Hey Fam,

I have a 2009 C300 that is giving me all sorts of electrical trouble.

Day 1:
All of this happened about 5-10 minutes after I left the car wash. I first noticed my a/c stopped blowing cold and my check engine light came on. As I continued driving I noticed my turn signals weren't working either. Further down the road the brake light and the high beam light illuminated on the cluster and went on and off for a little bit and now is always on. At this point, the Airbag light came on for the passenger and I immediately parked the car after getting home. After parking, I realized my headlights and taillights were turned on and didn't turn off at all after several minutes. So I removed the positive battery terminal to keep the battery from draining.

Day 2:
I attempted to drive the car but it didn't crank over at all. The same lights were on the dashboard but this time there was an "inoperable" warning with a picture of a car and skid marks behind it.

Day 3:
I tried starting it and it started right up with all the warning lights still on.

Day 4:
In the morning I tried to start the car but no luck.
Same day in the afternoon I tried to start the car and it started right up so I loaded it onto my trailer and going to take it to the shop
After loading it I plugged my scanner into it to read the codes but it couldn't communicate with the car at all, and have used the same scanner before without any issues.
After loading it on the trailer I attempted to start the car and turn it off several times and it failed to start once and started up 3 more times until I decided to stop messing with it.


Does anyone have any clue what is going on? I'm thinking one of the fuse boxes (sam modules) got water inside after the carwash because none of these issues ever happened before. If this is the case, how do I test the sam modules?
******PLEASE HELP******


I will post issues down below:

-turn signals not working
-red brake light on the dash is illuminated
-high beam light on the dash is illuminated
-check engine light on - I plugged in my $6000 scanner and it couldn't communicate with vehicle, although i've used this same scanner and worked fine
-a/c not blowing cold anymore
-when you park the car and lock it the lights don't turn off - I have the switch set to "0"
-passenger airbag not functioning error on dashboard

 

how long did you leave the battery disconnected? if you let the car drain the residual power that is left then there is like a soft reset for the computers. over night works... where would water get in to damage the sam (rear or front)? is there a hole somewhere or did you leave the front sam box open? the physical module that controls the headlights is faulty, like many things in the car. in the off position mine illuminates the right side of the vehicle and has drained my battery and caused premature alternator failure on my 2009 c300 4matic. visually inspect sam(s) and while you are there look for corresponding fuses for the parts that are failing. I'm not a mechanic but I've been through it with my car and have only learned by working with it hands on....

 

The battery was disconnected for about 18 hours. My suspicion is the front sam module because all the problems I am having are controlled by the front sam. I have two theories as to what happened.
1. there is a small part of the rear taillight that is cracked and broken off a small chunk, and it is about the size of my pinky. I think water might've gotten in through the taillight and shorted out the front sam since the front sam is what controls the lights.
2. when I first opened up the hood after the car wash I noticed that the sam module cover wasn't fully seated covering the module. It was maybe 1/2" to 1" off towards the front. So whoever opened the module before me didn't seat it properly and water might've gotten in through there.


However, I didn't notice any water residue on either the front or rear sam modules. Not sure how much water needs to get in before it does damage.
I've also checked all the fuses and they were all good besides my cigarette lighter.
Today when I took the car from the shop I brought it to, they were convinced that the ecm was bad. I didn't agree with them because the car occasionally starts which if the ecm is bad the car won't ever start.. mine does... sometimes lol. So there is no way my ecm is fried. Plus it doesn't explain why my lights are acting up. The ecm doesn't control any lighting module, they are all controlled by the front sam unit. He blamed the "bad ecm" for the lights acting up which tells me he doesn't know crap about MB. The sam units are the gateway for power. Everything runs through them before leading to the actual part. So if the front sam is bad it would explain why the ecm heats up when the car isn't running and the reason why there is no communication with any of the communication systems when I plug in an advanced OBD II scanner.

I'm planning to remove the front sam and open it up to see if there is any visible damage like a blown fuse/breaker.

 

Take photos, like to see.

 

That front SAM is right next to the water drain which if blocked will send water right onto her. The rubber gasket at the base of the driver's side wiper arm if torn will also send water down to the rear of the SAM. Certainly suspicious re; your car wash story. Loosen up that module to access underneath, if you have compressed air, blow her out, contact cleaner, and fuse check as you planned might help.

 

Update:

I checked under the hood after it had rained a few hours ago and saw water accumulation right on top of the cover of the sam module. After seeing this I decided to rip apart the sam module to get a better look and found 2 different plugs/sockets that had a decent amount of corrosion. At this point I know 100% the sam had contact with water and is possibly fried. I cleaned everything up and checked to see how things were. Car started up fine and none of the issues mentioned above were present for about 3 seconds, car was running strong. Then all the warning lights and issues came right back and I could feel the car running like ****, every time I put it in gear it would be extremely rough and rock the whole car and eventually stall out. Also,all the lights on the car start to flicker. I found that when I keep the battery unplugged for a while I can get the car to start.. sometimes lol. I ordered a used front and rear sam module today and going to try swapping out the modules to see if I can get the car running right again.

I still couldn't communicate with the car when I plugged my scanner into it. So I tore apart the front right fusebox that has the positive jump start terminal on it. I found that all the fuses were good except there was no continuity for one main fuse/part. I don't even know what this part is called but it's attached to the fuse box and my Mercedes mechanic friend told me it is like a fuse and blows when you get in an accident. So what I did was I bridged the to connection points and removed that fuse/part-thing and bypassed it and Vola! When I plug my scanner in now I can get the codes off of it.

Current codes:
C164- no CAN message was received from control unit N22/1 (AAC [KLA] control unit)
C141-no CAN message was received from control unit N93 (Central Gateway control unit)
C121-no CAN message was received from control unit N47-5 (ESP control unit)
C103-no CAN message was received from control unit A80 (Intelligent servo module for DIRECT SELECT)
C126-no CAN message was received from control unit N80 (Steering column module)

Lastly, my mercedes friend told me to check under the front carpet, which when I did I found the foam to be wet and a little bit of water, nothing crazy. I've seen on other threads where people have puddles of water which wasn't my case but my friend told me that even a little bit of water/moister can corrode the cables underneath. The cables under the drivers side carpet is all CAN wires. After seeing this I took apart the connections to see if there was any corrosion but I didn't see any. So after thinking about it I still think its the sam module(s) because it had decent amount of corrosion and it is the only thing that controls all of the issues I'm having (except the engine running like **** and stalling out..idk about this). Any advise or thoughts are highly appreciated, thanks fam

 

Since new , my dealer was ordered never to wash the engine bay or the interiror of the car, no fiddeling with knobs etc by unsensitive hands and fingers, no washing. So only the shell of my car was ever washed by only me.
If washing is left to others you just never know what is going to happen, and how it will effect your pocket. That was advice I got before buying the car.

 

I've never washed the engine bay either, it was always an exterior wash.

 

I have the exact same situation that you had in my vehicle. Everything you mentioned I’m going through, did you find the error?
or did you sell it and somehow ended right into my hands? 😂 I gotta note that my car was fine and also started after I got a car wash and let it sit overnight, then tried to use it in the morning and it was all bad

 

My 2009 c300 just started suddenly today all the same wonky things going wrong. No car wash tho and no recent rain.

 

Check you bosch voltage regulator under the alternator

 

Last update:
It ended up being the front Sam module (fuse box). Had lots of corrosion on it and was basically fried. This is basically the gateway for power for almost all electrical components in the car. So I first pulled mine out and got the part number and went on car-part.com and called local junk yards near me that had one with matching or superseding part number. I paid about $150 for a used Sam module and put it on and everything was back to normal. All problems solved. I did have my friend hook up his mb scanner and adjust headlight auto turn on sensitivity and that was pretty much it. Hope this helps everyone else.

 

i'm having the same electrical issues with my 2010 Mercedes Benz c300. It starts and runs but the dash is flickering, the key fob doesnt unlock or lock the doors, windows wont roll down, radio, air/heat doesn't turn on, the turn signal lights dont turn. The head and taillights stay on with battery connected and they dont turn off when battery is conncected and the brake lights work fine. I took it to a mercedes dealer here but they stated that I needed a new front SAM which was ordered and programed. After programming the SAM they stated that it could be water damaged under the carpet and that if that is the case they couldn't do anything about it. Which I believe they didnt want to deal with it and they were so far backed up that they didnt want to keep dealing with it. I got the vehicle back home and recharged the battery up which once i connected it back to the car thats when it started and was running actually good but has those electrical issues. Any Suggestions or feedback?

 

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im having the same issues with me 2009 c300 so far the solutions I have come across are, replacing front Sam box (make sure numbers match so you don’t have to reprogram computer) and replace front distribution block under driver seat (make sure numbers match so you don’t have to reprogram computer) then reset transmission (easy YouTube method) then seal front windshield wipers and clean sun roof holes.

I have already replaced my fuse box and my distribution block comes in 2 days hopefully that will get my car back running... will update in 2 days and I will leave my car unplugged so it helps with the soft reset I read earlier

 

Glory to God, so so happy my problem has been fixed, it worked plz if you have this problem tell your mechanic to change the Sam box and the distribution block first 😁

 

2012 c300, I’m having all the same issues and I’ve changed the f32 pre fuse box alternator and battery and still in the same position. Can you please share the part numbers and location of the distro ?

 

[QUOTE=madmario60;8561766]im having the same issues with me 2009 c300 so far the solutions I have come across are, replacing front Sam box (make sure numbers match so you don’t have to reprogram computer) and replace front distribution block under driver seat (make sure numbers match so you don’t have to reprogram computer) then reset transmission (easy YouTube method) then seal front windshield wipers and clean sun roof holes.

I have already replaced my fuse box and my distribution block comes in

 

Problem solved. I was experiencing the same issue as you, and after reading all the comments, I realized that the mechanic who advised you to check for water underneath the driver's side was correct. I inspected my car and found it completely filled with water. Initially, I thought the water was in the door, but when I lifted the carpet, I discovered it was beneath the driver's feet. I uncovered it, let it dry, and ultimately, that resolved my problem.

 

I removed the plastic drain hole plugs so water wouldn't collect again if it rained hard enough to cause water to infiltrate the car. Underneath there is a plastic splash-shield that should keep water from entering, but the hole keeps the water from pooling and filling the floorboard.

 

Here's an issue I had caused by the water: P0178 Solved