How do I stop the alarm going off Xantia II

This is the Forum for all your Citroen Technical Questions, Problems or Advice.

Moderator: RichardW

rmunns
Posts: 591
Joined: 09 Jul 2009, 22:09
x 5

How do I stop the alarm going off Xantia II

Post by rmunns »

More and more over the past 3 months the alarm will go off without obvious cause on my year 2000 Xantia Hdi90 saloon. When I leave the car, I lock and alarm with the 'blip' but probably on one in three occasions the alarm will go off. Usually after only two or three minutes, sometimes after 20 or 30 minutes.

I have tried double locking (deadlocking) but I have not tried pressing the occupancy button inside, which I understand is if you want to alarm while leaving a pet / person in the car. Might this be a way to avoid the alarm going off?

At one stage I thought it might be because I was leaving the windows a little open, but no, that is not the cause. Neither is ambient temperature, because it has happened on very warm days as well as when it is cooler and raining hard.
User avatar
CitroJim
A very naughty boy
Posts: 43889
Joined: 30 Apr 2005, 23:33
x 1784

Re: How do I stop the alarm going off Xantia II

Post by CitroJim »

Most likely the ultrasonic transducers. Try setting with them disabled. press the alarm reset/ultrasonic disable button (the one with a crossed-out speaker symbol on it) just after switching off the ignition. Hold the button until the LED by the driver's door mirror (the one the normally flashes when the alarm is set) lights up solidly. Now lock normally.

If the alarm is now happy then QED..

A Lexia diagnostic will read the last 15 alarm triggers to aid your discovery of the cause.

The next best culprit is the boot switch. This is a little switch that is operated when the boot is shut. The brown connector for it can be found just under the boot carpet near the lock hasp. Disconnect the brown plug and the switch will be inoperative and will appear to the ECU as if the boot is always shut. The bonnet has a similar one.

Does the alarm 'peep' on setting? If it does then this indicates one circuit or another is faulty and the alarm is not setting correctly.
User avatar
Mandrake
Posts: 8438
Joined: 10 Apr 2005, 17:23
x 423

Re: How do I stop the alarm going off Xantia II

Post by Mandrake »

Same problem with the alarm in my V6 - lock the doors with the remote and almost without fail the alarm will go off in 5 - 10 minutes. Haven't had time to troubleshoot it.

I'd try setting it with the ultrasonic sensor disabled but the problem is the car is parked about 25 metres away from my 2nd floor apartment so not only might I not hear it if it went off, (annoying the neighbours) I couldn't shut it up without a trek down stairs and out into the car park when it inevitably chose the middle of the night to go off ;)

If I could disable the siren but leave the alarm active (the LED shows that the alarm has gone off in your absence ?) I'm sure a bit of trial and error would let me figure out which sensor it is, but I understand disabling the siren is lexia only, in which case if I had access to one I could just read the fault log anyway...

One other thought I have with mine - the clock frequently resets itself to midnight, sometimes a couple of times a day or more, suggesting that there might be some sort of electrical fault. I've even noticed the cabin fan sometimes cuts off completely for a few seconds and comes back on while driving, often when hitting a bump.

Perhaps an electrical fault could be fooling the alarm into thinking someone is tampering with the battery ? (presumably disconnecting the battery while armed would trigger the alarm...)
rmunns
Posts: 591
Joined: 09 Jul 2009, 22:09
x 5

Re: How do I stop the alarm going off Xantia II

Post by rmunns »

Just an update, CitroJim....................... I disabled the ultrasonic detectors and the alarm has not gone off this time. We are on holiday and I could lean out of window to shut alarm off, but then the car was unprotected, not good. I'llcontinue to disable each time I leave car and we'll see if this solves it.
User avatar
Mandrake
Posts: 8438
Joined: 10 Apr 2005, 17:23
x 423

Re: How do I stop the alarm going off Xantia II

Post by Mandrake »

I worked up the courage to set the alarm with the ultrasonic sensors disabled via the dashboard button, and its now been nearly 8 hours without the alarm going off, (touch wood, I'm about to go to bed!) normally it would go off in 5-15 minutes without fail, so I think thats the ultrasonic sensors fingered as the culprit. :twisted:

Question is, what to do about it. How repairable is this fault ?

Is it likely to just be a fault with the actual ultrasonic transducers themselves ? (If so, where would I find replacements...)

Dry joints on the sensors or faulty wiring ?

A fault in the alarm box itself ? (where ever that is)

Meanwhile is there a way I can disable them without having to remember to press the button every time ? If I just disconnect the transducers will that shut it up, or is that going to cause the alarm to fail to arm, or just go off after the 45 second arming delay ?

Is it possible to disable the ultrasonic sensors permanently with a Lexia, or can a Lexia only disable the entire alarm ? Either way I don't mind too much, I mainly just want to be able to lock the car with the remote, I'm not so bothered about having the alarm working, I've never had an alarm in any previous car I've owned, and it is a 14 year old Citroen, not high on the wanted list for thieves. :roll: If its not too difficult or expensive to fix I don't mind having a go though.

Any advice on how to fix it now I know its the ultrasonic sensor would be appreciated. :)
User avatar
CitroJim
A very naughty boy
Posts: 43889
Joined: 30 Apr 2005, 23:33
x 1784

Re: How do I stop the alarm going off Xantia II

Post by CitroJim »

Ahh well, that's a nice QED on the sensors then :-D It'll be them, no doubt. They're still available from Citroen but quite pricey. I'd love to know if there's an aftermarket alternative that might work too..

No, as far as I know the Lexia cannot permanently disable them. I've looked. For now you'll just have to get in the habit of disabling them before you lock the car.

The alarm is part of the CPH which lives behind the dash in the vicinity of the passenger airbag... It won't be that causing it or if it was, I'd be very surprised...
RichardW
Forum Treasurer
Posts: 9646
Joined: 07 Aug 2002, 17:12
x 489

Re: How do I stop the alarm going off Xantia II

Post by RichardW »

There appear to be two types - one with a Diode one without (is that in fact the LED?). Without listed at £33.65, with listed at £96.61 :evil:

Both are now NFP unfortunately :roll: What happens if you just unplug them? Could you fit a resistor instead to fool the alarm if required?
User avatar
Mandrake
Posts: 8438
Joined: 10 Apr 2005, 17:23
x 423

Re: How do I stop the alarm going off Xantia II

Post by Mandrake »

Bother. Don't like the sound of them being expensive, but surely they're standard ultrasonic capsules ?

Do you think it's worth disconnecting them to see if that disables them ? I guess it's possible that may just cause the alarm to fail to arm, or go off after a few minutes.

One devious way I can think of to trick the alarm into believing everything is ok and the sensors are working is to disconnect both, figure out which one is being used as the speaker, then take its output and feed it to the input that normally goes to the other sensor via an appropriate L-Pad - presto, the alarm thinks both sensors are working.

All they do is emit an ultrasonic tone into the car and monitor it for any changes in amplitude that are caused by changes in reflective surfaces as objects move in the car or glass is broken. A constant tone at roughly the right amplitude being fed into the input will be an "everything is ok" signal...

If I had the circuit diagram, or at least a pinout with the expected signal levels and function I could easily bodge something... :twisted:

Seems like the ultrasonic sensors are a not uncommon fault, if someone has a bit more technical info on the working of the alarm I'll see if I can source some cheaper replacements and / or devise a simple bodge that other forum members could easily do.

An alarm armed with all door sensors active is still better than no alarm at all!
User avatar
Mandrake
Posts: 8438
Joined: 10 Apr 2005, 17:23
x 423

Re: How do I stop the alarm going off Xantia II

Post by Mandrake »

RichardW wrote:There appear to be two types - one with a Diode one without (is that in fact the LED?). Without listed at £33.65, with listed at £96.61 :evil:
Sounds like the part numbers you're looking up include the whole PCB so yes the diode is probably the LED mounted next to the right hand sensor.

I can't see why some naked sensors like the following couldn't be tried, at £5.69 for the pair and a bit of soldering its worth a shot!

http://www.maplin.co.uk/ultrasonic-tran ... 6+Sounders" onclick="window.open(this.href);return false;

Back in NZ I had a bunch of ultrasonic transducers, as long as the size fits they're pretty standard items. I doubt Citroen ones are plated in gold. :lol:
User avatar
reblack68
Posts: 1047
Joined: 11 Feb 2004, 02:28

Re: How do I stop the alarm going off Xantia II

Post by reblack68 »

No car has ever been saved from theft by an alarm, so the best thing to do is lock the car on the key so the alarm isn't set.
User avatar
Mandrake
Posts: 8438
Joined: 10 Apr 2005, 17:23
x 423

Re: How do I stop the alarm going off Xantia II

Post by Mandrake »

Locking the door with the key is inconvenient though, particularly if its raining or you're waiting for someone else to get out of the car before you can leave the door. As I said I'm not that bothered about having a working alarm, I've never had one before, I just want to be able to lock with the remote.

Unfortunately there's no easy way to disable the alarm so that it doesn't arm with the remote, so if that means fixing the alarm or bodging the transducer wiring so that it thinks the transducers are ok, that's what I'll do.

BTW I went and picked up a pair of transducers from maplins and they're a bit too big. #-o That doesn't mean that they won't work or can't be made to fit, I'll find out when I get time to take the mounting strip off the door.
User avatar
CitroJim
A very naughty boy
Posts: 43889
Joined: 30 Apr 2005, 23:33
x 1784

Re: How do I stop the alarm going off Xantia II

Post by CitroJim »

I'm watching with interest Simon... If you can make some generic transducers work than that'll be wonderful...
User avatar
DHallworth
Donor 2016
Posts: 2280
Joined: 20 Nov 2005, 18:05
x 78

Re: How do I stop the alarm going off Xantia II

Post by DHallworth »

I can confirm that just unplugged the ultrasonic sensor is enough to stop the alarm going off without having to press the button.

I had a friend who was having problems with it, Lexia identified that sensor so I thought I'd change it. Unfortunately the sensors I had were from a Series 1 Xantia and his was a Series 2. They were totally different.

I left the sensor unplugged (passengers door in this case) and the alarm hasn't gone off in over 6 months now.

David.
User avatar
Mandrake
Posts: 8438
Joined: 10 Apr 2005, 17:23
x 423

Re: How do I stop the alarm going off Xantia II

Post by Mandrake »

DHallworth wrote:I can confirm that just unplugged the ultrasonic sensor is enough to stop the alarm going off without having to press the button.

I left the sensor unplugged (passengers door in this case) and the alarm hasn't gone off in over 6 months now.
Ah, that's good news David. :) I assume then that the right door sensor beside the light is the "speaker" and the left hand one you disconnected is the "microphone" ? Where is the plug you unplugged, just behind the plastic panel ?

Does the door card have to come off to get access to it ? I tried to pry the small panel off and got the top off but it looks like the bottom peg can't slide out freely while the main door card is in place...so I'm assuming I have to lift up the corner of the door card to get it off completely.

What I might do then is remove both transducers, which will disable the ultrasonic sensor in the mean time (no more pressing the disable button every time) and help me to find a more accurate substitute once I have them in my hands where I can measure and inspect them.

(I can also test them to find what went wrong with them as I have plenty of audio measurement equipment like a proper measurement microphone, audio spectrum analyser software, scope etc, thanks to having speaker building as a hobby :) )
I had a friend who was having problems with it, Lexia identified that sensor so I thought I'd change it. Unfortunately the sensors I had were from a Series 1 Xantia and his was a Series 2. They were totally different.
What's different about them ? The transducer itself or is there a PCB there with different circuitry ?
User avatar
Mandrake
Posts: 8438
Joined: 10 Apr 2005, 17:23
x 423

Re: How do I stop the alarm going off Xantia II

Post by Mandrake »

The L series sensors from Senscomp look very promising:

http://www.senscomp.com/products/piezoe ... p#l_series" onclick="window.open(this.href);return false;

Depending on the exact size of the original which I wont know until I remove it, either the 40LT10 or 40LT12 (and their receiver partners 40LR10 or 40LR12) should do the trick. Looks like all the L series have an operating centre frequency of 40Khz - I'll measure the output driving the transmitter when I remove it to confirm what frequency its using as the transducers won't work properly at the wrong frequency.

Shouldn't be too hard to find some suitable sensors, touch wood. Will keep the forum appraised of my progress. I assume the best way to test they actually work is to leave one window down just enough to get a hand in, arm the alarm, wait a minute or two for the ultrasonic sensors to arm, then wave my arm through the window to set it off ?