Alarm/ Deadlocking, Phantom Triggering

The alarm system on my S2 V6 has been driving me to distraction ever since I bought the car in April. It randomly triggers for no apparent reason, so much so that I no longer use the alarm/ deadlocking facility.

It has done it ever since the first night with the car. I have had several attempts at fault finding the alarm, to no avail. Several of the fixes seemed so likely to be the solution, but no, the alarm still triggers.

The first fault was found by accident. One of the minor niggly faults on the car was that the door open display didn't work on the rear driverside door. After recieving noz's manual on disk I decided to have a go. The switch is built in to the door lock mechanism, so that an alarm is given even if the door is on the first catch. I disconnected the door at the door post plug/socket and applied an earth with a test clip. The display worked. Fault proved to door. When testing in to the door with a meter I could see open circuit when the door catch was set to locked, and many meg ohms when the door catch was opened. I wrongly assumed that it was the switch on the door lock and proceeded to remove the lock. Its a bit of a pain because the door is lined by a sound deadening, draught proofing and water proof membrane. This can be peeled back with out doing any damage if it is done firmly but gently with the help of a hot air gun.

With the lock removed, it was tested directly into the switch contacts, and it worked perfectly. The lock was reinstalled and the search began for a fault in the loom. Luckily I didn't have to look far. Where the loom passed through the door frame to the lock the insulation had been snagged. Corrosion due to current flowing from the cable to the earthed door during damp conditions had dissolved the copper about half an inch back up the wire sheath. I trimmed the wires back, slipped over a piece of heatshrink sleeve and the soldered the stripped ends together. Then the sleeve was shrunk. The door switch worked normaly again.

It dawned on me, after looking at the alarm wiring that the alarm worked off the same switch. So I assumed I had solved the alarm problem as well, that leakage current had been triggering the alarm.

Wrong! The damn thing still went off.

Thinking I was on the right path, I tested all the door switches, boot and bonnet aginst the mimic warning lights, and lo and behold, the bonnet warning didn't work either. After removing the front grill, the switches are mounted on the bonnet catches. Both were a green corroded mess. Again, suspects I, leakage currents during wet periods trigger the alarm. The switches were disconnected and removed and the connectors bagged up to keep them dry. The alarm didn't trigger over the next few days, so I ordered new switches. £16 each.

However! Before the new switches arrived, the alarms started again. Now I'm stuck for ideas.

I've tried disabling the ultrasonic detectors, but it still triggers. The only thing I can think of now is that another door may be getting leaky, or the alarm has a volt-drop detector that triggers if an electrical load is switched on, that may be miss triggering. To be able to test back in to the wiring in more depth I need to get to the alarm unit, but I belive it is buried behind the instrument cluster.

Has anybody any further ideas before I start ripping the dash apart?

Ian

Just a thought, it couldn't be a fault on your key fob transmitter could it?

Peter.N.

i had the same sort of problem on my mk2 i found that the fix of sorts was switch the in car sensors off but it now is fine guess it fixed its self by being used more sorry to read you have tried this with no affect. also have a look at the fuse box in the engine bay, a friend found this to be the fix for his but your not looking for a blown fuse but a over heated fuse normaly the center fuse in the first row
yours Craig

This post has been edited by Craigdp on December 30, 2005 03:14 am

Hi Peter,

I discounted the fob as the 'Plip' connects directly with the central locking system. The signals to arm and disarm the alarm are 'forwarded' from the central locking controller. The central locking works fine every time without fail.

Hi Craig,

I supose a loose fuse could easily be a cause. If the alarm has a voltage sensor, a lot have to trigger if a load like a boot light suddenly comes on, then an intermittant fault like that could trigger it. Likewise a fault causing the cooling fans to come on or similar.

I notice that the alarm has a diagnostic pin to the diagnostic connector. Any body have any info on this?

Hi Ian

I just wondered if the plip was sending out intermittent unrequested spurious signals, or do you have to lock it with the other button first? I should know I've got one! Only TV remote controls sometimes do this, and I have spent ages trying to find a fault which has dissapeared when I have taken the batteries out or removed the control to another room.

Peter.N.

