Hey guys! I'm hoping for some help here... Long story short my radio (Audio 20) cycles on and off continuously, and recently lost my eco stop-start function. I have replaced both batteries, checked all fuses, checked CAN wave forms (all seem well and within parameters), ran diagnostics countless times and cleared. The codes that consistently reappear and show as current are:
B15D814 THE CABLE FOR AUDIO MUTING IS FAULTY. THERE IS A SHORT CIRCUIT TO GROUND OR AN OPEN CIRCUIT
U113E00: COMMUNICATION WITH THE BATTERY SENSOR IS FAULTY
B214B15: THE OUTPUT FOR THE NO-LOAD CURRENT ON SWITCH IS FAULTY. A SHORT CIRCUIT TO BATTERY (+) OR AN OPEN CIRCUIT EXISTS

I took the car to my local Mercedes Dealership... They charged me roughly $500 and told me I needed to replace my battery temp sensor. I did and it did not fix the problem. Actually, the readings from the new sensor are the exact same as the old one:
Charging current or discharge current at battery 14.77722
Battery Voltage 65.54 V
Battery Temperature 419.9 F
Strike 1...

Then they told me I needed a new head unit. I bought one and it does the exact same cycling on and off that my original one does.
Strike 2...

Desperately trying to avoid a costly strike 3, I collected my car and decided to work through this myself. Strangely enough, I measured the voltage at the battery temp sensor connector blue/white wire (not the actual battery sensor) unplugged and got 10.2V, then left it unplugged and got 9.7V at the Rear Sam connector blue/white wire. That wire, according to AllData, should run straight from the battery sensor to the rear SAM. Can anyone out there help me figure out what kind of electrical tomfoolery is happening here and how to get my radio (most important) and eco stop-start back?? Any help would be greatly appreciated!!!

 

Slight chance your battery needs replacing...

Otherwise looks like a wiring or SAM issue.

 

I know it’s an old thread but hoping OP got it resolved and is still around to tell us the story. I’m in the same boat 😭

 

OP here. Sorry you’re experiencing this issue. It’s really frustrating. Although some have been able to fix the problem with a head unit software update, I wasn’t. I was ultimately able to fix the problem by buying and installing a used head unit. Turns out the one I had was not the correct model number for my car. Seems the previous owner installed it and it worked for a while but ultimately failed during my ownership. As an aside, beware if you do, You will have to replace the new head unit’s vin to match your car’s vin using Star, and the dealerships will not do this for you. It is not plug and play. Good luck!

 

Thank you for the response! It’s the only thing I haven’t tried yet. How’d you know the one you had wasn’t the correct model? Called dealer parts?

 

I removed the headunit and took a picture of the model number on the sticker on the unit. I then went to a Mercedes online parts website and checked the listed compatible model numbers that matched my vin. Turned out the model installed in my vehicle was not listed as compatible to my car, so I ended up going on ebay and finding one that was. I programmed in the vin to the ebay replacement with the pin and got it installed and working properly. It's not terribly difficult if you have Star. I'm sure the process is described in one of my posts on mhh auto regarding my issues with the head unit. Good luck!

 

RESOLVED: I have no idea why because I definitely don't recall messing with it but maybe I was distracted one day and moved around the fuses or someone played a dirty joke on me.... There was a fuse missing in fuse box: K40/5 slot F475 (it was a 40 amp fuse).

I've attached a picture and circled the fuse that WAS missing.