Author Topic: Alarm randomly going off  (Read 445 times)

Offline Borbus

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Alarm randomly going off
« on: 17 January 2021, 21:25 »
Twice now my alarm has randomly gone off. First time was in a car park. When I came back the hazards were going off. I assume the siren/horn had stopped sounding by that point. Happened again today at home. This time the siren was going off so I could hear it.

I've read a few places online that it might be the siren going bad. That's a £150 part and needs drilling out  :sad:  Are there other possibilities? Anyone dealt with this?
2010 Mk6 GTI

Offline Snoopy

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Re: Alarm randomly going off
« Reply #1 on: 18 January 2021, 11:00 »
Ultrasonic sensors go faulty.
Try turning off the interior sensors and see if it does not false alarm.
Bonnet switch.
Have read they can go faulty.

If its the siren or theres a fault on alrming. The led on the door will flash a sequence when you arm it to tell you there is a fault. Cannot remember how many flashes meen what. But I did see it online many years ago. A google search should find the info.
Current VWs = Mk6 GTI,  Mk1 GTI,  Mk1 Leon.
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Offline Borbus

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Re: Alarm randomly going off
« Reply #2 on: 18 January 2021, 17:27 »
Interestingly I did open the bonnet just before the most recent false alarm. I didn't realise there was a switch under there. Hopefully just gone stick or something. I'll check the LED next time I lock it.
2010 Mk6 GTI

Offline Borbus

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Re: Alarm randomly going off
« Reply #3 on: 23 January 2021, 13:59 »
OK so it went off again today. Both times when I was at home. I had parked it away from home twice, but maybe not for that long, and it was OK. At home it has now gone off twice. After about 30 minutes after locking it I would say.

The LED on the door does flash quickly, 7 times, before it goes to normal. Can't seem to find what this means online, though.
2010 Mk6 GTI

Offline Borbus

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Re: Alarm randomly going off
« Reply #4 on: 23 January 2021, 14:30 »
OK, so I'm showing several codes about alarm horn being faulty, so I guess that's it.

Trouble is it's now going off every few minutes. Any ideas how to disable the alarm completely? I've resorted now to just no locking the car, but I've a feeling it will lock itself before long. If I can't figure it out I'll have no choice but to disconnect the battery until I can get this alarm horn replaced.
2010 Mk6 GTI

Offline SRGTD

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Re: Alarm randomly going off
« Reply #5 on: 23 January 2021, 17:38 »
I owned a Vauxhall many years ago where the sounder / siren had an integral back up battery that failed while the car was under warranty. The alarm would go off shortly after locking the car, and the only way to silence it was to leave the car unlocked (fortunately, I garaged the car, so it wasn’t left unlocked in full view of others). The sounder / siren unit was replaced under warranty and didn’t cause any more issues.

I don’t know if VW alarm systems have a similar back up battery but if they do, maybe that’s the cause of your problems. Also, is your 12v car battery in good health? With many cars being used less during lockdown, if your battery isn’t holding its charge through lack of use, then could that be the reason your alarm is sounding?
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Offline Snoopy

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Re: Alarm randomly going off
« Reply #6 on: 23 January 2021, 19:01 »
Did you try turning off the ultrasonic interior protection with the button. Temp changes set these off if yhey are starting to fail. Would explain the time before false alarm
Current VWs = Mk6 GTI,  Mk1 GTI,  Mk1 Leon.
I should have bought a CSS in 2016.

Offline Borbus

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Re: Alarm randomly going off
« Reply #7 on: 24 January 2021, 14:22 »
I did, yeah. I tried both with the interior button, and by pressing the key fob twice (not sure if this actually does disable it, though).

My battery is showing 11.7V in OBD11. I assumed this was fine as it always starts fine and no other problems. But just reading about it now and it seems the voltage shouldn't ever be below 12V. Will test the voltage with a multimeter now...
2010 Mk6 GTI

Offline Borbus

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Re: Alarm randomly going off
« Reply #8 on: 24 January 2021, 14:54 »
OK, so the voltmeter shows 12.2V at rest (it's about 0 degrees today).

10.4V minimum when starting and 14V while idling (both seem normal).

12.2V is a little low... The battery says min 12.4V on it. Low enough to cause this, though? I do hope so as changing the battery is easy.

I can't see any record of it being changed. It's a Bosch S4 005. Is that the original?
2010 Mk6 GTI

Offline Snoopy

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Re: Alarm randomly going off
« Reply #9 on: 24 January 2021, 20:25 »
As reference. My leons siren went off today when i tried to start it with a low battery as ive only used it once this month. So I would say if the voltage drops low it seems to set the siren off probably using its own battery backup.
So maybe.
« Last Edit: 24 January 2021, 20:27 by Snoopy »
Current VWs = Mk6 GTI,  Mk1 GTI,  Mk1 Leon.
I should have bought a CSS in 2016.