I will preface this by stating I only have experience with the factory VW
alarms on A3 VWs (that's 1993-1998 Golfs and Jettas, and Cabrios of similar (but not exact)
vintage). I'm not sure if any A2s ever came with factory alarms... perhaps
some Corrados, but I don't know anything about them if that's the case.
Once again, I have noticed a trend in the search engine queries that lead
people to this site. It seems a lot of folks are looking for info on the
factory Volkswagen alarm; particularly, deactivating it and finding out why
it goes off when the battery is reconnected.
Okay, I think I know what the majority of the people looking for info are
*really* after... disabling the alarm altogether because they don't like
it when it goes off. Most common is the "my alarm goes off every time I
disconnect and then reconnect the battery, or every time I jump start the
car". As most VW geeks know, this is the way the alarm is designed - it
is intentional. The best thing to do when reconnecting the battery or jump-starting
the car is to have a friend standing ready to insert and twist the key in
one of the door locks as soon as the alarm goes off. Inserting the key
in one of the doors and twisting it in the unlock direction is the official
method for deactivating the alarm on these vehicles, unless you are lucky
enough to have a keyless entry system (in which case, you have a little
button on your key fob that will silence the alarm).
I'm afraid I can't endorse bypassing the factory alarm system (not that my endorsement
is actually worth anything). First of all, it's not a trivial task. The system was
purposely designed to be inaccessible and difficult to disable and/or remove. The Alarm
system is also integrated with the central locking system. Not only is it difficult to
bypass or remove the factory alarm, but it really shouldn't be necessary (unless you are
replacing it with an aftermarket system). Disconnecting the battery isn't something that
should have to be done on a regular basis, and likewise for jumpstarting. If
you're needing to jumpstart your vehicle all the time, you'd be best off fixing
the problem rather than killing the alarm. A consistently flat battery is typically
the result of a battery that will no longer retain a charge, an electrical problem
that is keeping the battery from being charged, or an electrical problem that
constantly draws power from the battery even when the car is off.
The other problem you may have with the factory alarm system is that it sounds
when it shouldn't. I had that problem on our 96 Golf. The alarm would sometimes fail to deactivate
when the doors were unlocked. When the alarm
did deactivate, it would reactive
itself again once the engine was started, and so opening the door again to get out of
the vehicle would cause the alarm to sound. It was incredibly frustrating, and it
took a whole night to troubleshoot. We started by checking the wiring that runs into the
front doors below the a-pillar (those accordion-like rubber boots that run between the front
of the front doors and the main body of the car). There are switches in the front door locks
that activate and deactivate the alarm system. When you lock a door, the alarm becomes activated
(meaning that it will sound if it senses an event). When you unlock a door, the alarm deactivates
and you can open doors without the alarm sounding. My first thought was that there was
either a nearly-broken connection in the wire providing the deactivation signal, or a short
involving the wire providing the activation signal... or perhaps some combination of both.
Everything seemed to check out, though - the switches were still intact and functioning correctly,
and the wiring going into the body of the car from the door was just fine. After studying the
wiring diagrams in the Bentley book for quite a while, it seemed that the central locking system
control module was related to the alarm system. The central lock module itself is located in the
rear of the car, in the luggage compartment. It will be encapsulated in a 2 piece styrofoam shell.
In Jettas, it is on the driver's side of the car,
up against the side of the luggage compartment (pull the carpeting back the goes up that side, and
you will see it wedged in the body panel above the fender). In Golfs, it is on the passenger's side
of the car, just next to the tail light (you will have to pull back the carpeting going up the
side of the compartment in order to see it). The vacuum pump for the locking system (the locks
are vacuum actuated) is contained in the same housing as the electronic control module, so don't be
surprised when you see a vacuum line attached to it. If you need to disconnect the vacuum line,
squeeze the base of the connector with a pair of pliers, and you should be able to work it free.
If you are having funky alarm problems, then try disconnecting the electrical connections going
to the central locking module and see if the problem goes away. If so, then the locking module
is your problem. That's what my problem ended up being. Opening up the module housing, we
found some water inside it, and the circuitry was badly corroded and burnt. You may want to buy
this part used if you need to replace it. New ones are $280 and upward, as of this writing.
