...&pictureid=479

To get better access, use needle nose pliers and squeeze the base of the plastic cable tie holding the cable in place. You should then be able to push it up out of the metal chassis. This will allow you to move the unit further into the boot area.

http://forum.a8parts.co.uk/picture.p...&pictureid=480

Final piece of trim to remove before getting to the trim is the access cover for the lights. A simple 90 degree turn and out it comes.

http://forum.a8parts.co.uk/picture.p...&pictureid=481

Strangely I didn't take a photo of the next stage, but what you now need to do is to gently pull the trim out from its position. You sort of have to take each piece of trim and draw them all together so that they don't catch on anything and then move it out and back, something like you do with the CD autochanger. The main thing is not to move it too far out as you may crease it.

If you now look up into the top recess, you will see a small black box secured by a bolt. This is the alarm horn, and the culprit. Simply undo the bolt, raise the alarm up and then pull it gently back towards you. Note that the cable is very short, so it isn't going to move far.

http://forum.a8parts.co.uk/picture.p...&pictureid=482

You should now be able to turn it around and unplug it from the loom. As you can see, the loom is very short indeed, and in my case even the plug has been corroded - so I can defintely say that the alarm is kaput.

http://forum.a8parts.co.uk/picture.p...&pictureid=483

And if you're interested, this is what the inside of the alarm looked like when I pulled it apart.

http://forum.a8parts.co.uk/picture.p...&pictureid=463

If you're lucky and the plug isn't corroded, you just need to get a replacement alarm. If it's like mine, then you either need to get a new plug (from where I don't know) as well. The alarm isn't specific to the A8, so others can be used, so long as they have the three pin plug. I was lucky to get one from a 05 A4, along with about a foot of the loom (BTW it's located in the lower right corner of the boot). Again, if you have to replace the plug, cut the cables as close to the plug as possible, as I took about ten minutes to splice the new one on. It was mostly done by feel.

The obvious next stage before putting it all back together is to test that everything works. Close the boot and lock the car with the windows open. Wait for it to arm itself and then stick your arms into the car. With luck, the indicators will flash and you will get an annoying; but comforting; noise from the back of the car. Mine doesn't beep when I lock or unlock it, but I might need to use VCDS to sort that out.

Reconstructing the boot is very simple. Just follow the same steps in reverse :)

Place the new alarm in position and secure in place with the bolt. Move the trim back into position, again being careful not to crease any of it. You may need to fiddle with it to get all of it to line up. Replace the plastic light trim cover. Move the CD autochanger back towards its original position when you first moved it out. This allows you to secure the plastic cable tie in the autochanger chassis. I marked the hole where it should go. This is more awkward to do than removing it. Once done, rotate the autochanger back into position, being careful not to trap any cables at the back of it. Again, a bit of jiggling about may be required to seat it properly. Secure all four screws in position first by hand before tightening them down.

The rear plastic trim now needs to be replaced. This is a fiddly bit, as you need to secure the right side into position with the curved right piece of trim. You also have to feed the two wires for the light through the relevant hole and then place the trim in position so that the four plastic clips are aligned to their respective holes. Holding the trim in place, start from the right side and push down on the trim above the plastic clips to secure them. You will feel them going into place.

The next part is fitting the light while you still have a hold of the wires. I'm not sure about the wiring, so wired it exactly as I took it off, brown cable at the bottom. Feed the light into place, cables first, and then push in to secure. Secure both tie-down catches and then replace the two plastic lugs. Replacing the curved plastic trim is done by aligning it into the slot with the bottom trim piece and then pressing it to the velcro. Use the palm of your hand over the four areas marked and apply pressure and you will feel it snap into place. Then take the two plastic lugs and place them in the relevant holes, and then push the centre part all the way in. You may need to jiggle the back one, as you have to align the trim and the plastic to the hole. Finally, replace the CD cover and then secure the boot carpet with the two plastic screws.

Addendum: Now that my alarm works, I wanted it to 'blip' when I locked the car. Came across a link to the following site 'Waks Wide Web', where it gives details on how to encode it with VCDS and a little downloadable program called BaseCode.

I hope you find this guide useful.

This is extremely useful. Love these articles. Thank you so very much for it.

Do you have antenna on the boot?

