Help needed please, Alarm/hazard

[steve0]

Originally Posted by SwissXC90

Are you sure the problem is not caused by the key fob being in your pocket and the red triangle PANIC button being pressed inadvertently? Due to keys or coins pressing on the button? Has happened to me when walking away from the car....

I would love to say this is owner error but as these false horn triggers usually happen in the early hours which result in me running down stairs to find my keys i am 100% certain this is not a case of accidental pushing of the red button

[steve0]

Originally Posted by cassell

Steve, looking at the comments made by others who seem very knowledgeable, I reckon something around your house area is working on the same frequency as your panic button!

We once had a remote control conservatory fan which worked on the same frequency as a neighbour three doors away, took us both weeks to work out why our fans and lights kept randomly switching on and off!!

I really hope this is the case because CEM replacement i am sure will dent the wallet hard.

I just cant think what would set off the panic button in the early hours when most wifi enabled devices are shut down. If the triggers were only happening in the day it would seem more plausible.

[steve0]

There are endless threads covering false alarm triggers all over the net but surprisingly nothing covering false panic alarm triggers.

Unless of course others like myself are mistaking panic alarm triggers for false alarms. If that is the case then hopefully this thread will at least help others regarding the difference between the two.

[SwissXC90]

Originally Posted by cassell

Steve, looking at the comments made by others who seem very knowledgeable, I reckon something around your house area is working on the same frequency as your panic button!

Not that simple.
Allmost all car remote controls in Europe operate on 433.92MHz.
They all share the same frequency band.

So why do they not trigger each other?
Remote keyless entry fobs emit a radio frequency with a designated, distinct digital identity code.
The distinct code is effectively unique for each key fob AND is synced to the car.
Typically, around 43 million possible key fob codes exist.

Techie stuff here:
https://en.wikipedia.org/wiki/Remote_keyless_system

Sharing the same frequency is very common.
Same frequency interference simple reduces the range of the remote, it does not cause the car to unlock.

[lloydman]

Hi,

has anyone managed to find a solution to this problem?
i have the exact same issue with my Volvo v50 2007.

i know its not the siren control module as i have removed it from the car.

any advice or what fixed this issue for you would be greatly appreciated.

when it happens it is the same as the panic alarm, hazards flash and horn honks.

[Bigjimknickers]

Originally Posted by SwissXC90

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

hello, my XC90 has had a new battery last month so I can tick that off, so the next step is to pull the F8 fuse?

[SwissXC90]

Originally Posted by Bigjimknickers

hello, my XC90 has had a new battery last month so I can tick that off, so the next step is to pull the F8 fuse?

On a MY2009 XC90, F8 on the CEM provides power to the siren.