TheEnd
Member
Recently I've had a few issues where instead of the 3 flashes on locking (and chirps in my case) I have been getting one flash (and chirp), a brief pause, and then fast flashing of the indicators, usually followed by the alarm going off.
This is a symptom of the internal batteries having issues, either dead, leaking or both. Replacements can be bought and fitted, no coding required, but if they are used, they might not have much life left in them.
What I decided to do was get inside the siren unit and see what could be done.
The siren on my W211 was behind the driver's side arch liner. I believe some models may have it on the passenger side, so if it does go off, you can listen to see where it is first.
You'll need to start with taking the wheel off, jacking the car, and getting the rear section of arch liner out of the way. There's 4 10mm plastic nuts, 2 8mm bolts at the bottom rear edge going directly up into the undertray, and 2 press stud expanding rivets that lock into the sideskirt. A bit of pulling at this will get the liner moved.
The siren/sounder is in the metal box, 3 8mm nuts holding the bracket to the chassis.
Once this is undone, you can get a bit more working space, often having to cut a tie wrap and then unbolt the siren from the frame. I had a T40 security Torx, I have heard of other types of bolt being used too.
Next is to cut it open, it is sealed so I went around the middle seam with a dremel to separate the casing. The rear part will lift up, and the connection pins will be unharmed and remain on the circuit board
The dark green discolouration is from the batteries leaking. Hopefully everything will still be surviving if you catch it early enough.
You can see a little bend in one of the connector pins, a gentle nudge back into line sorts that out.
With the old batteries cut out, the PCB can be cleaned up
Some of the corrosion did make its way through to the other side, but hasn't seemed to have done any major damage yet.
The battery type is a Varta 3/V150H, which means a pack of 3 of these specific type. I bought mine through Farnell, googling 3/V150H does bring them up from a lot of different sellers. The original Mercedes one have 4 legs, the ones I got had 3 legs on them. If you can find 4 legs, certainly go for them, ones without any legs are best avoided as soldering onto a battery is very tricky. The majority of battery connections are made by spot welds instead of soldering.
Two of the legs fit perfectly, for the last leg, I made a couple of copper wire "goal posts" which were soldering into the existing holes, and then the final leg folded around this with a dab of solder to make a permanent connection.
Once all done, the case can be put back together, and then sealed up. I used black silicone in the gap from the dremel cut, and wrapped tightly in tape and left overnight to cure.
Once it had all gone off, it's ready to go back on the car, and everything is now back to normal.
The original batteries were showing 1.2v on one, and 0v on the other so that was the main issue.
Batteries are about £6 each, so with a bit of time taken, an existing siren might be able to be repaired for about £12 and some silicone.
This is a symptom of the internal batteries having issues, either dead, leaking or both. Replacements can be bought and fitted, no coding required, but if they are used, they might not have much life left in them.
What I decided to do was get inside the siren unit and see what could be done.
The siren on my W211 was behind the driver's side arch liner. I believe some models may have it on the passenger side, so if it does go off, you can listen to see where it is first.
You'll need to start with taking the wheel off, jacking the car, and getting the rear section of arch liner out of the way. There's 4 10mm plastic nuts, 2 8mm bolts at the bottom rear edge going directly up into the undertray, and 2 press stud expanding rivets that lock into the sideskirt. A bit of pulling at this will get the liner moved.
The siren/sounder is in the metal box, 3 8mm nuts holding the bracket to the chassis.
Once this is undone, you can get a bit more working space, often having to cut a tie wrap and then unbolt the siren from the frame. I had a T40 security Torx, I have heard of other types of bolt being used too.
Next is to cut it open, it is sealed so I went around the middle seam with a dremel to separate the casing. The rear part will lift up, and the connection pins will be unharmed and remain on the circuit board
The dark green discolouration is from the batteries leaking. Hopefully everything will still be surviving if you catch it early enough.
You can see a little bend in one of the connector pins, a gentle nudge back into line sorts that out.
With the old batteries cut out, the PCB can be cleaned up
Some of the corrosion did make its way through to the other side, but hasn't seemed to have done any major damage yet.
The battery type is a Varta 3/V150H, which means a pack of 3 of these specific type. I bought mine through Farnell, googling 3/V150H does bring them up from a lot of different sellers. The original Mercedes one have 4 legs, the ones I got had 3 legs on them. If you can find 4 legs, certainly go for them, ones without any legs are best avoided as soldering onto a battery is very tricky. The majority of battery connections are made by spot welds instead of soldering.
Two of the legs fit perfectly, for the last leg, I made a couple of copper wire "goal posts" which were soldering into the existing holes, and then the final leg folded around this with a dab of solder to make a permanent connection.
Once all done, the case can be put back together, and then sealed up. I used black silicone in the gap from the dremel cut, and wrapped tightly in tape and left overnight to cure.
Once it had all gone off, it's ready to go back on the car, and everything is now back to normal.
The original batteries were showing 1.2v on one, and 0v on the other so that was the main issue.
Batteries are about £6 each, so with a bit of time taken, an existing siren might be able to be repaired for about £12 and some silicone.
