Alarm help!

[Cwatters84]

hi all, having a problem with my cls 320 alarm. Twice over the last couple of weeks the alarm has started going off for no reason. Last night I unlocked and locked the car after it went off and it kept going off 4 or 5 times. I’ve read posts about people saying it’s a common fault for the bonnet catch to play up but it would usaully come up on my dash if the bonnet wasn’t closed so don’t think it’s this.
Another fault people are saying is the siren itself, the batteries inside can corrode and leak over time causing the alarm to go off. I’ve seen videos how to remove the siren. If it is this and I just take the siren out for a short term fix, I’m guessing the hazards will still flash when the alarm is going off but there will be no sound! Flashing lights will annoy the neighbours but better than the siren going off! Anybody else had this problem and how did you over come it?

 

[Dec]

What year is car?

Dec

 

[Cwatters84]

It’s a 2007, w219 I believe

 

[Dec]

Most likely the alarm siren becoming corrupt, unlikely to be the bonnet switch.

However, if your car battery is in poor condition and not holding a charge, sometimes a sudden voltage drop can trigger the alarm as it might thing it is being tamper with ( as in a thief cutting wires), if you feel the car battery is good then its likely the siren has becoming faulty.


Examples… mercedes alarm siren pcb - Google Search


Dec

 

[Cwatters84]

Ok thanks that was what I was thinking. New sirens are around £100 I think.
So if I was to remove the original one for the time being so it doesn’t keep going off, the car would still be fully usable and wouldn’t play up with the electrics?

 

[Dec]

With Mercedes electrics, nothing is for sure, be sure the car is unlocked before you remove the siren so that it is disarmed. It should function as normal without the siren. No alarm – no theft insurance cover.

The siren rechargeable batteries are still capable of powering the siren until the are depleted so you will need to remove the siren from the car to prevent further false alarms.


Dec

 

[rf065]

Not sure if this is relavent in your case, but our SLC300 alarm randomly went off 5 or 6 times a few weeks ago, always late evening or early hours of the morning. The wife found a spider in the car one day & removed it, the alarm has not went off since!

 

[Cwatters84]

Thanks for your advice dec.
Rf065, this did cross my mind as it is the season for spiders to be coming inside! Where are the interior sensors on a w219? The actual sensors not the button to turn them off