Originally Posted by Adam2003 (Post 2867124)

I have taken a video however it won’t let me post it. But it sounds like a weak horn noise coming from the passenger side plenum drain when I’m charging my battery. I’ve disconnected it and I am now charging it. But does anyone know why it makes the noise when I connect it and charge? I’m guessing the battery is dead and I’ll need a new one, however I’m worried it may be something bigger than that.

Car has been sat for about 3 weeks.


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Originally Posted by clf (Post 2867134)

Upload a video to youtube and link to it, cannot post videos.

Should remove the battery to charge, at the very least disconnect it from the car!

I am guessing the horn is related to the alarm system. If it looks like a snail, it doesnt have a battery. If it is squared off box like 'thing' it will be a battery back up system (BBUS), which are prone to failure. (fitted if you have factoory Xenon headlights).

To test the alarm, the simplest method would be to open the bonnet, press the sensor button (rubber cone shaped at the front), then whilst holding it down, lock with the remote. Keep the sensor button held for about 15 seconds, then release. If the siren doesnt sound, and the indicators flash, it means your BBUS has failed. Since they are plentiful on eBay for around £10-15 (search BMW e46 e39 alarm EXAMPLE) and generally reliable in BMWs and Binis, I would just replace (a wiring plug and a nut if I recall).

If it is the snail type, I would still test, and assume, if it works correctly, it to be something related to fitting the charger to the car's wiring system.

Originally Posted by COLVERT (Post 2867137)

What you can hear is probably the anti-theft horn.

Guessing about your battery is not really a productive way of assessing it.
Get in on charge for a 24 hour minimum.--Leave it for a couple of hours then check the battery voltage.--You should see at least 12.4 volts which will be enough to start the engine. ( with luck that horn noise you are hearing will have vanished. )

Let us know how you get on.---:}

Joining the battery.---Positive first then negative.

Originally Posted by AndrewJames (Post 2867141)

Someone may correct me but I think some of the alarm systems have some sort of backup battery? So perhaps the car last remembers being alarmed, you've then gained entry to the car with the actual key and introduced some power to the battery resulting in the alarm?

To stop the horn sound I would try: pressing the unlock button on your fob. Failing that, pressing it rapidly several times in a row. Failing that, sticking the key in and turning the ignition on.

Again someone may correct me :D but if the battery is that weak it may need some charging before the above works.

Originally Posted by AndrewJames (Post 2867141)

Someone may correct me but I think some of the alarm systems have some sort of backup battery? So perhaps the car last remembers being alarmed, you've then gained entry to the car with the actual key and introduced some power to the battery resulting in the alarm?

To stop the horn sound I would try: pressing the unlock button on your fob. Failing that, pressing it rapidly several times in a row. Failing that, sticking the key in and turning the ignition on.

Again someone may correct me :D but if the battery is that weak it may need some charging before the above works.

Originally Posted by marinabrian (Post 2867167)

Andrew the BBUS or Battery Back Up Sounder is the upgraded alarm siren fitted to cars with headlamp wash, or as an upgrade to the standard alarm sounder.


If it's chirping, it is because it's internal battery is knackered, so it's a case of either unplugging it and charging the main battery, or better still fit a decent used unit as more likely as not, you will find the internal cells will have leaked and damaged the PCB.

That's why I posted the eBay link for Adam ;)

Brian :D