My Comand has no sound, had car scanned, test shows fault Rear signal acquisition and actuation module, Communication on the MOST bus is faulty, MOST bus reports open ring, the software release of control unit "Rear SAM" is not up-to-date.

is this the Harmon amp, i know rear SAM is in the boot but how do i access rear SAM to check fuses.

thanks

 

Rear SAM is the fuse box behind the arm rear armrest. See your owner's manual.

The MOST communications issue cannot come from the rear SAM, the MOST fibre ring does not pass the rear SAM. Of course if the rear SAM does not provide power to some of the MOST devices, you could get that error.

If the car has been diagnosed with a Star tool, it would be good to have the exact fault codes.

 

thanks, i have found how to access rear SAM and Comand fuses are ok, your right indy should have given fault codes, say's his printer wasn't working, do you think it's the amp.

 

You can check f122 (COMAND controller) located behind left trunk panel http://workshop-manuals.com/mercedes...ar/page_14823/ if fine, as DB suggested for definitive diagnose have someone pull fault codes with MB DAS.

 

Thanks konigstiger

one of the fault codes is D104 MOST component at position 4 reports open ring.

 

I have the same problem Same error code. Did you fix the issue?

 

Components (radio, amp, etc.) are arranged within a closed MOST (fiber optic) loop. D104 = position (device) 4 so you need to identify this unit. Xentry (MB diagnostics) will should give device. DIY, you will need a fiber optic bridge (bypass) to remove each device one at a time from loop to confirm which is malfunctioning.

 

Thanks Konigstiger, I imagine the Amp is the last thing to check as it applies to the sound once I have checked all the components (VC, Bluetooth module, sat Module and ofcourse the HU)

 

I'd caution against updating the rear SAM... it brings in bugs as they flash with facelift software that they shouldn't. My diagnostics also complains its not suitable (autel) if it wasn't for the bugs I'd say autel are wrong but sadly it seems a third party understands the car better than the manufacturer

if you have an issue with no station names or frequency displaying on the radio when you lose sound, its always a dead amp (its a more reliable failure than expecting the sun to come up tomorrow)

 

Thanks Botus. Yes indeed, I used an Autel scanner which gave me the D104 position 4 code. And when I lose sound the radio station identifier / frequency and name do disappear. I have ordered the MOST jumper and will check the other components, which seem to work when I do have sound. I guess my next option is to get it checked by a Star scanner before I start changing or getting pars repaired.

Thanks for the pointers.

 

100% dead amp, happens on every single 221... bloke on this forum in USA claims to repair… which would be nice as no one seems able to do this in Europe with a long term fix

 

I did contact Alexander and will be shipping the amp to him. I sent him a video of what was occurring with the car audio.

Thanks Botus, I really appreciate the communication.

 

I know its really difficult to find blokes in the UK. I have lived in the UK for many many years and always had to hunt for guys to work on the mercs I owned while there. I did find a bloke who lives out in Windsor who does these kind of repairs. I wonder if he is still around

Cheers Mate.

 

So a 3 day job. Why would a SAM fail? All I did was blow high pressure aid around it.

 

I’m currently having a similar problem with my s550, I have no sound, or no station list. I recently took it to the dealership, the diagnosed it with error code D104, the told me it was most likely the satellite radio module. I replaced the Sirius satellite radio module, and nothing. I’m thinking about ordering a new amp but I’m also curious as to what other possibilities it could be?

 

the dealer needs shooting - with the trim out the way - it takes seconds to loop out a Sirius module to test their wrong theory

dead modules give issues - but a dead amp give no sound and no station display on FM - a dead amp is as likely as a empty fuel tank - a dead lingatromic or sirius module is as likely as your 7th puncture

 

so, my best bet would be to order a new amp?

 

diagnosis is cheaper... or borrow another amp first and test theory

 

Position 4 is the TV tuner. get one of these and trouble shoot each component.
https://www.ebay.com/itm/223136521415