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Ask Michael Warfield Your Own Question
Michael Warfield
Michael Warfield, Factory Mercedes-Benz Technician
Category: Mercedes
Satisfied Customers: 3142
Experience:  Mercedes-Benz Master Certified technician
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I just installed a replacement MCS unit in my 2003 ML-350.

Customer Question

I just installed a replacement MCS unit in my 2003 ML-350. My ML has the fiber optic ring. The replacement unit came with the green blank covering the fiber optic module so I have to assume it is not activated. I assume this because I don't have sound and it is not recognizing the 6 disk CD player in the back. Do I need to have the dealer version code this radio to work with the fiber optics?
Submitted: 1 year ago.
Category: Mercedes
Expert:  Michael Warfield replied 1 year ago.

No, the green blank on the back of the MCS should pull out and then you can insert your black fiber optic connector.

Expert:  Michael Warfield replied 1 year ago.

There is no activation needed for the MCS. When you turn it on, it should light up at least one side. If its not sending the wakeup signal, it is probably a defective unit. The MCS will send a wakeup as soon as the power is turned on.

Customer: replied 1 year ago.
I did that; however there is no signal coming from that port. Everything else on the system appears to be working just fine.
The nav, fam, am but no sound and no recognition of the 6 disk cd player. I have read that these radios often need version coding using the star system. Is that true?
Expert:  Michael Warfield replied 1 year ago.

You only have to version code the radio to get rid of some fault codes concerning the actual and specified configuration of the D2B ring. I have replaced many of MCS units and they always worked when plugged in, I proceeded to version code them after it was working. Are you sure there is not another component taking down the D2B ring? If one component is malfunctioning, the whole entire system is down.

Expert:  Michael Warfield replied 1 year ago.

I usually have problems with the tele-aid module underneath the back of the passenger seat. I disconnect the fiber optic connector and install a looper/jump connector.

Customer: replied 1 year ago.
I understand that it is a ring but everything was working fine minus FM prior to this replacement. It seems the FM amp in the original radio died as AM, WB and CD all worked. I can check the new radio again but it appears that the Fiber Module in this one is bad if it doesn't require activation or version coding. The big difference is this system has the NAV and the one I had previously did not.
Customer: replied 1 year ago.
Tele-aid seems to be working fine but I can loop it just to be sure. Right now I am sitting with 2 systems and neither of them are fully operational.
Expert:  Michael Warfield replied 1 year ago.

Did you buy the MCS used?

Expert:  Michael Warfield replied 1 year ago.

I agree with you that everything else should be fine since just the FM was out. That is a common problem with the MCS. I suggest you try exchanging the unit for another one.

Customer: replied 1 year ago.
I bought the MCS used. I just put the old back in and I get sound from the CD Player but when I put the used one in I get nothing. I also noticed that the fiber is blinking in the back of that radio. Just no sound. Not even static. This is the 3rd replacement. The 2nd on gave me CD player sound only but no FM. AM or WB. I can't figure this thing out for the life of me.
Customer: replied 1 year ago.
With this one in there I wasn't even able to open the CD player in the back. It is sending light signals but apparently the amp and the CD player are not receiving them. I work with fiber optics so I will clean the contacts once and see if that makes a difference.
Expert:  Michael Warfield replied 1 year ago.

cd player should eject even with no light signal. It's controlled directly by the eject button so that seems unusual. I think you have an intermittent problem. Does the eject button light illuminate on the cd player? It should if it has a good power and ground.

Customer: replied 1 year ago.
When I switch Head units I can hear it power up and can eject the cds. I think the issue is that this is a fiber ring as you said. The replacement unit is sending signal through the fiber optic ring because I can see that working. What I have been able to find out and am not sure if it is correct or not is that the replacement radio came out of a Mercedes that didn't use the FO ring. Because of this there are disabled functions on the radio and it doesn't communicate with the tele-aid module or the amp causing them not to forward down the ring. I am going to keep doing research and see what I can find out.