Help diagnosing random alarm triggering

[John Brennand]

I have a new to me, 2006 2.5T XC90 - NO sunroof.

Recently the alarm has been triggering seemingly randomly once or twice a day. There are NO "messages" such as Alarm Service Required, nor are there any codes showing on VIDA/Dice - checked by my Volvo Indy dealer.

I know that the siren is a weak point after the batteries fail and leak and mine is of the age when its time is due. However, I has that problem on a previous XC70 and that went hand in hand with a code and Alarm message - I changed the siren and it fixed the problem. I am also aware that a faulty bonnet lock sensor can be a culprit. Also the Mass Movement sensor(s) have been implicated by others on here, as have spiders, iPads, coins, and bat wings.

So in an effort to pinpoint the cause (or causes) I have cleared out any electronic devices and coins and done a spider sweep. But still the alarm fired off. I have now "deactivated" the sensors with the dash button and so far the Alarm has not triggered. If I assume the situation remains the same what would be the next step ?

I have some questions - that answers to would help.

1) The data so far, suggests that the alarm is being triggered either by a faulty or super-sensitive MMS sensor - or by a stray electronic signal - if it were the siren or bonnet lock that was responsible there would be a code evident - is that correct ?

2) Are there 2 MMS sensors in this car? and if either go faulty would they not show a code?

3) If no code, is it possible that one of them has just come loose off its sticky tape backing thus making it more sensitive to a gust of wind or rampaging squirrel ?

4) Is it possible to turn down their sensitivity with VIDA/DICE ?

I know these are pretty expensive to change and clearly don't want to do that without good evidence

Any other suggestions or thoughts are welcomed

Cheers John

[gmonag]

Is the alarm sounding in the same location each time - radio interference?

Otherwise my money would be on the alarm/siren unit.

[John Brennand]

Originally Posted by gmonag

Is the alarm sounding in the same location each time - radio interference?

Otherwise my money would be on the alarm/siren unit.

I have recently started parking on the driveway and that's when the problem started. I will move back outside the house soon and see if that lessens the problem.

If it were the siren unit I am thinking it "must" throw a code or error message.

Cheers John

[gmonag]

A few years ago my neighbour's BMW started alarming on his drive and the cause was eventually traced to my wireless burglar alarm!

[SwissXC90]

Poor / dirty contacts or misalignment of the bonnet switch are the most common cause. The alarm thinks the bonnet has been opened

Remove and clean / adjust, then refit.

The switch is on the left hand side bonnect latch, and can received a lot of weather due to its position

[John Brennand]

Originally Posted by SwissXC90

Poor / dirty contacts or misalignment of the bonnet switch are the most common cause. The alarm thinks the bonnet has been opened

Remove and clean / adjust, then refit.

The switch is on the left hand side bonnect latch, and can received a lot of weather due to its position

Again... this should throw a code - shouldn't it ?

[AB-UK]

My Son's remote controlled car has set off my alarm before.
One week it went off 4 or 5 times in the golf club car park whilst I was playing.
Hadn't done it before that day, nor since.
Probably stray electronic interference from an unknown source.

[Simon Jones]

VIDA will show causes of activations as I recall.

[John Brennand]

Originally Posted by Simon Jones

VIDA will show causes of activations as I recall.

On VIDA today nothing reported other than confirmation of Alarm Activated. Or might he have missed it somewhere ?

John

[tdi]

He might have not found it as all alarm triggers can be read with vida.