Folks,
Are the air pressure sensors on alarm systems subject to ageing? Can they be tweaked and fettled to sort them out?
My new XM's triggered the other day. Being a "gadget barge", it has a feature to allow you to disable the sensor (if you wish to cook your Labrador on board whilst you nip into Tesco, but not alert anyone). This worked and stopped the retrigger.
I recall having the same trouble on a company BMW. It usually happened after a long run on a cold day, and was something to do with the air in the cabin contracting as it cooled and setting the thing off. Or stuff creaking as it contracted.
On the other hand, the sensor may simply be "k*******d"
Any thoughts.
(Yes, OK, it is an XM, and, by nature, "electrically haunted")
rg
|
|
These are not pressure sensors but ultrasonic transmitters and receivers and yes there is a sensitivity control for them. The alarm may be being triggered by the circulation of air cooling rapidly due to the weather. Ihave to turn mine down in the winter ( Scotland ) so often frosts. Peter
|
|
|
First thing to check is that the seatbelts have fully retracted. I used to have alarm probs - later discovered that the seatbelts were causing the problem.
My mates alarm used to be falsely triggered by leaving the side window air vents open. On a windy day it would change the airflow inside the car, thus setting off the ultrasonic sensors.
Spiders, flies, and other creepy crawleys also have a habit of triggering the sensors as well.
|
Thanks, gents,
So these sensors are based on sound (rather than air pressure as the Citroen manual says?.)
Would the hallmark creaking French trim (contracting with cooling) cause the problem?
This is uncharted territory for me, as I've either owned company cars, or my own that have never been worth nicking.
Plus the XM comes with it's own theft repellent anyway...
rg
|
>> So these sensors are based on sound (rather than air pressureas the Citroen manual says?.)
No, they are triggered by air pressure. eg, if some lowlife breaks a window or opens the door, the air pressure in the cabin changes, thus triggering the sensors. However they can also be triggered by movement, eg, waving a hand in front of them or a fly buzzing around inside the cabin.
|
..so are they adjustable, and would the "cooling air" theory make sense?
rg
|
..so are they adjustable,
The aftermarket ones are certainly adjustable, but not sure about factory fitted ones.
and would the "cooling air" theory make sense?
I suppose the way to test this theory is to let the interior cool before setting the alarm by opening the doors or windows for a couple of minutes after you've parked up.
|
|
Sound and air pressure are the same thing. Variations in air pressure vibrate our eardrums and we hear a sound. A few years ago I bought a cheap home alarm operated by changing air pressure, the sensor was a diaphragm which moved when affected by a SUDDEN change in air pressure. An adjustable bleed hole led to the back of the diaphagm and allowed the pressure to equalise when there was a SLOW change in air pressure. This meant that a room door could be opened slowly and not set off the alarm, but a loud noise, being a sudden change in pressure would set it off. Modern cars are designed to run with a slight positive pressure in the cabin - it helps to to keep fumes out and prevent minor water leaks. This pressure is often controlled by simple rubber flaps covering vent holes (usually hidden away in the boot area) I suppose that with a well sealed car the pressure could change slowly when parked and then equalise rapidly when something 'gives' - altering the air pressure suddenly enough to set off the alarm.
|
Rob,
Ahhh the Citroen "character", can't beat it. How are you doing with the fuel consumption on this super barge?
Interestingly the previous owner of our new-to-us '93 Citroen TD (with a very similar OE fit alarm) told us not to bother using it because of false triggering.
I've found by making sure the sunroof, all windows and the face level vents are tightly closed it's been no trouble.
Some say if you have a position on the heater to set the airflow to off or recirculate this can help.
MM
|
MM,
Well, I wondered how long it would take before a Citroen devotee would come along and say "welcome to the fraternity" in their own unique way.
MPG? Late-thirties on urban-ish cycle with occasional A-road blasts to clean out the system (my excuse). Plus much enjoyment of the grunt of this device coming out of bends and roundabouts. No long-haul as yet.
I think some research with vents closed, hot air flushed out should do it. Plus the handy button that inhibits the sensor.
As I said, I had a BMW which did the same thing.
Thankfully, the XM has "stealth security". Horror stories of "ghost in the machine" faults are enough to scare crooks off. I hope.
Thanks, all.
rg
|
|
|
|
Rob
Hope you're enjoying the XM apart from this.
My first one suffered from false triggering from new, I had to disable the alarm with the key (it had a switch under the bonnet for this) and the dealer later fixed it quite simply. So there could well be a sensitivity control - sorry, I don't where though. After that, it was things like flies or stickers falling off the windscreen that triggered it, so it must be quite sensitive.
It can also be triggered by voltage changes (try arming the alarm with the hazard flashers going!), so that's another possibility, especially if the battery's a bit suspect.
Failing that, you can deadlock the doors by holding the key in the lock position for a few seconds. This also activates all the alarm LEDs, so potential miscreants are still deterred.
HTH, Happy XMing :o)
Terry
|
Thanks, Terry, thanks all,
The XM is superb. Dollops of torque, velvety ride, but taut enough on "normal" setting to allow lively driving.
Strangely enough, it does not feel like a barge at all once on the move. A bit like those, errm, "robust and statuesque" ladies who have the gait of someone half thir size. Compare and contrast with waifs who stomp like brewer's drays.
I ask Mrs Govier not to fiddle with buttons (on the car...) when we are on the move as I have memories of the 007 Corgi DB6 that shot the passenger out of the roof. It's that kind of car.
Long may the honeymoon continue. Thanks, Terry, for the help and advice in the "decision process" (which started around April, I recall). BTW, am I right in thinking that there is some kind of device that stops the car rolling backwards once you have released the normal brake? I seemed to be able to cope with hill starts without recourse to the foot-operated parking brake. It just seems to give the driver enough time to engage the clutch.
rg
|
Rob
My ZX does the same. Citroen checked it out when I got it (not from new) and said all the alarm parameters were within tolerance limits. Whatever that meant. I have found that shutting the ventilation to off has improved the situation. It's not cured - you can still set it off by driving past in a bus - but I think it's better than it was.
GJD
|
|
|
Rob
Both my XMs were automatics, so I didn't have to use 2 left feet for parking brake and clutch! All I did was hold a foot on the parking brake without engaging the lock and pull away. I assume if you had to use it you'd have to lock it on and release it with a bang as you pulled away.
Now some passengers I wouldn't mind shooting out the roof.....:o)
Terry
|
|
|
|
|
