Hi
@zixel I have just ''borrowed' this from another forum, it might be of some help ?
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For those still pondering over the Z3 alarm system, there are only a limited number of things that can go wrong with it. Check each of the sensors in turn:
* Bonnet switch - these seem to have a short plunger, which has been superceded by the one off the X5 in the parts catalogue - you can either fit the longer plunger version or adapt the existing one with some padding.
* Radio switch - wired in parallel with the bonnet switch. It relies on the prong on the back of the radio depressing a microswitch in a little cradle. Some aftermarket stereos don't fit this properly and in other cases it has not been refitted, hence the bonnet switch won't trigger the alarm.
* Interior sensors - there a couple of types, but most UK zeds have ultrasonic sensors, which can be prone to false alarms. Try setting the alarm without these active - press the lock button again on later alarm or press the LED on the earlier type. Note that the official BMW cure for a dodgy ultrasonic module is to replace it with a microwave one!
* Door switches - these are peculiarly located in the back of the door catch at the back of the door opening (most cars have a plunger at the front). These can wear and eventually not make proper contact. If this is faulty you will usually find the interior light behaves erratically.
* Boot switch - this is located in the boot lock in the boot lid - it is NOT the plunger things either side. There is a conical piece in the lock plate on the car that goes into a corresponding hole in the lock and depresses a microswitch in the bottom. Fairly evidentially the wiring for this goes through the know weak-point of the boot lid wiring - so broken wires in there can wreak havoc.
* Tilt switch - located in the left-had well behind the rear wheel - you'll need to have the trim off to find it. The well often fills with water and this can cause problems with the tilt switch. The tilt switch is disabled in the same was as the interior sensors.
The later alarm logs codes telling you which sensor (or approximately which in the case of the bonnet and radio switches) tripped the alarm and these can be read back with appropriate equipment. You may need to clear the codes and then read them again after is has gone off, as we have all managed to trigger the alarm accidentally by opening the boot with the key!
The later alarm can be unset by putting the key in the ignition and turning it to position II. This is handy if your remote battery goes flat as it uses only the car's own power to read the immobiliser chip in the key.
The earlier alarm cannot be unset except by some very nefarious means involving the removal of the glovebox. It can however be silenced by means of a small key in at the siren. This only turns off the siren, the indicators will continue to flash.
One final note. Microwaves do seem to set off the Z3 alarm. I have twice triggered the alarm on my zed simply by working on my other car (which has a microwave alarm) right next to it. It has also been noted that minicab radios are very good at doing the same thing - usually at about 2am.
