Tony Davis

I've just bought a '90 C4 cab fitted with a Sigma M30 alarm. It occasionally goes off 10 minutes or so after I've left the car. If I can get to the car whilst the siren is sounding and press the key fob, the door locking indicators 'settle', the siren stops and I have no more trouble. However after a minute or 2 the siren will stop of its own accord. If I leave it, it will start again later (10 to 20 minutes). If I press the key fob, the doors unlock and the cycle begins again. I've seen the thread from Robert Coats' query. Do my symptoms provide any clues as to where to start fault finding ?

Adrian

Dear Tony,
Sounds like one of your activation switches is breaking contact or the backup battery is playing up (if installed). Now which switch, tough to say. I would start with glove compartment, then doors, rear compartment cover, trunk, engine lid.
Ciao,
Adrian
911C4

PS: It is very important to understand that an alarm system is looking for inputs that change state. This means go from an earth to open. Sensor inputs such as ultrasonic do not work this way, if installed. Loss of electrical power is a change of state.

Tony Davis

Thanks Adrian

A bit more information.

Last night I noticed a whirring noise after I switched off the ignition. It sounded like a low power fan, somewhere behind the dashboard.

This morning I didn't, so set the alarm and it has not gone off in 2 hours. By what you say, an intermittent fault on said 'fan' causing it to stay/come on would be sufficient to trigger the alarm. Any ideas as to what it could be ?

Thanks

Tony

Jeff Curtis

I would certainly suggest that the fan is causing a power drain, which in turn would trigger the alarm.

I too have heard this "whirring" sound from the dashboard after shutting off the car...I've heard that this could be an indication that the climate control panel is going bad?? <img src="confused.gif" border="0">

Adrian

The whirring noise behind the panel after you shut down is standard. Behind the aircon/heating control unit is a temp sensor with its own fan. This remains powered for up to 20 minutes after shutting down. It should run for a maximum 20 minutes. How long it actually runs for is dependent on temp selected and interior temp etc. The whirring noise is dependent upon fan condition more than anything else. A good fan is almost impossible to hear. You will only hear this fan running after the first start of the day. It will not run until you have activated the heating system or cooling system and select a temperature which it can adjust to and are driving along. This means if heating temp requested is higher than ambient or cooling temp is lower than ambient. If you know what I mean. If the fan continues to run for more than 20 minutes then this indicates a bad control unit, because the control unit is not shutting down when it should,
Ciao,
Adrian
911C4

Jeff Curtis

...hence the ~10-20 interval before his alarm goes off again. That is where I was headed with this "diagnosis". Think maybe this is a good place to start - disconnect your climate control for a day, preferably NOT a cold day!

George Stevens

Tony

One of the problems you could be having is that with most alarms when you plip the fob all you are doing is turning the siren off, the reason the alarm sounds again is that it is still on.

You may need to plip it twice, once to turn off the siren and a second time to turn off the actual alarm.

The amount of times the indicators flash should tell you which zone is causing the alarm to go off (this will be expained in the instruction booklet).

Usual problems are faulty microswitches on the front and rear lids and doors or an over sensitive movement detector.

They are a pain mine is forever going off due to an over sensitive movement sensor under the centre consul