Hi All

Just to mention that the Mk2 plip "A" button sends out its code on two different frequencies and the receiver on the car expects these frequencies to alternate with each signal accepted. The plip is programmed to alternate frequencies with each press of the "A" button. If the same signal is sent a second time the receiver just ignores it, the plip rotates its code with each press and on next press the signal is accepted. If you have 2 plips and the other one is used there is a 50/50 chance you will need to press twice to get the car to respond. If you open a door between locking with the plip and deadlocking the door open sensor sends a message and the remote receiver alternates to the next frequency and gets out of sync with the plip. This then requires a further press of the "A" button to re establish frequency sync.

I only found this out because I tried a 3 button plip with separate door unlock and door lock buttons as well as the dead lock button. With this plip I was able to transmit all 3 frequencies in any sequence. If I opened the door during the locking sequence the door lock and door unlock buttons transposed. I spent a happy 3 hours or so experimenting (with the windows down in case I dead locked myself in) until it dawned on me that the "A" button of the real plip transmitted a rolling code of two seperate frequencies. Plip rolling code was something that the technician at a dealer had mentioned while he was cutting some new fob keys for me but was unable to explain what it was other than an additional anti theft feature.

From about 1997 onwards the remote receiver on the car has an extra wire that sends a signal to unlock the keypad when the plip is used to open the car.

Not sure that any of this helps with the original problem but it might give a few extra malfunction options for items that are not covered very well in even the workshop manual. I think it also means that the plip batteries need replacing well before they are flat to keep the system working properly.

Regards

XMexc

Just reading through the 'Evolution' notes in Noz's manual, I noticed that there is a paragraph that mentions that transmitter and reciever may get unsynchronised and stop working. To resynchronise the units the ignition should be switched on and then one of the remote buttons pressed for at least 1 second to resync the radios.

It also says that the ultrasonic inhibit button can be used to inhibit the sounder when the alarm is set. Again with the ignition switched on, press and hold the button for a minimum of five seconds, after which the red led in the dash should flicker rapidly. Switch off the ignition and lock and set the alarm as normal, the car is then alarmed, but the sounder will not sound if triggered. I tried this last night and it worked. The alarm went off about an hour after setting it, flashed lights but no sounder. At least I can continue fault finding without waking the neighbors.

I've never had the plips go out of sync though.

sorry, that last post was by me, I forgot to log in

Well! you learn something new everyday. In 10 years and about 250k miles of XM ownership, I didn't know that.

Peter.N.

well you learn something new every day i have to use the key in the engine bay to switch mine off. you could always unplug the sounder not a cure for the problem
p.s. does anyone eles alarm go beep if you activate it with the boot open

This post has been edited by Craigdp on January 01, 2006 07:48 pm

Mine won't turn on with the doors open. I inadvertantly left one of the rear doors one click open the other day and it locked, but the alarm wouldn't turn on. I assumed it was the same for the tailgate. Could have bleeped, I was outside the car though.......

Hi All

The locking and the deadlocking on a Mk2 from the plip are two separate actions.
The car locks on the first press of the "A" button. This should lock all 5 doors. When the "B" button is then pressed the deadlocks will operate but if any door has not locked or its sensor says that it is open then the deadlocks spring back with a loud noise. The indicators should also flash and the alarm hoot. This is to warn someone locking the car while walking away from it that the car has not locked
properly.

False alarm activations can come from wind gusts from a window or sun roof just ajar, though I doubt that anyone has this problem with the present weather.
A while ago I suffered a number of unexplained alarm activations while parked up on the front drive. Eventually realised it was in industrious money spider using the mirror to drop from.

Regards

XMexc

"industrious money spider using the mirror to drop from."

Show how sensiative they can be, i have spiders in the wing mirrors of the XM but no alarm going off and mice under the bonnet of the 2cv (no hold on thats what powers it)

Hi All

Most of us with Mk2's have the earlier ones with the alarm disable switch under the bonnet. By the 1997 model or so the alarm system had moved a step forward (more integrated) and the manual under bonnet switch was removed and replaced by a sequence of actions. It seems to me that the original questioner is fighting to make this newer system work correctly while we just turn off our wayward alarm systems.

Now as to mice under the bonnet! I blame them for rusting my strut head tops by widdling on them.

Regards

XMexc

I had this problem too. I even fitted little clear plastic discs over the sensors on the dash. It helped a lot but I still ended up turning off the sounder under the bonnet. The hot fuses under the bonnet seem to cause many faults that don't seem to be connected so I wouldn't be surprised if they were part of the issue.