Alarm Sensors Issue

JohnB

Regular Member
Joined
Aug 23, 2020
Points
13
Location
North Wiltshire
Model of Z
Z3
Hi there I’m looking for some help with an alarm fault on my 2000 Z3 1.8. When the alarm is set it will randomly go off for no reason. I have tried unplugging the bonnet switch, and checked the boot for signs of water damage to the tilt sensor and can’t see anything untoward. If I press the lock button twice to disable the interior sensor, I get no unwanted alarms. I suspect therefore it may be a fault with the sensor inside the car. I’ve not been able to work out where that sensor is and I’m wondering if anyone has any advice on locating it and things to check as and when I find it! Many thanks.
 

DrWong

Zorg Guru (III)
Joined
May 8, 2017
Points
125
Model of Z
3.0i
Possibly the battery. I believe the alarm siren can trigger if voltage from the battery drops below a certain threshold, as it thinks someone is trying to cut power to the alarm system. You should see around 12.6v with a multimeter on a healthy battery.
 

t-tony

The Legend
Deceased
Supporter
#ZedShed
Joined
Dec 31, 2013
Points
226
Location
Torksey Lock,Lincoln, England
Model of Z
E89 Z4 23i Auto
I think I'm correct in thinking the alarm sensor is inside the rear view mirror housing?

Tony.
 

JohnB

Regular Member
Joined
Aug 23, 2020
Points
13
Location
North Wiltshire
Model of Z
Z3
Not checked the battery, but it seems strong and holds charge well when car left standing. Just grabbed a pic of the mirror... never noticed the wiring to it before. Does that support the sensor theory do you think... or heating?? I’d imagined you see a little grille with sensor behind or similar. Nothing like that. 😟
View attachment 154445View attachment 154445
 

Ianmc

Zorg Guru (IV)
British Zeds
The M44 Massive
Joined
Oct 12, 2014
Points
165
Location
New Forest
Model of Z
Z3 (M44)
Does it still go off with the under bonnet switch disconnected? The under bonnet switch is a known problem. Likely looks OK but only solution is a new one.
 

JohnB

Regular Member
Joined
Aug 23, 2020
Points
13
Location
North Wiltshire
Model of Z
Z3
Thanks for the response. Yes. I disconnected it for a few days and the problem remained the same.
 

Mint

Zorg Expert (I)
Supporter
British Zeds
East Anglian Crew
Joined
Sep 23, 2012
Points
222
Location
Stafford
Model of Z
2.2 Sport Individual
I believe there is a anti-theft trigger on the back of the radio, maybe worth checking that also...
 

JohnB

Regular Member
Joined
Aug 23, 2020
Points
13
Location
North Wiltshire
Model of Z
Z3
Thanks Mint, could indeed be worth a look. I’m thinking that it must be either the interior sensor or tilt sensor in the boot though because the problem goes away when I press the lock button twice on the key fob. My understanding is that deactivates both in case you’ve left a child/pet etc. in the car or locked it with the roof open. Threads on here say check boot for water in case the aerial grommet has leaked... damaging the tilt sensor, but mine appears bone dry... which leads me back to the elusive interior sensor. It seems the rear view mirror houses the remote central locking electrical gubbins but can see any evidence of alarm sensor, so still scratching my head a little as to where that might be! Might pull the radio out and check the switch anyway... original BMW unit so should be ok though. Appreciate the input. Thanks again.
 
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