Titus

2016 C300 4Matic
I went outside a few days ago and the trunk was open. I think I had accidentally hit the trunk open button on my keys.
Apparently, the battery got drained. I went to start it about two days later and the battery was was completely dead. I attached it to a trickle charger an let it charge for a few hours.
Everything turned on, however the engine would not crank when I attempted to start it. I took it to the local auto parts, they put it on their charger and made sure it was fully charged and tested it, which it passed.
I reinstalled the battery, same problem, electronics turn on but the engine wont crank.
I am getting a traction control inoperative warning, power steering malfunction, and service required warning. why would these be turning on from a dead battery?

Today I pulled the starter fuse and starter relay. Tested both and they are both fine.
So I'm not sure what to look for next. any ideas?

W205C43PFL

I would also check the aux battery as it is possible that, because of the starter battery got discharged, it strained the aux battery.

Titus

Thanks for the tip. I replaced the AUX battery, still no crank no start...

I remembered I had an OBD reader that connects to my phone via Bluetooth. Here is what it says:

W205C43PFL

Hmmm, I wonder if for any reason it thinks something happened (ie. collision) and disabled start, if so need to renable start through Xentry or a very specific third party scanner that deals with Mercedes. I forgot which one has it but I remember seeing it. Xentry is not a must if the scanner has the feature/function. What you could try is erasing those pending codes and see if it does anything in the meantime.

Titus

So quick update. Had to take it to the dealership. They found some kind of wiring issue to the electronic steering. I'm trying to get more details right now, but the ESL wasn't able to communicate with other modules.

Now they're telling me that my brand new battery is no good, and they want to charge me $650 to replace the battery and "calibrate" it. Has anyone heard of this before? Sounds like dealership scamming to me.

Cosworth2000

Here is the problem. When your battery died the modules all reset however when you charge the battery, the modules didn't like the battery for some reason as they need full power after module reset. How old is the battery? I have noted that AGM look like they have a full charge after discharge but that does not seem to be the real case to the car. I would go an purchase a new AGM and install it and your problems should resolve.

Titus

So I got a final resolution on this. Turns out the neighborhood rabbits chewed on a wiring harness connected to the power steering under the car. The battery drainage was possibly a symptom of this. Once the wiring was repaired & rewrapped, the car started up with no problems and no codes.
They also told me that the battery needed replacement, as I put in the other thread. I politely declined, and sure enough, when I got the the dealership, the car started up just fine and the battery was just fine.

Cosworth2000

Wow.. now that is something only a dealer could find.