DIY Mercedes C230 Random False Alarm FIX 

Glad I was able to help you out.

Thanks for sharing, this will be helpful to others looking to perform this fix.

If you remove the fuse your remote wont work anymore.

No, the battery is in the siren!

Yes, its a pretty common issue with these cars. Order a replacement off ebay and fix it yourself. It starts off intermittent and moves to keeping u awake all night long.

james moreno it happened first time a week ago I locked car it went off immediately and I removed rear no5 fuse to do with alarm and rear booth light, checked with sensors eg door/interior but not the issue so I’m assuming the battery in siren leaked onto motherboard

@@fookayou8607 i dont know why Mercedes chose to put the siren in such a low area. Typically when installing aftermarket alarms systems you generally put the sirens high in the engine compartment where its warm and dry. Putting it in an exterior compartment low to the floor is a problem waiting to happen (short).. its pretty easy to extend the wires and mount in a better location if you want to but after performing this fix i haven't had an issue.. then again it hasn't rain so hard here to where the bottom has been submerged in water like it has in the past.

I really appreciate you taking the time to do your video. My cousin cut the cable and moved to Mexico.

Since the body style is the same I'm going to say yes. I would drop the panel and see if the siren is in the same location. If it is then chances are this will work, if you want to get rid of the siren going off, while your in there; just simply unplug the connector to the siren for now until your replacement comes in.

Off ebay, these are called Security torque bits rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.com%2Fulk%2Fitm%2F350583822596

Haven't had a single problem with the alarm since putting this one in. Gone through a few heavy rain storms and flooding and it's holding up like a champ considering it's poor location.

@@TheChemistDIY yup, the location of the alarm is so dumb, idk why mb don't put the alarm in other place, but as i know, the reason of why this alarm die is bcs of the internal battery soldered that corrodes and evenly kills the motherboard. At least, i bought the same model and sounds better than the original alarm.

Christopher Kreschollek , its a hit or miss, in my case no. Its the malfunctioning circuitry on the siren board thats causing the false alarms. Disconnecting that alarm eliminates that issue but also raises another issue. If the alarm no longer sees the siren (open circuit) does that in itself cause a false positive, who to say if this is true because we dont know if the alarm is programmed to do self diagnostic much like how the car tells you when you have a burned out light bulb and reports its location.

Your very welcome, good luck with your fix.

The issue is found in all classes. Tho the location of the horn may be different, the fix is the same from what I've seen..

@@TheChemistDIY omg such a fast reply! Thank you I’ve taken it to garage and they told me initially it was due to the battery. I got that replaced but it’s still happening…. What a waste of money! Think I have to show them your video !

Yeah, the random false alarm is a common issue with Mercedes. Poor location choice and design for an alarm horn that's integrated into the computer system. You can fix this yourself pretty cheap.. just find your siren on the car and pull it.. snap a picture of the backside and find it used on eBay.. I haven't had a problem since..

young king - dont see why Mercedes would change the location but to find out just set off the alarm by opening the door while the system is armed like i demonstrated in the video and listen to where the sound is coming from.

My C230 is an 04 and since I've had it, no it has never chirped when arming or disarming.

The last siren alarm produced for this model make a chirp when You lock and unlock the car, but in the older models(a171 and 203) You need to config the rear Sam to netherlands

But that config disable the panic button

Well technically speaking pulling the 7amp fuse in the trunk should kill the alarm module. But this will also kill other useful features like the remote key entry and maybe even recognization of the key when trying to start the vehicle. If you're looking for an overnight solution then this may be it. Once you return to the vehicle in the morning time or what have you, you will have to reinsert the fuse unless you make some type of on/off switch for that fuse. Of course this would be temporary until you get your new siren. Though I don't know the value of the resistance of the siren, I'm sure adding a resistor (load) in place of the siren in the interim should work as well.. this is a common way to bypass things with most electronic circuits. It's just finding that value. That would keep everything working aside from the malfunctioning siren of course. If you find that value please post it up here so others can do the same.

