Alarm Siren triggers when locking car


Registered User
Apr 9, 2012
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When I lock my A3 2001, the alarm triggers. I've looked on vagcom and the error is 'alarm was triggered by internal monitoring'.
I cleared the codes, pressed the button to disable the internal monitoring, locked the car and it still goes off with the same error code.

What's the next step in diagnoses please?

The first place I look when any VAG car of this vintage starts to have alarm problems is the alarm siren unit.

My dad's 2003 A4, my previous 2002 A3 TDI quattro, 2001 A4, and my current S3 have all needed new sirens at around the 10 year mark.

If it's interior activation, check there isn't anything living in the sensor up near the interior light (spiders etc!) although I suspect if it's still happening with the interior monitoring switched off it'll be the siren and circuit board.

As per other threads recently, the rechargeable batteries inside leak over the circuit board, and you get all kinds of bizarre alarm behaviour including siren on locking, ghost activations and even in my Dads case the alarm going off even when the car was unlocked.

It's worth a look anyway, especially if VCDS isn't showing any other faults.
Thanks. I didn't have much time today but when the alarm triggered I looked in the left side (looking from back) boot compartment because that's where the siren noise comes from. Then I realised the noise appears to be coming out of the speaker or subwoofer thing, unless the siren is next to that somewhere??