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alarm goes off sporadically

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When I lock my car ('99 911 C2 coupe), the alarm will go off from time to time. Disturbs the neighbors.

Tried taking out the horn fuse (row 2, #3). Alarm still goes off.

My question: until I get this fixed, is there a fuse I can take out, such that I can lock the car, but disable the alarm? Of course I'd like the alarm on, but this is a stopgap. At least 3 fuses in the diagram seem to be linked to the alarm, so I want to make sure I'm taking out the right one.


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Fuse - not easily accessed.

I suggest you someone with Durametric software, a Porsche PST2, oe Porsche PIWIS diagnostic tool to read the alarm control units fault code(s).

From this you will narrow the zone (trigger) that is causes the false alarms. Or it could even be a bad control unit (if it got wet).

The alarm system, door locks, and drive block (immobilizer) are all part of one control unit - so disabling only one is very difficult.

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No good removing the horn fuse - the alarm has a separate horn. It may also have a separate siren and tilt sensor if the option was specified when new. Also, if you remove the alarm fuse, you won't be able to fully lock the car.

As Loren says, a diagnostic check will tell you what is setting it off. However, the most common cause of random false alarms is a faulty interior monitoring sensor. You can disable this by double-locking the car (two turns of the key, or two pushes of the remote button). This sets the alarm, but disables the interior sensor.

If you have the tilt sensor (a clear plastic unit, to the right of the battery as you look at it) check that it hasn't filled with water, which also causes false larms. You can disable this by unplugging it.

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