c300nubee

Hi,

I was replacing the battery in the trunk of my 2013 C300 Sport and, like an idiot, performed the procedure with the main battery still connected.

Anyway, the ground wire from the rear battery slipped my hand as I was trying to install it and shorted on one of the connectors near that small battery, so now my car is acting really weird. I am sure I blew out something, now the trouble is going to be trying to find what is busted... :-(

I have tested all the fuses in the engine compartment (near driver) and also those in the trunk (passenger side) and all the fuses are good.

The car does turn on, but it displays some new messages on the status display in the dashboard:

1. SOS mbrace inoperative
2. Check rear left side marker lamp
3. Check rear right side marker lamp

The figure of the engine (check engine light?) is also now lit up next to the low tire pressure light, the ECO light near the A/C is OFF and you can't turn it on clicking the button, the trunk won't open using the remote (nor using the button on the driver door), the panic button on the key does nothing now, and when I lock/unlock the car, the passenger side light on the mirror does not blink and neither does the rear right light.

I did test the turn signals and they all (front and rear) are fine, but the what's interesting is that it seems to me that the right rear turn signal is the one that should be blinking when I lock/unlock the car but it doesn't do it during lock/unlock.

I am going to connect an OBD II reader tonight and see if I get a code for the check engine light.

If anyone has any pointers, I'd appreciate the help!

Adi-Benz

A regular obd2 probably won't help you will probably need one for Mercedes like iCarsoft to get more elaborate codes

c300nubee

Fixed!

Basically, I ended up burning a 200 AMP (yes, 200 AMP) fuse in the pre-fuse box. This pre-fuse box has several high amperage fuses in it but is "supposed" to be non-serviceable. In other words, Benz does not want you opening it and replacing fuses within it. They actually built it in a way that is not simple to open up, but no impossible. Why did they do that? I don't know and quite frankly don't care. Anyway, a replacement pre-fuse box costs anywhere between $250 and $300. There are also one or two relays inside the pre-fuse box, so it is not just fuses. You can test the fuses without having to open the box, but you do have to remove it from the car to test its fuses comfortably.

So, after I removed it, I figured I was gonna have to buy a new one... So I said well, let's open this up first and see why they'd make this unserviceable... So I opened it carefully (it took me about 1 hour total to figure out the trick and to actually do it) and found the culprit fuse, which I could easily remove and so I replaced it with an identical $7 fuse from Amazon. So, I put the part back on the car and voila! All issues solved.

Hopefully this help someone some day.

gamma300C

Well done. Would you mind sharing exactly where that the "prefuse" box is on your C300/ A picture would be great if possible. Got a link to that Amazon fuse purchase description too? Looks like these?

Much Appreciated,

c300nubee

The unit is right next to the main battery, basically it is the part that has the big red plastic square lid covering the positive jumper cable hook-up terminal. The link to the fuses is:
In case that amazon link stops working in future, the fuses are made by Blue Sea Systems and are called AMI/ MIDI Fuses

gamma300C

Thanks...stored away your post for future reference.

Sig Dani

a example of how the pre-fuse box looks inside and what you have to disconnect to have acces to it

meazz1

Glad you fixed.
How did you know this was the issue?

Moto_Guzzi

The most worthwile info I stumbled apon in a long time, slight problems here can cause a lot of mahem, difficult to find.

Glad to see its properly protected.