Help diagnosing random alarm triggering
 

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

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

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

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 ?

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.

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

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