Car alarm going at random intervals

[david25]

Hello, any tips to diagnose why my car alarm is going off at random intervals?

Sometimes, it will be completely normal, lasting two days. But other times, I can lock and within 30 minutes its going off?

This also happens when the interior sensors have been deactivated using the button the B pillar.

Will a code reader capture anything? I can order a Bluetooth dongle if you think it will help. The car is a 2011 GTI, the main battery was replaced in June this year.

Thank you

[Snoopy]

I know vcds will tell you not sure about a generic scanner. It might as it should show you a code. Which you can then look up on VCDS wiki Internet page.

Known causes are:
 backup siren battery (normally only flashes lights no siren)
Bonnet switch.
Boot switch
Door central locking motors.

[david25]

I know vcds will tell you not sure about a generic scanner. It might as it should show you a code. Which you can then look up on VCDS wiki Internet page.

Known causes are:
 backup siren battery (normally only flashes lights no siren)
Bonnet switch.
Boot switch
Door central locking motors.

Backup siren battery (normally only flashes lights no siren), the siren is sounding so maybe not
Bonnet switch, OK its possible
Boot switch, OK its possible
Door central locking motors, the central lock locking seems to be working properly.

I have amazon delivering a OBDeleven (the basic version) tomorrow, is this good enough?

[david25]

Update, OBDeleven claims the following faults

Alarm horn, no signal/communications 01134 static
Alarm horn, lower limit reached 01134 intermittent

http://wiki.ross-tech.com/wiki/index.php/01134 Says

Possible Solutions

Check Fuse(s)
Check Wiring and/or Connector(s) from/to Alarm Horn (H12)
Check/Replace Alarm Horn (H12)

Ross-tech links to this page https://www.ttforum.co.uk/threads/2010-2-0-s-line-alarm-going-off.1834061/
which is all about replacing the battery unit, look for the £200 quote post from 2018, so more expensive now!

He claims the battery life is 10 years, my car is 12 years old.

Should I book in for a replacement or should I perform more diagnostics?

[Snoopy]

That's what I thought it might be but it often mutes the siren.
Mines had 2 replacements in 14yrs. 
There are two different makes and they arnt interchangeable from what I've been lead to believe. So you have to remove it and see what make it is as they were both fitted during the same production years.
Bosch 1K0 951 605 C
Cobra 1K8 951 605 B
The last letter is the revision so a new one may have a later letter.
If you find out how much one is now could you let me know.

[david25]

Will do, I plan to phone around this morning.

Do you know the official workshop time to replace the unit?

[Nino]

Will do, I plan to phone around this morning.

Do you know the official workshop time to replace the unit?

You mean time to replace battery or Siren in the wing?

Ether way, Battery will take around 10mins max, Siren will require the wing to be removed and possibily the bumper too so allow 3 hours (Thats being genious)

[david25]

Will do, I plan to phone around this morning.

Do you know the official workshop time to replace the unit?

YOu mean time to replace battery or Siren in the wing?

Ether way, Battery will take around 10mins max, Siren will require the wing to be removed and possibily the bumper too so allow 3 hours (Thats being genious)

I mean the alarm siren unit which contains a battery, pics here
https://www.briskoda.net/forums/topic/457543-alarm-siren-replaced/page/2/

Not the main 12v car battery.

Three hours sounds like a big workshop bill!

[david25]

Cost for Bosch 1K0 951 605 C is £235.80

[Snoopy]

Thanks for the price update.

I did have the official procedure but cannot find it at the moment.
Anyway its,

Wheel off
Remove Wheel arch liner
Drill out the two rivet holding metal box over alarm unit
Remove box with siren,
Unplug siren.
Lift siren out of metal box.
Then refit is reverse, but you need two new rivets.

Not hard, you would think even a VW tech could do it   

The first one mine needed was still under warranty, the dealer refitted the wheel arch liner back on with I'm guessing an electric screwdriver and the screws so tight  they cut right through the soft wheel arch liner plastic, result when i checked, new liner needed and another trip to the dealers...