W211 Alarm Siren replacement

[Alps]

So whilst getting the car ready for TRAX, the Alarm siren went off whilst i was inside the car.

It sounded distorted and crackly, as per the clip below



Its common for the backup battery to leak and mess up the board inside

Time for a new siren unit, Spoke to my usual parts guy at MB and a new siren and bolt were ordered, cost was just shy of £100 and is an updated part number to what was originally installed.



The siren is located under the drivers side wing, so you need to remove the wheelarch cover nearest to the drivers door, so off comes the wheel


then take off the two plastic pop rivets off the side skirt


then off comes the two 8mm screws from under the arch


Then take off 5 plastic 10mm hex nuts




then pull off the plastic wheelarch liner and put it to one side.

you will then see the siren protective housing


Remove the 3x8mm nuts that hold the housing on
Then remove the plug on the alarm unit itself




the alarm unit itself is held on using a security bolt as per the above pic, a security torq bit will remove this T25 i think was the size.



The alarm unit will then fall out of the housing.

The old and the new alarm sirens are different in physical size as the new one has been updated, the new one uses a 13mm bolt rather than a torx.

Here they are side by side




New siren fitted in housing


here is what the unit looks like when sawn open



The battery had leaked a little other than that all looked ok, but obviously siren itself had seen better days.

This is how the new siren sounds and now beeps when arming and dis-arming - which the old one didn't do.

 

[AMGeed]

Really useful write up. Thanks
Should be a sticky thread.

 

[John]

This is how the new siren sounds and now beeps when arming and dis-arming - which the old one didn't do.

Mine never made a sound arming and disarming since I had it.

The unit worked though because I tried it once as I had no idea what it sounded like which made it hard to know if it was my car going off when they sometimes do.

 

[markjay]

Mine never made a sound arming and disarming since I had it...

Alfie (comandonline.co.uk) reprogrammed mine to omit an audible beep when alarming/disalarming.

It's a STAR twick and the only downside is that the volume can only be adjusted from STAR, so once you set it to the volume level of your choice it stays that way.

Other than that it's a great feature to have...

 

[KillerHERTZ]

IIRC All the replacement ones beep when locking, mine did on my W209 CLK.

I still remember replacing it, getting all the trim off only to discover that I needed a security torx bit, non standard, having to cycle 4 miles in the p!ssing down rain to buy one

 

[Major774]

I prefer the beeps, so I turned it back on using the STAR equipment.

You also get the option of short beeps (US) or long beeps (NL)... I stuck with NL.

Excellent write up as usual Alps

 

[Will]

Good write up Alps

Love the characteristic mirror squeak - 'they all do that'

 

[Gareth]

Cheers Alps, did mine yesterday using this guide.