Want to share my story with the forum to see if anyone else has experienced what is going on with my 2011 E550 coupe. After a major rainstorm approx 1 year ago, my radio unit stopped working. The command screen would boot up when starting the car, Mercedes logo briefly appears on the screen before shutting down and restarting only to shut down again. This cycle would repeat itself until I would actually power off the system manually. Checked all radio related fuses, replaced #26 but still nothing. My initial thought was that the fuse located behind the radio unit may have blown after the rain storm.

About 6 months later, the system randomly powered up while driving, along with command screen display for radio, nav, phone, etc. All worked as normal, with the exception of the radio randomly shutting down and restarting while driving. Ultimately, the radio would play but the command screen would not boot-up. In those instances, I would manually reset the radio by holding the power in for 10 seconds at which time the command screen would come on as normal. The radio unit, that would not power up for 6 months, would now come on each time when starting the car though.

Suddenly, my battery was mysteriously draining leaving me stranded multiple times. I also notice that the radio could also be turned on manually even with the car off. I suspected this was the source of the drain. For some reason the radio is not powering down when the car is turned off.

I had my 18 month old Interstate battery charged and checked, which came back a a good battery. Upon reinstalling, I pulled fuse #26 to test my theory and over the course of 2 weeks with the radio unit inoperable from the fuse removal, I have had no issues with starting the car, quick, effortless starts each time.

Curious if anyone else has experienced this issue and what did you do to resolve the issue?

Thank you in advance for your feedback!

 

Sorry to hear of your troubles. That is an interesting issue indeed. Did you see or smell any evidence of water intrusion besides the proximity of time between rain storm and the initial issues? Have you been monitoring your voltage and amps through the instrument cluster during different conditions?

A forum member had mentioned chasing battery drain on his W212 and concluded that if you plugged a device or ipod into one of the factory glove box adapters and the device powered on without the ignition being on, that it was a sign of the COMAND unit draining power. I wish I remembered the thread (or title) as it was a long one, but I do remember it was made by S-Prihadi who is an extremely knowledgeable member.

I've had (and have) strange subtle electrical and drain issues on my 2010 E350 207. I do actually use my old school 2014ish ipod classic w/ the factory adapter, and it does power on with the car completely off. I have smelled water after heavy rains, but yet to find any evidence of intrusion.

Sunroof drains seem 100% inaccessible in our cars, a huge rabbit hole I got lost in. I suspect my passenger side, as it drains slower and less water than driver side. External drain holes are somewhere near the center of the car underneath the side plastic paneling which conceals the brake lines and also just before the front tires in the wheel well, buried in the chassis and 100% inaccessible. No rubber tube like on 204's. Still need to inspect that. Also the grommets around the wiper blade arms.

I did go around and clean all of the ground locations I know of (11 I believe?) besides the one under the front drivers carpet. My battery stays charged almost permanently now and continuously has the alternator pumping 14.1 - 14.8 volts during driving. Neither were the case before cleaning grounds. Things still aren't right though, and I also have slow(ish) cold starts. Slower and weaker than they should be, and warm starts are stronger. Sometimes voltages drops to 11v on startup, lowest I saw was 10.6. If I see that, it gets the Ctek charger thrown on it overnight.

These are strange issues that I've barely made headway on myself, but curious to your situation and hope I could at least give you a few things to think about. I wouldn't hesitate to remove the COMAND head unit and glance at the wiring in the back for corrosion, etc as well as getting a proper scan tool on there and seeing what codes, etc have to say.

 

Thanks for your reply and for sharing your experience. I have concluded that the radio head unit is bad from the water damage. Since removing the fuse, I have had not had any issues with the battery draining. I found a similar unit online for $200 and planned to have it installed by a local installation shop. I will check back once it is in and working to update on the battery drain situation. All good for now, just no radio, nav, etc. without fuse #26. .