Alarm Issues - CLS

[Paul77]

Good morning All,
Having only recently bought my first Mercedes, I am new to the group. Upon the purchase of my car, I wasn't expecting to need to post threads so soon! I currently have 2 areas I would appreciate your help on, and will post in separate threads.
The car first, is a MB CLS Shooting Brake 2.1 2015. I bought at the start of December 2019, and am overall very happy with the car. Very nice to drive, and ticks all the boxes as a family car.
Now for the problem. Whilst sat at home on Friday night, my alarm started going on my car. Following a spate of thefts in the area, I initially thought the car was of course being stolen. After carefully looking over the car, it appeared nothing had been touched, and I locked the car back up. This then happened an additional 4 or 5 times, at about 20-30 minute intervals. The things that stood out to me on the night were that when I approached the alarming car, when I pressed the unlock button on the fob, it unlocked the car, but did not stop the alarm. In fact, I could get in the car and start it whilst the alarm was still going! I've never had a car in the past where it would do this. Normally once you unlock the vehicle, the alarm would stop. But in this instance, it appeared the alarm would go for several minutes before deciding to stop of its own free will. After taking the car for a drive, and re-parking, the alarm stopped going off.
Since Friday night when this happened, when I now park the car, and click the lock button on the fob, the hazards/indicators continue to flash rapidly. This just keeps going, and the only way I can stop it is by pressing the lock button again!
I'll be honest and say I don't really know where to start looking! But am a little concerned as only had the car a month, and now have this problem every time I drive it. I'm hoping it is something you guys recognise and is a simple fix. Just seems odd to start after 1 month of ownership.
Any help or pointers are much appreciated.
Thank you

 

[V6Matty]

This will likely be the battery in the alarm failing, it’s not a known issue on the 218 but was on some other models, the battery leaks onto the board and essentially shorts it out, setting it off. Replacement is the only fix, not expensive or that hard as it’s located in the near side front wheel well.
Welcome to the forum by the way

 

[Paul77]

This will likely be the battery in the alarm failing, it’s not a known issue on the 218 but was on some other models, the battery leaks onto the board and essentially shorts it out, setting it off. Replacement is the only fix, not expensive or that hard as it’s located in the near side front wheel well.
Welcome to the forum by the way

Thank you for the quick response, and welcome. From all that I mentioned, is that what it sounds like to you then? And would that just come on suddenly, like it has?
When you say its in the near side foot well, I assume removal of wheel/tyre? And where will I find it from there? Once located, is it simple to remove the battery and replace?
Thanks again

 

[daibevan]

Did you buy it from a dealer or privately? If a dealer then it's up to them to fix it.

Good luck & welcome. You will get some great advice on here.

 

[mercmancdi]

Hi welcome

 

[EmilysDad]

.... Once located, is it simple to remove the battery and replace?
Thanks again

I think Matty is referring to the alarm siren in which case it's a sealed unit

 

[Paul77]

I think Matty is referring to the alarm siren in which case it's a sealed unit

Thank you for getting involved. Another follow on question, do you mean the battery is a sealed unit? Or the whole alarm siren (with battery inside) is a sealed unit? And is access to this area fairly simple.
Thanks

 

[EmilysDad]

Thank you for getting involved. Another follow on question, do you mean the battery is a sealed unit? Or the whole alarm siren (with battery inside) is a sealed unit? And is access to this area fairly simple.
Thanks

The whole thing is sealed. It'll be something like this .... https://www.ebay.co.uk/itm/Genuine-...721655?hash=item1e924fcab7:g:bwEAAOSw5cNYPalB

I've never looked into where the unit lives, but I'd imagine it's under the plastic wheel arch liner .... set the alarm off & follow the noise .

 

[daibevan]

get a quote from MB Grangemouth. The give a discount if you say you are a member of this forum.

 

[AMGeed]

The alarm siren is around £100 from the dealer (MB Grangemouth is a good call for a discount) and simple to replace once you have removed a wheel and the arch liner closest to the bulkhead. Not sure on a W218 if its the n/sf wheelarch or the o/s/f. Its the o/s/f on a W211
The only tool you need is a security torx bit (T25?, and the one with a small hole in the end) which you can get from Screwfix for very little. https://www.screwfix.com/p/mixed-mixed-security-bit-set-33-pieces/2840v
The torx bit was needed for my W211, so I'm assuming its still needed on a W218? The new siren comes with a standard bolt.
Plug and play, no programming required.

 

[V6Matty]

Thank you for the quick response, and welcome. From all that I mentioned, is that what it sounds like to you then? And would that just come on suddenly, like it has?
When you say its in the near side foot well, I assume removal of wheel/tyre? And where will I find it from there? Once located, is it simple to remove the battery and replace?
Thanks again

Sorry for the late response but looks like the others have pretty much covered your questions. As AMGeed above it’s a simple fix and not too difficult for a home diy’er to complete, just takes a little time.
With your question about it coming on suddenly, yes, they can do. The battery essentially breaks down and then leaks all over the circuit board damaging and shorting it out, I’ve seen a few people repair them but most places charge about £65 and only give a 2year guarantee, for the sake of £30 I’d have a new one which will likely outlast your ownership and may never go wrong again

 

[Phillip Butler]

Good morning All,
Having only recently bought my first Mercedes, I am new to the group. Upon the purchase of my car, I wasn't expecting to need to post threads so soon! I currently have 2 areas I would appreciate your help on, and will post in separate threads.
The car first, is a MB CLS Shooting Brake 2.1 2015. I bought at the start of December 2019, and am overall very happy with the car. Very nice to drive, and ticks all the boxes as a family car.
Now for the problem. Whilst sat at home on Friday night, my alarm started going on my car. Following a spate of thefts in the area, I initially thought the car was of course being stolen. After carefully looking over the car, it appeared nothing had been touched, and I locked the car back up. This then happened an additional 4 or 5 times, at about 20-30 minute intervals. The things that stood out to me on the night were that when I approached the alarming car, when I pressed the unlock button on the fob, it unlocked the car, but did not stop the alarm. In fact, I could get in the car and start it whilst the alarm was still going! I've never had a car in the past where it would do this. Normally once you unlock the vehicle, the alarm would stop. But in this instance, it appeared the alarm would go for several minutes before deciding to stop of its own free will. After taking the car for a drive, and re-parking, the alarm stopped going off.
Since Friday night when this happened, when I now park the car, and click the lock button on the fob, the hazards/indicators continue to flash rapidly. This just keeps going, and the only way I can stop it is by pressing the lock button again!
I'll be honest and say I don't really know where to start looking! But am a little concerned as only had the car a month, and now have this problem every time I drive it. I'm hoping it is something you guys recognise and is a simple fix. Just seems odd to start after 1 month of ownership.
Any help or pointers are much appreciated.
Thank you

I'm also a new member and have had the same problem with my 2016 CLS shooting brake, owned from new. Thanks everyone for the replies.
This is a great forum.

 

[Rob76]

I fitted a new one in my 203 years ago - on the driveway of the dealer: they weren't happy - but it is that simple