Based on your picture of where the recess is it seems that antenna is directly above it and what we see is water damage from poor antenna seal dripping directly on the unit.

On picture of damaged plug I also see sound deadening material of what seems to be central locking pump. Are we sure there is no water ingress there?

Agreed, great write up. Can we make it sticky please?

I also had problems with the aerial seal - but not on my current car (sorry David!) - and had to have the central locking pump replaced.

Thanks, great write up -
Added to the Interior Electrics Repair Sticky +++

Great write up, thanks for the contribution +++

No aerial at all on the car. Probably explains the c*ap reception on the radio. I pulled the alarm apart, and it was definitely caused by the two big button batteries leaking, which someone suggested.

It's in the rear window think it uses the demist wires and is why the FL rear screen looks like it's come out of the 70's and the PF is almost completely clear.

>> I pulled the alarm apart, and it was definitely caused by
>> the two big button batteries leaking, which someone suggested.

Thanks! I will open my box next time I get there and change those button batteries preventively.

My PF rear screen was equally riddled with wires as well as the "twirly" fixed aerial. But it did have the "full monty" of TV, LW/MW/FM radio, GSM and phone.

The alarm horn is a sealed unit. Since mine was kaput, it didn't matter how I pulled it apart. It you plan on replacing the batteries, you're going to need something like a dremel to cut it apart where it was stuck together.

Thanks. Will attack with a dremel ! :)

See previous thread here for links to articles about getting the unit open and battery replacement:

http://forum.a8parts.co.uk/showthrea...ght=alarm+horn

Added some info on the first post on how to get the alarm to 'blip' when locking.

Handy little program there "basecode", I just used Google to convert decimal to binary and back when I adjusted my settings.
I looked at a number of sites and found these values for the various bits, not sure what they all mean though. :tuttut:

For Central Locking (35):

+00001 - Rear Lid Opening via Rear Lid Lock
+00002 - Anti-Theft Confirmation via Blink
+00004 - Selective Locking
+00008 - Anti-Theft-System
+00016 - Reverse Lock And Unlock Functions On Remote
+00032 - Locking via Speed (15mph)
+00064 - Comfort Closing via Remote Control
+00128 - Turn Off Continuous Blinking Of Alarm LED When Anti-Theft Armed
+00256 - Rear Lid Logic
+00512 - Remote Control "Close" Confirmation (1x Blink)
+01024 - Confirmation Anti-Theft Warning System Horn Activation
+02048 - Door/Window Logic (USA)
+04096 - Remote Control "Open" Confirmation (2x Blink)
+08192 - Remote Control

Excellent work Sean +++

I used this guide to finally extract my unit - mine hasn’t worked since getting the car 2+ years ago.

All was well until I looked at the unit which is completely different. Do you think someone has replaced it with another models unit in the past or did 8’s come with these at some point?

The connections appear to be the same and the part number on eBay pulls up a handful of used units although not from out forum sponsors. Do I get the same as what I removed or go for one like Sean’s box shaped like unit instead?

Sean's from the first post is actually the later unit which was supposed to be more reliable. I'd go for the later flat one since most of the early cube-shaped modules seem to be kaput by now.

Was there a specific part number for the later ones?

All the ones I’m seeing on eBay appear to have a rectangular connector but mine is rounded at one end as shown in Sean’s second to last picture.

The one I got was from a '05 A4 and had the 3-pin rounded connector. The part number is 8L0951605A, which is identical to the part number for a '02 A8, although as MJ mentioned, the later ones are slimmer. There are a few listed on eBay for around the £30 mark.

Ah yes, I see what you mean now! Thanks pal +++

Well I managed to fit the new unit today. I’ve never had a working alarm on my 8’s so I had no idea they were so feeble sounding....it’s almost comical that a big brute of a car has such a quiet alarm.

I don’t think it would wake me out of my sleep if it was being tampered with!

I think the feebleness is down to having a common design shared across a number of VAG ranges of the same era.
They're designed, I think, to be bolted firmly to the bodywork and use the body panels as a sounding board.
That's fine with a steel chassis/body but doesn't work so well with aluminium...… :tuttut:

http://forum.a8parts.co.uk/attachmen...1&d=1535893433

:ROFL: