W212er

Hello, I recently purchased a water-damaged 2014 W212 Facelift and it has a few issues I’ve been chasing. I'd be grateful if anyone could help. I’m familiar with electronics but still need to figure out what to focus on.

Issue #1 Tailights:
The tail lights don’t light up when the headlights are on but they still seem to have some functionality. The outer lights come on when I brake, when I go into reverse the inner white tail lights come on, and when I signal, the outer tail light blinks but clicks faster. I pulled the driver and passenger carpet and started messing with the brown CAN and noticed that when I unplugged one of the wires on the passenger side the tail lights would come on. This CAN stem seemed to communicate with the right doors, sunroof control, and possibly the head unit. There was one more on the passenger side and one on the driver's side would also cause the tail lights to start working. My scan tool says that the rear SAM is throwing codes for the lamps saying that they either have a short to positive or are an open circuit.

Issue #2 The Headunit:
The Mercedes logo comes up for a few seconds then the screen goes black, the backlight is still on but it doesn’t show anything. During those few seconds if I go into reverse the backup camera works but soon after that goes black as well. The radio plays and the volume up/down knob seems to work but nothing else works, I can not mute, change the channel, take in/out CDs, etc. When I go to the audio tab on the instrument cluster it just shows “_____”. I tried to read the codes with two different scan tools but they froze and made them unresponsive. Using a different tool I was able to confirm that the VIN in the head unit matched that of the car and the only error I got was about some mute cable shorting or being an open circuit. I’m not afraid to take apart the head unit but I’m not sure if the issue actually lies with the head unit or something else.

Issue #3 Driver Side AC:
When I turn on the AC cold air only seems to blow on the passenger side, both driver-side vents blow warm air no matter what I have set. My scan tool reports that the left blend flap is not working correctly. Also likely a coincidence but the blue arrow on the AC controls for the driver's side doesn’t light up. The passenger side seems to be fully functional.

Here is what I’ve done so far:

• I’ve cleaned all the CAN connectors and grounds in both the driver and passenger side footwells.
  
• The ground connectors near the Rear SAM were also cleaned as well as all the fuses and relays using a wire brush and contact cleaner.
  
• I also replaced the passenger side brown CAN distributor since it seemed pretty corroded on the inside.
  
• I measured the resistance of the distributors with a DMM and all the resistors are consistent with each other.
  
• The Main and Aux batteries have been replaced with new ones.
  
• I cut open the left taillight and touched up everything I could with some solder but that didn’t change anything.
  

Any help will be appreciated

Thank you

Rickman30

There are videos that show how to repair the broken solder joints in the tail light housings for the LEDs. Seems a somewhat common issue.

The COMAND screen sounds like is dying, or the power supply chipset in the screen module is shorting. There are a few Mercedes module repair shops online. I used the one in Miami FL to repair my COMAND when the speaker outputs shorted. MandBspecialists. They were quick with repair and return shipping, been over a years since the repair. But do your due diligence and search and evaluate before pulling the trigger.

There are electronic motors that operate the doors in the HVAC system. You will need Xentry for instructions on testing and repair.

Rather than disturbing ground points unless you can see evidence of corrosion. Do a voltage drop test to confirm continuity. Use a Multimeter, preferably DVM,Digital Volt Meter. Connect the negative lead to negative battery terminal, with engine running and headlights on high beam, a/c fan on high, radio on, to load the systems, touch red or positive lead to the eyelet of the ground wire you are concerned about. And don't touch the stud or the nut holding wires eyelets, you're looking to see if the connection between the stud/nut and eyelets is good or not. Your reading should be 0.056 or less, if over, the ground is compromised and needs attention. To test engine ground, touch red or positive lead to engine block while running, results should be as mentioned previously. If you are unsure of my instructions, search videos for "Voltage Drop Testing"

When cleaning corroded grounds, you will end up with dissimilar metals, meaning they will corrode faster, protection will be required. I recommend dielectric grease applied to eyelets before installation. The grease is non-conductive, but when tightened to the stud, it creates a sealed from weather connection. You can use the voltage drop test to ensure your connections are sound. If not loosen nut and re-torque, then re-test.

Good luck.

CaliBenzDriver

I'll look deeper into this to help Rick.

What scanner are you using to see your fault collection.

Get your chassis diagram to work by bus type around issues you're having.

W212er

Thanks for the replies. I currently have access to WIS and Xentry. In Xentry when I opened the CAN diagram the only module on the Brown CAN that had a warning was the Rear SAM. All the warnings were about the lamps and signal markers being either shorted to positive or an open circuit.

