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Old 12-17-2012, 03:39 AM   #9
h1drojen
Registered User
 
Join Date: Jul 2011
Location: Reading, Berkshire
Posts: 1
My Ride: 325ci
Facelift Coupe (UK - 55)

Last year (Dec 2011) my e46 developed the dreaded "random" alarm problem. Took it a local mechanic who replaced the siren saying that it looked rusty and was very likely faulty. The bonnet/hood switch was also replaced. Cost me a total of about 200 (110 for the siren).

Last weekend (Dec 2012) I parked out side a video shop, chose a few movies and came back to a screaming car. Been using the key-in-door to lock the car since before tackling the issue myself and here's how:

(Note there are a lot of forums describing how to remove each of the sensors described so I won't go into those details.)

Removed the bonnet/hood switch, shut the bonnet, armed the car, waited 30 seconds, ALARM went off .i.e. Not the hood switch
Removed the tilt sensor in the boot/trunk (above the battery), armed the car, waited 30 seconds, ALARM went off .i.e. Not the hood switch
Removed the interior motion sensor in the car, armed the car, waited 30 seconds - NO ALARM (possibly this unit, however the car had no sensors at that time either)

Took all sensors indoors, sprayed WD-40 on the bonnet/hood switch to clean it up a bit.
Didn't want to tamper with the tilt sensor. Shook it a bit listening for any loose pieces. No noises.
Removed the interior motion sensor from its casing and simply blew both sides of it to clean out any possible dust.

Replaced the bonnet sensor, armed the car - NO ALARM.
Replaced the tilt sensor in the boot, armed the car - NO ALARM.
Replaced the interior motion sensor, the car - NO ALARM.

To make sure the alarm actually does works:

Lowered the front windows, armed the car, waited 30 seconds, stuck my hand in through one window - ALARM!!!!

No parts required. Now that I've done it I would say it can be done in 45 mins.
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