According to the dogs in the street, the designers at Mercedes decided it was unbecoming for any Mercedes-Benz to be heard beeping in public so the decided to turn off the locking beeps, the beeps come from the car alarm siren.
Your car is likely to have the beeps disabled, I don’t think the beeps can be turned on in the menus of your car but may be wrong about that. 'audio off' might mean the radio?
If you need to buy a new siren, take your VIN to the dealer and the will supply the correct siren for your car. If you fit it yourself then it will beep when locking.
https://www.youtube.com/watch?v=ro2GrvpIsus
[YOUTUBE]ro2GrvpIsus[/YOUTUBE]
The Mercedes alarm siren contains the alarm brain and has rechargeable batteries inside, eventually, at around 10 years of age, the rechargeable batteries start to corrode and short circuit, the PCB may become damaged, causing problems like false alarms, battery drains and other odd faults, perhaps your mystery locking problem was caused by a failing alarm siren.
Its best to test the alarm regularly by triggering it, when triggered, it should flash the hazards for 3 minutes and sound the siren for 30 seconds, after 3 minutes it should reset itself.
See also… http://www.mbclub.co.uk/forums/electronics/214758-w211-alarm-siren-replacement.html
https://www.youtube.com/watch?v=BzmpeK1TFfw
[YOUTUBE]BzmpeK1TFfw[/YOUTUBE]
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