Alarm goes off when unlocking

[markross]

A few weeks ago my alarm started going off when I unlocked the car with the remote fob. It only seemed to happen when the car had been left a while, for example it went off every morning but not during the day. Recently it seems to have got worse - it now goes off during the day if it has been left a few hours. The alarm goes off for between 5 and 15 beeps generally. The longer it's been left, the longer it seems to be before it disengages. Any idea what's causing this and how it could be fixed?

Cheers

Mark

 

[markross]

The problem was getting worse and worse - sometimes going off for over 5 minutes when unlocking the car in the morning. It seemed to be worse when the weather was cold. I've taken it to a garage and they've had it 4 days now, and have tried a new siren and new sensor. Now they think it may be something wrong with the wiring. I'm not convinced they know what they are doing - shouldn't a competent garage have been able to diagnose and fix the problem straight away? The bill is running at nearly £300 so far. Should I leave it with them or give up and take it somewhere else? This is starting to really frustrate me!

 

[markross]

I suspect a search on the forum will bring the answer but my first two suggestions would be either your battery isn't holding charge or the infamaous central convenience unit is on its way out...

Do you mean the battery in the alarm? The siren only goes off when unlocking. If the battery in the alarm wasn't holding charge wouldnt the siren go off randomly? It only happens when I first unlock the car.

 

[riverlad]

I assume UPL means the main car battery. I don't think the alarm has its own.

What age is your car? Could be the origonal one so could be on its way out.

If it is your central conveniance unit, there is a chap in the german club who can repair them. I beleve there is a loan unit in the uk to use when yours is sent away to be repaired.

Cheers

David

 

[spike]

Do you mean the battery in the alarm? The siren only goes off when unlocking. If the battery in the alarm wasn't holding charge wouldnt the siren go off randomly? It only happens when I first unlock the car.

It could be a faulty door lock microswitch. I had a similar problem with the boot lock which triggered the alarm after a few seconds if the boot was opened first.
Try opening one of the other doors first to see if it makes any difference. Also check the flash sequence of the LED on the drivers door when locking the car - the attached post gives more details - http://www.a2oc.net/forum/showpost.php?p=102152&postcount=4
It refers to the service flap but applies to any incorrect door / flap locking fault.

For info, the alarm siren does have a built-in back-up battery which is not replaceable. The main battery could also trigger the alarm if in poor condition. In cold weather the voltage may just dip enough at night to trigger the alarm.

Cheers Spike

 

[markross]

Thanks for all your responses so far. The garage now has it in for the 7th day and are checking the continuity of the wiring. Surely it can't be that? Spike in response to your suggestion:

Try opening one of the other doors first to see if it makes any difference. Also check the flash sequence of the LED on the drivers door when locking the car - the attached post gives more details - http://www.a2oc.net/forum/showpost.php?p=102152&postcount=4
Cheers Spike

... the alarm goes off as soon as I unlock the car using the remote, not when opening the door. So do you think it could still be related to a microswitch?

The garage haven't mentioned the central convenience unit or main battery yet. Could it be that they don't really know what they are doing? Do you think I should just tell them not to bother and take it elsewhere?

 

[spike]

... the alarm goes off as soon as I unlock the car using the remote, not when opening the door. So do you think it could still be related to a microswitch?

Not 100% sure but I don't think it could be a microswitch.
Did the garage do a diagnostic scan ?
These are just wild guesses but things I would experiment with are -
Use the door pillar button to disable the interior monitor then see if the alarm still goes off when the car is unlocked.

Cheers Spike

 

[markross]

Not 100% sure but I don't think it could be a microswitch.
Did the garage do a diagnostic scan ?
These are just wild guesses but things I would experiment with are -
Use the door pillar button to disable the interior monitor then see if the alarm still goes off when the car is unlocked.

Cheers Spike

Yes the garage say they've have done a diagnostic scan and it's showing various faults with the alarm (including the siren) which is why they initially replaced it. I tried the door pillar button and it still goes off. However I've just discovered that using the physical key (rather than remote) to unlock doesn't cause the alarm to go off.

I've also noticed that when it goes off after using the remote, it's only the siren - the hazards don't flash which is usual when alarm goes off normally isn't it?

 

[markross]

Just an update on this (as it always annoys me when solutions aren't posted on threads like this) - it did turn out to be the conveniance unit unfortunately - ended up costing me £470 in total. Not very happy but at least it's now fixed.