Hello all.
2014 c300 sport 3.5 v6
I've been hunting this battery draw for a bit now. I'm pretty sure I've traced it to fuse 87 in the rear fuse box. The online diagrams I find say it's fire the tele emergency call system. So I've unplugged this fuse to diagnose the draw overnight cuz it's bedtime soon. Anyways when I ran the car with fuse 87 removed I haven't got a check engine light yet and only the sos inoperable on the dash which I acknowledge and it goes away and all looks normal.
I scan with my autel tablet and there are like ten errors ranging from can bus errors to transmission aux oil pump to srs errors.

So I guess my question is are these errors legit and fuse 87 does more than the emergency tele? Or am I missing something? And is the car okay to drive with this fuse out for a bit to be sure it is my battery draw?

Thanks to all who read this and I hope I made sense with my rambling 😀

 

Where the codes there prior to pulling the fuse?

I would put the fuse back in, scan the car and clear all the faults, drive around then rescan the car. See what pops up.

 

Okay so I went out today and installed the fuse 87 and cleared all the codes then restarted the car. No codes except a sunroof code butt the sun roof is damaged and that code had been active a couple off years with no problems. Then I shut the car off pulled fuse 87 and started the car. Now these codes are present with no check engine light and three cast runs perfect.

Hopefully the pictures will help
They should be in order.
First pic no codes fuse in
Second pic fuse pulled
The rest should follow the second pic. Meaning after three second pic the codes pics are in order as they are in pic 2

 

I blew the fuse in my multi meter so tomorrow I will do final testing to see if my battery drain is 100% the fuse 87. Weird if I use my cheap scanner that blue toss to my phone none of these codes are present. Prolly three cheaper scanner cantt see these kinds of faults. I dunno. Had to quit and mow grass so tomorrow is another day 😁

 

When you pull a fuse it kills all modules on that circuit. During the diagnostic test, when those modules cannot be polled, it shows as an active fault. You will need to look at the schematics for your car and find out which modules are attached to that fuse. Then you can unplug one module at a time until you have narrowed the issue down to the faulty module.
I learned this lesson the hard way when I pulled multiple connectors from a can bus junction block, powered up then off and then reconnected them, scanned the car, and ended up with multiple stored faults for can bus failures. Your faults show as current when the fuse is pulled which means the diagnostics test cannot communicate with the modules. Even with the key off, there is voltage on the can bus both high and low and the modules will record any failure of those voltages which can be caused by disconnecting power.
I hope this points you in the correct direction with your diagnostics. Looking up the schematic would do you much good.

 

Very good information. I will find that schematic I might have something like that on my work laptop as I bought a CD with stuff on it off eBay. Thank you yes it helps point me

 

I was searching around online and typed in "Mercedes emergency call system control unit fuse" and came across another forum with someone having a similar issue in an ML. Not sure if I can post links to other forums, but should be easy to find. The thread is titled "W163 parasitic Battery Drain caused by Motorola emergency call module"

I skimmed thru it quickly and he said there are other things on that circuit like SRS, traction control, tailgate switch etc. If im understanding correctly the fix is to repalce the emergency call module, or they say you can use an MD Star Diagnostic and set the module to "not present".

Heres a video he posted:


Maybe this will give you some ideas.

 

Again more awesome information. I am having trouble finding the location of the emergency call module so I can get the correct part number. Seems to be plenty of used ones around. Finding the wiring digram for the fuse was easier than locating the module. Any ideas where to look? I'll be back at it tomorrow if it's not raining.

I just saw that he discusses this at the end of the video. It's first on the list tomorrow.
You guys are awesome and full of resources. Thank you for the guidance it's helping allot. My poor car has had a hard few years and is finally getting some much needed love.

 

Im not sure your sub-model so I looked up a C350 diagram. Shows a Tele Aid/Distress call module in the trunk under the rear deck.

 

I have a 2014 c300 sport 4matic with the n/a m276. I didn't see it there but I suppose it could be on top of the deck area. Kinda where the sub woofer is at possibly.

 

Maybe on the trunk floor right behind the seat?

Heres a W203 thread about the same issue as you: https://mbworld.org/forums/c-class-w...ery-drain.html

 

Should have said in the floor. The module should have an orange sticker on it.

 

So I must apologize that I didn't know this already or have seen it before. I honestly have been in this trunk and had it apart to many times. I never saw the huge plastic cover that is black and up against the rear seats backs. I assumed ort was a black metal cover and the two D rings at the top thru my off. So I decided to knock on it and it's hollow and plastic with all the electronics I have been looking for under it.
Now that I know it's there is so easily identified on the picture of the exploded trunk area that TimC300 posted.

I feel like a dumb kid for not seeing this sooner or was so easy I was looking past it. I always tell myself to keep it simple and I dunno how I got so far off on this one.

Thank you for all the help and patience from everyone. Pics provided to hopefully help someone in the future find this area. I'll be on nights for 4 nights then hopefully my used part will come in and fix my parasite issue for good.

Trunk matt/spare tire cover removed

View from rear seats folded down. Notice the large black plastic cover with two D rings at the top edge off the cover. Remove these two D rings

Well what do you know the cover comes right off.

Satellite reciever for stereo and the tele module under that.

It's facing down in my car so the tell tale orange sticker is also facing down. Undo two screws holding it down. Unplug only the multi wire connector for now and flip the module over to see your part number.

Mine was $35 on eBay

 

Since this had been a learning experience I kinda wanna post all the info I found that helped out. Here is a wiring diagram of fuse 87 and fuse 83 for the emergency call module. This kinda explains why I received all the errors that showed up on my more advanced Autel tablet scanner.

 

Here is a very accurate fuse digrams with past and current fuse layouts that I found handy.

 

How does the car run with the box disconnected?

 

It seems to run add if nothing is wrong. No check engine light no drivability issues. Only way you can tell something is off is the sos unavailable pop up on the dash which you acknowledge and it's gone. That action disabled the economy mode to start stop the engine which I always disabled when I enter the car. I work nights the next few days so won't get much done but guess the battery will not die during then. So a life test while I wait for parts and my days off.

The wiring diagram I posted shows that the modules and fiberoptic that connect to that module are a mixture of inputs and outputs and stereo access to ask questions and dual for help. Each of those modules expect to see something happen and it doesn't happen because I removed fuse 87. So those independent module report errors because they expected communication and it didn't happen. This from what I read can be removed from the system and programmed port of the computers fort a cost at a dealership in sure.