Help needed please, Alarm/hazard
 

Help please Alarm/hazard light issue.

I own a 2007 D5 with 40k on the clock and I have been having some issues with my alarm for a while now.

Initially as with countless other owners the alarm for no apparent reason would sound (usually in the night).

Forums suggest that the issue is most likely either

1 - Battery which i have replaced

2 - Siren - The alarm on my 2007 model is sounded through my horn sirens under the bonnet not a separate unit under the wheel arch which i believe is the case on pre - 2006 models

3 - Wifi interference which i have ruled out

4 - MMS unit which is know my last hope

I have managed so far to save myself a trip to my Dealer by removing the 15 amp fuse that sounds the horn when i am not driving the car. This has stopped the noise but does not stop the hazards flashing when the alarm is triggered which has not been a major problem and has served me well for months now.

Tonight things have escalated and i do not know if i have a separate issue or if everything is connected, hence my post for help and advise.

I noticed this evening that my hazards were flashing as per usual when the alarm is triggered but after a pause of no more than a few seconds they would start again and this was constant for well over 30 mins. A series of strange happenings then unfolded -

1 - i try to unlock the car with my key fob and nothing happens (fob seems dead - coincidence?) so unlock the car with the key.

2 - when i open the door an alarm sounds i have never heard before, not the horn sirens as usual (it looks like there is a separate siren somewhere after all)

3 - turn on the ignition key, new alarm siren stops sounding but hazards continue to flash. Turning on and off the hazard switch seems to stop the flashing momentarily but would soon start flashing again.

I have had no other choice than to disconnect the battery which in turn as now left me unable to lock the boot.

I really hope someone can relate to the above issues and point me in the right direction.

Sorry for the long post and thank you in advance for any help.

I would try disconnect siren and keep car unlocked for a while but...
... its likely CEM is "kaput"
You have one of the typical CEM failure problems - alarm goes off randomly for no reason

What is the CEM mate?

Cheers.

Did you replace the main vehicle battery or the alarm siren backup battery (internal, inside the siren)?

The backup batteries inside the siren fail after a number of years, the cure is to replace the battery or replace the siren - mounted inside the front right wheel well, need to remove wheel and wheel well cover to access the siren.

However the occurance of other issues at the same time point to possible CEM water ingress and corrosion damage, caused mainly by leaking sunroof drains.
Does your car have a sunroof?
Is the carpet wet / damp in the front? Check left and right sides. If damp / wet, then suspect a sunroof drain blockage and leak. Lots of info here on this forum on how to test, identify and correct leaking drains.

The CEM, if affected, will need repair or replacement. Repair by the guy in London is much cheaper than replacement.
To determine CEM state, remove and inspect for any signs whatsoever of water damage. Look for water marks and corrosion. It should be bone dry and maybe dusty, must show no signs of water stains whatsoever.

Thank you for all help so far.

To answer some questions -

It is the main vehicle battery that has been replaced, my XC90 does not have a sunroof and all carpets are dry.

Update -

Reconnected the battery today and all seems once again to be fine and the key fob is again working. I am still keen to receive any further help and advise as i am sure this will happen again.

Regarding my Alarm issue can someone please clarify -

My alarm like many other XC90 owners occasionally goes off for no apparent reason. When this happens it is my horn siren that sounds and hazard lights flash.

As a short term fix i have been removing the horn fuse when not driving the car. This has worked well up until yesterday and on the odd occasion when the alarm is set off just the hazards have flashed which is no big deal.

Yesterday hazards were flashing continuously, key fob did not work and when i opened the door a completely new siren was sounding not the horn sirens which were still disconnected by the fuse.

Can anyone explain exactly how the alarm system works regarding horns/sirens and what the siren was that i heard yesterday if it is not the horn that usually sounds when the alarm is set off.

Cheers, all help much appreciated.

Good that you replaced the main vehicle battery, this eliminates it as a suspect
The fact that you do not have a sunroof is good because it means you never have the risk of water damage to the CEM (Central Electronics Module, one of the main 'brains' of the vehicle)
Note that disconnecting the vehicle battery, waiting 15 minutes and then reconnecting is similar to rebooting a PC: it reboots the vehicle. This will often clear random faults.

The volvo factory alarm system sounds the vehicle horn AND has a siren with it's own internal rechargable battery

The fact that you do not recall hearing the siren means that the siren may be so faulty that it no longer sounds reliably.

The siren battery fails after a few years - somewhere around 10 years old - and one of the symptoms is the siren sounding all by itself.

The siren is connected via a digital LIN databus to the Upper Electronic Module (UEM) in the roof near the rear view mirror, and the UEM connects to the vehicle CAN bus.
A confused siren could possibly confuse the vehicle. Shouldn't, but could.

The siren is powered by fuse F8, located on the CEM.
The CEM is located on the left hand side lower area of the dash, above the footwell. To access it, remove the lower dash cover (which includes the courtesy lamp), and then locate the CEM
Videos here:
http://xemodex.com/blog/volvo-centra...70-v70-s70-s80

Locate F8 and remove it, that disconnects power from the siren.
Should the siren battery have some charge left, it may sound for a while until the battery is drained.

Then consider repair or replacement of the siren....

OR
Maybe you have a CEM fault caused by deteriorating solder joints.
If removing F8 does not stop the problem with vehicle remote unlocking reliability then consider sending the CEM in for check and repair to the London guy that specialises in them:
http://volvodiagnostic.com/shop/inde...duct&id_lang=1

Cheers mate, thank you for taking the time it is very much appreciated. So am i right in saying that if the siren is at fault and i disconnect it using the method above then this should stop any further false alarms and in turn also stop the main horn sounding?

Also, if the fuse just disconnects the siren would i be right in saying that the alarm system would still be active when the fuse is removed and any further legitimate alarm triggers would still sound the vehicle horn?

Thanks again.

Another quick update -

I have just gone out to the car and removed the f8 fuse but then remembered that i had done this before previously and that it had done nothing to rectify the car horn still sounding, because of this i previously then reinstated the f8 fuse. This is the reason why i have always assumed that the car horn was the alarm and i was not even aware of a secondary siren.

As i have only ever heard the car horn sound when the alarm is set off can someone confirm that this is right and that i should not be hearing the siren instead, not the horn.

Does anyone know why there is even a secondary siren installed and what is its purpose as i have never even heard it sound previously.

If as mine does still occasionally trigger and sound the car horn, am i right in assuming that with the siren fuse disconnected that this would mean that the issue is not with the siren itself?

Cheers.

Could someone please intentionally trigger the alarm on there XC90, 2007 model or newer and confirm whether it is a siren or the vehicle horn that sounds.

I am trying to work out whether or not i should be hearing the car horn when the alarm sounds as is the case with my XC90 or whether the horn should only be a sort of secondary back up if or when the alarm siren fails.

Cheers.

Hi,

Mine is a 2006 model so may be different, but I've just tried the alarm out for you:

With the car locked and alarm set, movement inside the car triggered the siren alarm, not the car horn.

With the car locked and alarm set, pressing the red triangle on the key fob set off the car horn alarm, not the siren!

Not sure if this is of use to you, but it appears that both alarms serve different functions!

Paul