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-   C30 / S40 & V50 '04-'12 / C70 '06-'13 General (https://www.volvoforums.org.uk/forumdisplay.php?f=58)
-   -   Alarm keeps sounding (https://www.volvoforums.org.uk/showthread.php?t=298436)

GrahamV Sep 9th, 2019 17:39

Alarm keeps sounding
 
Hi
I have a 2011 C70. When I got back to the car yesterday there was an error message saying to check the car as the alarm had sounded (or words to that effect).
Then today, the alarm went off for no apparent reason

I'm concerned it may go off in the middle of the night and disturb the neighbours. Any ideas what I should be checking as I don't really know where to start looking

Thanks, Graham

phil1968 Sep 9th, 2019 18:26

https://www.volvoforums.org.uk/showthread.php?t=264425

GrahamV Sep 9th, 2019 21:47

Thanks for the link. That thread is about the alarm going off as soon as it is switched on.
Mine doesn't go off immediately, I am guessing/hoping maybe its a spider or something. Is that possible?

iainmd Sep 9th, 2019 22:23

It's fairly likely that the battery in the siren unit is shot. I had that on both the S40 and V50 so bought a newer second hand siren unit and swapped them over which solved the problem. Given your car is a 2011 model you'll struggle to do that so you can either split the siren unit open and change the battery yourself if you're moderately handy with DIY and electrics (there is a thread on the forum somewhere about this) or get a new siren unit from Volvo.

On a V50/S40 it's located in the plenum chamber under the windscreen at the rear of the engine bay, normally on the passenger side.

upv5 Sep 10th, 2019 14:29

My money is on the movement sensor located in the middle of the headlining, this often fails and just sets off the alarm for no apparent reason. Connecting to Vida will tell you what sensor set off the alarm for at least the last 10 occasions.
A temporary solution is unclip the sensor and disconnect the wiring, you will get an "alarm fault" on the dash every time you start the car but just clear it, hopefully the alarm will no longer randomly sound.
I bought one off ebay for £15 and it works OK.
If the alarm still sounds with the movement sensor disconnected I'm afraid it is another fault, best of luck.

John

phil1968 Sep 10th, 2019 20:49

Quote:

Originally Posted by GrahamV (Post 2552310)
Thanks for the link. That thread is about the alarm going off as soon as it is switched on.
Mine doesn't go off immediately, I am guessing/hoping maybe its a spider or something. Is that possible?

Sometimes it would take a while before the alarm would go off, usually in the early hours :rolleyes: The siren module internal battery has a life of 8 to 10 years, when it expires it gives the symptoms described. As per that link I posted I replaced the siren module about 18 months ago & it's been fine since.

GrahamV Sep 10th, 2019 22:36

Thanks again for the input.

Last night I took my chances and left the car unlocked so there was no risk it would disturb the neighbours. Then I locked it this morning and it didnt go off all day. Have unlocked it again for tonight. So have only had two false alarms so far
Following on from what John has said - I have a generic diagnostics machine, would that show the reason for the alarm sounding do you think?

I have tried to find a source for a new unit, but cant seem to find anything online (other than used one's on ebay that might also have battery problems I guess) - Would anyone know a good company to try?

Many thanks

upv5 Sep 12th, 2019 17:37

A generic code reader usually only reads engine faults where as Vida reads everything including alarm faults and it records alarm events and what sensor caused it. Disconnecting the Mass Movement sensor does not disable the alarm it just won't pick up movement in the car. When ours started playing up the alarm just randomly went off usually in the middle of the night.

John

srcholmes Sep 19th, 2019 19:06

I found that if I left my mobile phone in the car (with it turned on), that would trigger the alarm at random intervals...

Also, if you are worried, try turning off the motion sensors - press the left hand button at the map light cluster in the headlining just before pulling the key out after turning the engine off and getting out of the car. You should get the "Reduced Guard" message come up.

Thanks
Steve

GrahamV Sep 21st, 2019 21:45

Thanks for the comments
I haven't posted an update, as I have been monitoring things. I left it unlocked quite a bit so as not to disturb neighbours. But whilst on, it had behaved itself, but only until yesterday.
Your post got me thinking. Especially Steve's note about his mobile phone.

I looked at my user manual and it says one of the alarm sensors is under the cup holder of the centre console and that you shouldn't leave coins, keys, etc in the cup holder as metals can trigger the alarm.
Took a look in mine and I have £2, 4 x £1, 10p, 1p and for good measure, an old screw I found in the drive!
The coins are a relatively new addition as I had got caught out without money for a car park ticket. So I am hoping this might be the problem.
Still not brave enough to risk disturbing neighbours at night, but will see how I get on during the day
Graham


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