Alarm Fault Keeps Going Off

Hi all,
I need your help please its making my head hurt trying to solve this issue with the alarm,
I have a C3 2010 A51 Model, ive had it for nearly four years, without any issues other than the norm servicing etc.

A few months back the Wiper Arms would not return to start position and would randomly stutter and stall halfway across the windscreen, now before this occurred i could hear water swishing about behind the dashboard , upon inspection the water scuttle box had at least 2 litres of water in it! i removed the wiper motor and arms so i could clear the blockage and let it drain out, it appears that the wiper motor had been sitting in water for quite a while and so i thought this was the cause of the wiper fault issues.

Then economy mode was displayed on dashboard !!!!!
I had not used the car for a number of weeks during lockdown so,
I replaced the battery that sorted that issue out.

Alarm is now randomly going off! the alarm is sounding but indicators are not flashing and wont turn off with keyfob,
i noticed when the car was running that the red interior sensor switch was illuminated constantly,
so i checked all the sensors for bonnet , doors, boot, interior sensors, all are working fine and alarm works with indicators flashing and turns off with keyfob.

I then took out the alarm siren unit a Delphi, opened it up as i found out they have a built in battery backup and after 10 years , the battery was fully charged and seemed fine, but i ordered another siren unit off a 3 year old DS3 , fitted alarm works fine.

But!! again its doing this random going off , sometimes for eleven times in a row other times singular,

all i can think of is that water has got into the main alarm module unit , but ive looked everywhere and cant find it, took lower dash off drivers side nothing , took lower dash passenger side nothing ,

Anyone know where its located? i checked where its located on a mk1 C3 but not in the same location on a mk2 , then wiring diagram states behind drivers side dash !

• Where is it located?
  what is causing this issue?
  is it a common fault?
  help me please

best regards

Martin

Hi Martin

If you found the siren, look on the opposite side of the car, in the same position for the alarm module.

It probably got wet too.

Not a common problem for it to fail, but getting it wet will kill it.

Programmed to the car, not a cheap fix.

This is the diagram I have for the C3 A51 siren and alarm locations



1 is the alarm ECU

The ECU appears to be behind the glove box and on the firewall, inside the cabin, by the look of the illustration. As you know the ECU for the Mk1 and Mk2 it’s in the driver’s side kick panel.
The electrical connector for the siren may have corrosion from water. The bonnet switch and the siren are the two I would suspect. The rest of the items in the system are inside the cabin and not exposed to the environment.
If the door switches failed you would get the interior light on and a warning on the central display. If the volumetric sensors failed they simply wouldn’t detect movement in the cabin. I doubt they would cause a false trigger if they were faulty but see below. Could there be something moving in the car to set off the volumetric sensors? I do not know if your ECU has a “bump” sensor. It’s a sensor to detect if the car has been tilted or hit. It might be over sensitive but I doubt it. That sensor is part of the ECU.
If the system is armed and the siren is disconnected the siren will go off. If there is a bad connection at the siren the siren will go off. It will think someone is trying to disconnect the siren. That’s why there is a battery in the siren. It will continue to run even if physically removed from the car. If the system is armed and the CAR battery is disconnected the siren will go off.
You can disconnect the siren (with the system off) and see if the alarm light comes on later (false trigger). This will tell you if the fault is in another part if the system. Of course the siren won’t go off because it’s not connected.
You can try disconnecting the bonnet switch. If the switch is faulty the alarm won’t be falsely triggered with the switch removed. Again if the alarm goes off the problem is somewhere else. The “bonnet open” indication on the central display comes from the alarm module. The bonnet switch is connected to the alarm and not the BSI. That’s why you don’t get a bonnet indication on a car without an alarm.
If you can find the ECU you can try disconnecting the volumetric sensors for the same reason.
The alarm module is about 100mmX50mmX40mm, is black and has one brown connector going to the volumetric sensors and a blue connector going to the vehicle wiring loom.
The alarm modules are not coded to the car. However like a lot of stuff there are CAN and VAN versions. Yours will be CAN BUS.
I don’t believe the hazard lights flash when the alarm goes off but I’m not sure. However if they ARE supposed to flash AND they don’t during a false trigger event, then that points to the siren going off by itself and not the alarm triggering it. Also, you said the siren wont stop when you press the plip. Do the hazards flash when you hit the plip and the alarm has false triggered? Again if the hazards flash but the alarm fails to shut off it points to the siren. Does the siren stop if you start the ignition?

Hi all,

thankyou first of all for your help and guidance,

unfortunately i still can not find the alarm ecu , ive had the glove box completely removed cant see it, checked around the fuse box,
ive took drivers side lower dash , also tried to follow the wiring from interior sonic sensor overide switch, seems to run to the left towards passenger side!! grrrrrr , i removed radio just in case it was behind there nope!
inside the engine bay, scuttlebox has wiper motor and linkages drivers side, and alarm siren unit passenger side,
im at a loss where it is, it must exist as ive had it put on a testing diagnosis kit and it had registered a long list of breakins from all the sensors, so its somewhere in the car ,

ive emailed loads of people off Ebay selling the alarm module but they cant remember where its located or im told its driver side above pedals even though ive expressed thats on a mk 1 citroen c3.

any further advice greatly appreciated,

al the best

Jason

Arfur Dent wrote: ↑Wed Jul 01, 2020 5:03 pm This is the diagram I have for the C3 A51 siren and alarm locations






1 is the alarm ECU

Did the diagram not help?

Arfur Dent wrote: ↑Wed Jul 01, 2020 5:03 pm

Did the diagram not help?

Thanks for the diagram, i can find the siren unit thats found in the scuttle box passenger side, but drivers side in scuttle box is just wiper motor and arms, ive removed both these,
the diagram is for a LHD vehicle so id of thought it would be opposite for RHD ?
If the water was in the scuttle box drivers side, and wet the wiper motor, im guessing if water has got into the alarm ecu then it must be located drivers side, inside the car, at the level the diagram shows it must be behind the dash near the windscreen,
any thoughts appreciated.

thanks

Hi

Citroen don't swap parts over for LHD or RHD, generally its only the steering wheel etc. Even the RHD brake pedal is just an extension of the LHD design.

All ECUs are in the same places LHD/RHD.