@@TheChemistDIY what if i disconnect the alarm module itself instead of removing the fuse . I just want to stop the fog light and break light from flashing and draining my battery

Is it compulsary to get a new siren is what i want to know . I am going to test all these tomorrow and will surely get back here

I haven't seen anyone do this. Since the anti-theft system does random checks as in the siren case, It may see the module gone and cause other issues. Maybe that's why no one has posted anything about it.

In order to stop this from happening you need to replace the siren unfortunately. EBay has them pretty cheap and is where I got mine. There is a fix that I have seen on Mercedes-Benz world. It does require you cutting open the siren, cleaning up the circuit board, removing the batteries that are corroded and dead, soldering in some new wires and replacing the dead batteries with two AA batteries for a total of 3.6 volts.

Pretty much going to be the same process. The only difficult part I see is trying to find the location of the siren. Roll down your car windows and arm the alarm system. Then open up your door and listen where the sound is coming from from the siren. Mercedes has a bad habit of putting these in the fender wells either on the driver side or passenger side. But this method should tell you if it's still functional. Once you find and remove, look at the plug and see the shape and number of pins then Jump on ebay and find a used one.

@@TheChemistDIY had the car diagnosed at Mercedes dealer and they are saying the Rear SAM needs to be replaced. Said that’s causing my overnight power drain.

@@BOSSASSNIGG www.mercedesmedic.com/mercedes-sam-module/#:~:text=A%20SAM%20module%20(also%20called,modules%20since%20the%20mid%2D90s.

Dude thats crazy, glad to see ur ok bro. you got full coverage, if so thats an easy fix.

Yeah i have insurance here in the uk if its someone else fault, their insurance pays for it. Bike is a mess right now. but i will fix it

Sorry Derrick, i made this video such a long time ago i dont recall the name, title or even where i got the song from.

Did you check the fuses, both driver side under the hood and the ones located on the driver side door dash location.

@@TheChemistDIY Hello and thanks for your reply. No I didn’t, but I drove the car like a month a go and everything was good. New battery. Today this alarm started to go off out of nowhere... My keyfob light up but it don’t lock or unlock the car, nor when I turn to turn car on I can’t turn key. Can this alarm cause this to happen? To shut everything down? Maybe my battery just died? I try to jump it and nothing

@@sleepdoctor3433 Ok so with that new information - In your trunk, there is a fuse box on the driver's side. Check the number #8 fuse I believe it is. Should be like 7.5 or 10 amp fuse if memory serves correctly. This fuse is related to the siren horn and antitheft system. Since the horn is in the worst place to put it (outside and under the car).. sometimes when you drive through a large puddle the siren will get wet and cause this fuse to pop due to electrical short. Let me know if this fixes your issue.. If not your not going to like the next bit of information I'm going to give you.

@@TheChemistDIY Hello I forgot to say I found and removed the siren and reconnected the battery and still no power or even able to turn key in ignition

And you checked the trunk fuse as I stated before? When you say no power.. are meaning that the whole car has no power? If so then this should be the main fuse.. if you enter the vehicle and the cluster lights up then you have power to the vehicle and the issue is going to be the anti-theft system.. What you are referring to as the alarm is not really an alarm. An alarm is what you buy from your mom and pop store on the corner. The Mercedes has an anti-theft system which immobilizes the entire vehicle. This begins with your key fob, doors, engine start. These are all modules within the main system and cannot be repaired by you. If it is your anti-theft system then you will need to have the vehicle towed to the dealership in order to repair because they need to put it on their computer system to figure out which module has gone bad.

rbu2m-dont quote me on this but this may be because the circuitry within the alarm provides a load balance check. If the alarm brain dose not see a responce signal it thinks the circut is open their for triggering the alert (siren, flashing lights). All you have simply done is stopped the audible portion of the alarm, in essence your still in the same boat, the circut is still open as it was when it broke, does that make sense???

