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Pete, Mercedes Mechanic
Category: Mercedes
Satisfied Customers: 28717
Experience:  Over 15 years experience as a Mercedes dealer technician
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I have a 2010 cls550. I wasn't driving it much so the

Customer Question

I have a 2010 cls550. I wasn't driving it much so the battery started draining. And then I got the "Device unavailable" message for Radio and no sound from the speakers for any functionality like phone, cd, etc...
All fuses are ok. I opened the command unit and the optical connector on the amplifier in the trunk. Shone light through so can see the light coming out of one of the optical but not the other.
Is there a component in between the amp and command on the optical line that has no light passing through or the line got pinched.
What is draining the battery? I disconnected the command power but it still drained the battery. Now I have disconnected the amp and will check in a couple of hours if the battery is draining or not.
Submitted: 1 year ago.
Category: Mercedes
Expert:  Pete replied 1 year ago.

Hi my name is ***** ***** I will be happy to assist with this today.In some cases I may need more info to assist better.I apologize for any delay.

Have you recharged the battery at all or ran and drove the vehicle quite a bit since this message started?

Let me know so we can continue,thanks Pete.

Customer: replied 1 year ago.
I have been charging the battery fully with an external charger.
Customer: replied 1 year ago.
I have been driving the vehicle now and do disconnect the battery when I am not driving it. It drains down in a day where it will not start so I disconnect if I am not going to drive more than a day
Customer: replied 1 year ago.
This started a couple of months ago. and I have been driving and disconnecting the battery when not driving more than a day. Everything seems to be ok with that. It is just that there is some component on the optic fibre that is drainging the battery.
Customer: replied 1 year ago.
I have lifter the back seat also and see the fibre optic cable going through this area. Is there any component between here to the Alpine command module? Is the satellite radio part of alpine module or is it separate if so where is it located?
Expert:  Pete replied 1 year ago.

I apologize for the slight delay.

O.k.,it does sound like you have a battery drain/draw issue and this can be on the fiber optic side with one of the components in line causing this.I have seen the cd changer on some models cause this here as well as the radio/head unit as most common on the dash.With all of the electronics in this model here it is difficult to pinpoint the exact source of the draw/drain without the proper testing being done but these are most common for this fault.

The thing is,when you disconnect the fiber optic cables this wakes up the audio components and will cause a drain so this isnt the best check to do here.The best way I have found to locate the source of the draw is following this procedure below.A dealer can actually use their sds machine to locate which component is stuck on causing this as well but the procedure below is usually the best way to manually locate the draw/drain.You will need a multi meter to check this.If you do not have a multi meter to check this then this will need done by someone that does have this tool.

What needs done is to leave the key out of the vehicle with the windows rolled up and make sure everything is off with access to the battery.

Set the meter to amperage or milliamp and disconnect the negative cable from the battery.Put the leads in the multi meter the correct way (negative in negative and positive in the amperage or milliamp slot if equipped).

Connect one cable from the meter to the ground cable that was connected to the battery and the other lead to the ground terminal on the battery,this way the current is flowing through the multi meter.

After around 5 to 10 minutes see what the meter reads for a amperage draw.Normally you want to see less then 50 milliamp or less then .05 amp.

If you see over this amount of a battery draw/drain then your vehicle has an electrical component draining the battery.

From here you would remove one fuse at a time with the meter still in place and observe the reading on the meter until you come across one fuse that allows the draw to read below the 50 milliamp.This is the fuse or circuit that has the component on it that is drawing down the battery.Make sure when you remove one fuse if it is not the issue reinstall it and move to the next waiting a minute between each fuse removed to get an accurate reading.

Once you find the fuse or circuit its on then you would look on a wiring diagram to see what that fuse powers and unplug each of those components one at a time until you locate the component causing the draw then this component would need replaced.If you need help knowing what is on the fuses circuit once the fuse is located let me know.

I dont show the diagram of the fiber optic (MOST) ring on this model here and as above this isnt the best way to check this here.In order for a dealer or shop to see if one of the most ring components are at fault they usually have to disable it with their sds machine and use a fiber optic jumper to loop the ring together.

I would say the biggest one to cause a fault is the Tele-Aid/Mbrace control unit itself as I have had to replace several.

If more help is needed, use the reply tab to continue our conversation. If no further assistance is needed, kindly rate my service.You can rate at any time and we can continue to work on your question as this will not close out your question.Keep in mind in some cases it can be difficult to fully diagnose or help repair your vehicle without seeing it and I work on delivering the best possible answer from what I see to work with.

Thanks Pete

Customer: replied 1 year ago.
Pete, thanks, ***** ***** do the multi meter test and could not see a fuse drawing enough amperage to drain the battery. Anyway the component drawing the battery is not going through a fuse?Why is light not coming through one optical cable but does through another when I shine from the amplifier side to the alpine command unit? Is there a component in between on the optical cable that does not show the light come through?Can you give me audio circuit diagram where it shows each component and its location?
Expert:  Pete replied 1 year ago.

Let me look at some diagrams and I will be right back with you here.

Customer: replied 1 year ago.
Thanks Pete
Customer: replied 1 year ago.
Also is TeleAid-Mbrace housed in the alpine module? if not where is it located?
Expert:  Pete replied 1 year ago.

O.k.,one optical cable connects the amp to the radio then the other at the amp connects to the satellite radio control unit.Then from this control unit to the media interface control unit (if equipped) and then from this control unit to a junction connector then back to the radio.It all works in a loop.Here is the diagram and I apologize as I cannot make it any bigger.

The tele-aid does not look to be on this circuit here.Let me know if you need anything else.Most of the control units are in the rear trunk area under the trunk paneling near the back of the rear seat.

Here is another diagram of what most of the MOST rings look like all depending on what is optioned in the vehicle.

Here is the inline MOST connections the x39/50 location

Thanks Pete

Customer: replied 1 year ago.
Pete, thanks for the information. Images are kind of small but it gives the idea. I will open the door sil and check there. Will let you know if there are any other questions.
Expert:  Pete replied 1 year ago.

Your welcome

Let me know if you need anything else and feel free to rate my help here as this is how I receive credit for my time.

Thanks Pete

Customer: replied 1 year ago.
Pete thanks, ***** ***** quick question. The satellite radio is it housed in the alpine module or is it located outside of it if so then where is it located? Looks like some components are located outside. I followed the optical cable from the amplifier and it goes directly into the back seat . Not in the trunk. So other components which connect to fibre optic system should not be in the trunk. Please let me know it will be a big help.
Expert:  Pete replied 1 year ago.

My info shows the satellite radio control unit ios installed in the trunk on a bracket at the passenger side wheel house area.If your model has satellite radio this is where it is located.

Thanks Pete

Customer: replied 1 year ago.
Pete, thank you very much. I will go take a look at it.
Expert:  Pete replied 1 year ago.

Your welcome