Thanks for the information, I think I might have bad short some where that causes the alarm to go off. It does not goes off that often. but when it does I just unlock the doors and re-lock it again and it is good to go. But seems every time the right rear door is use the alarm started to acts up.

rbu2m - Good to know, you may want to test the door plunger. remove it from the vehicle and run a continuity check as you press and depress the plunger. It might be time for a new one. you may also want to spray some contact cleaner in them all. this may help with any corrosion that has built up over the years on each one. I like to go with least expensive methods first before making a big investment like taking it to the dealership.

Sounds good.Thanks

Unfortunately the only way to silence the alarm is to disconnect the connector at the siren, or at least that's the way it worked for me. The alarm itself will continue to produce false alarms until replacement thus causing the light to flash but with no audible ton. You want to make sure you fixed this fast because an alarm going off throughtout the night will definitely lead to a dead car battery the next morning depending on the state of your battery. The batteries that I speak of in the video that go dead are the ones within the siren housing, I'm not sure why batteries are needed as typical car alarms sirens dont have these. Perhaps it to send back a pulse to the alarm brain to inform the brain unit of proper functioning.. who knows. Like most batteries that deal with the outside elements it will sulfate around exposed areas and end up destroying itself through corrosion.. that's why it looks the way it does in the video. The sooner you get the replacement the better.

james moreno such a fast response ! Thanks ! I had a mechanic Replace the unit about six months ago ( he seems to be unreachable these last few days ) he told me the separate batteries are necessary so that if a thief disables the battery the alarm will still work. I am going to offer up a guess that the batteries work in tandem to a degree and that if the main battery gets low ( as mine dies as it is a low mileage use second car ) that it might effect that voltage needed to maintain the alarm signal back and forth. It is a shot for now I guess and so I put a battery charger on the main battery all day today. I guess one way to test that theory is to disconnect the main battery when the problem is happening and see if it stops the alarm ! For now ... since the alarm tends to go off in the middle of the night waking me and the neighbors… Is that I have found the only cure is to put the key in the ignition and put the driver window down so that I don’t get locked out if something automatically locks and I don’t have a second key. Of course this is just a desperate temporary measure. And as a safety measure I block the Mercedes in with my other car so it can’t be stolen. Any feedback appreciated. Again thanks for your quick response.

@@funguy4utube not that I ever tried but you want to consider.. see if theres a fuse for the alarm that you can pull. Take a look at the link below and let me know if you find and the result. I'll make it sticky for others to see and share. mbworld.org/forums/sl-class-r230/297359-how-diable-alarm-keep-going-not-just-turning-off-silence-2.html

james moreno fuse ! Great idea ... I will check that out and post the results. I kept this car for sentimental reasons and don’t want to spend any more on it. I have spent over 12k fixing it up and it is only valued at around 2k - so my fixed are reduced to bare minimum ways. Thanks so much ! Btw ... I full charged the main battery yesterday and the alarm still went off for no reason - so charging the main battery has no effect on the random alarms.

@@funguy4utube sentimental value, ya I hear ya. I still have my 04 and it has over 200k on the clock and it looks just as good if not better then the first day I bought it with all the other stuff I've added like rim's and a TV/audio system that I added in my younger years, I get complemented on it quite often. I purchased the car in my late 20s after my parents told me I couldnt afford this type of vehicle, I guess to me it was a testament to prove a point to my parents never doubt my capabilities as young adult..almost 50 now I still have the car and it runs and looks great with minor issue hear and there. Yes repairs are pricey when comes to jobs above my tools, space and time limits but for the smaller stuff (which is still pricey) this only forced me to learn how to work on it myself which to me is invaluable. To date I've fixed such things as breaks/rotors, abs system modules, catalytic, exhaust header gaskets, cam sensors, MAFs, throttle bodies, shocks/struts, vacuum system and hoses, clear error codes, electrical switches and the list goes on and on.. but with all that said the car still great and has out lived any other vehicle I've had in the past. It was a great purchase and i may turn it over to my 17 year old boy as his first car in his senior year of high school. Definitely keep me posted on your findings. It only adds to my knowledge of the vehicle should this issue occur again and help others out as well.

Not sure if I'm following you brother.. this video shows how to disconnect the malfunctioning siren temporarily causing false alarms till you find a replacement as I did.