CaliBenzDriver

That's pretty good news unless you have missing unreported modules.

Both SAM are the power management backbone. They must be A-ok or hell is going to be all over the chassis from poor relays, fuses, CAN-B/C,.... We don't exactly care about missing light signals so much than bad SAM are significant.

Are your water damage limited like regular leaky roof or extensive like a local flood ??

How would you say is your voltage control and battery life??

What's your priority target?

W212er

Thanks for your quick response.

Both batteries are brand new and while the engine is running the voltage is around 13.9V - 14.1V, and with the engine off and a brand-new battery it was around 12.3V. I remember when I had just replaced the battery and ran Xentry without the engine on it complained that the minimum battery voltage should be 12.5V to get proper readings. If I remember correctly, Xentry showed me 17 modules on the brown CAN.

I'm not sure how exactly the water got in, but the damage seems to be mostly electrical and was more prominent on the passenger side. In the passenger footwell the GND near the seat was corroded and near the Rear SAM there was some light corrosion. I opened up part of the SAM expecting to find a bunch of corrosion, but it was nearly spotless on the side I could see, the PCB was secured with melted plastic standoffs which I'd need to break to actually take the board out, so I stopped there.

First, I'd like to get the taillights working since I can't drive at night, then the Head unit, then the AC. I've also noticed that the lumbar control doesn't work on both front seats, the rear sunshade doesn't go up, the trunk opens really quickly, and the auto-close buttons don't work. It's my understanding that the trunk should open gracefully but this seems to swing open full speed, is that how it's supposed to be? When I measured the wire going to the buttons for closing the trunk I noticed that there was 12V going there and the Ground seemed good, but I'm not sure if any of this is related to the other problems. Also, I couldn't find any pinched or cut wires going up to the trunk lid. Something I'm still confused about is why the taillights begin working once I disconnect a specific CAN wire from the distributor in either the driver or passenger footwell. I took out all the fuses and relays from the Rear SAM and made sure they worked. Are there any other connections for either the Ground or the CAN that could be problematic?

Bruce Hubbard

Poke a wire into the plug at various points that goes into the tail lights and check for voltages
There's some additional info on the resistors now just added here:
https://mbworld.org/forums/e-class-w...ml#post8987833
For the Comand display, swap it out. You can get them on AliExpress
I swapped mine out a while back and now it looks like new

W212er

The previous display had a bunch of dead pixels, so I replaced the display, and the new one seems to work as it shows the Mercedes logo and backup camera briefly because of this I'm more inclined to think the headunit isn't functioning correctly.

Bruce Hubbard

Looks like it
One from the wrecking yard and swap it out
See if they will give a restock if it doesn't fix it

CaliBenzDriver

Here's what I got:
right inside had consequent water damage (not flood!)
Based on testing CAN-B Accessories are down
Unplugging bus bar lets R-SAM work!

To capitalize on this information, I can give you a 5mn task:
unplug RF SEAT MODULE from under it or from busbar.
Wich ever you see your research well spent.

When CAN-B is disrupted you get impacted usage. The best part was you testing to identify a particular connector... what module name seat by any chance or door... scan that bus.

What would you do Rick ??
I used to be fan of Mitchell's printed diagrams stacks well organized.

W212er

I had previously unplugged the Right Front door module from inside the door, but it didn't seem to make a difference. The CAN connector that I unplug which fixes the taillights is somehow related to the Right Front and Rear door, Sunroof controls and Radio because they stop working after I unplug it but I'm not sure if the door module itself is actually the problem.

Sorry I misread what you said. I have also totally unplugged the front right seat but that didn't seem to change anything. Also is it normal for the head rest to move up and down when you move the right seat forward and backward, because mine does this.

Bruce Hubbard

So when motor not running and you select parking lights (anticlockwise one step from auto position, on lights switch), and driver door is open
tail lights not working? any tail lights at all ie trunk or body ? any ding ding sound ?

W212er

I'm current not home but when the door is open and the key is out the cabin lights all work. The parking lights did work but I can't remember if the tail lights worked when all tbe CAN connectors were plugged in. Also when the door is open the courtesy lights work.

W212er

I also forgot to mention this previously, but an SRS Malfunction appears on the instrument cluster, and Xentry says "The squib for the Fuse'On-Board Electrical Network Line' has a malfunction. The electrical lines have a short to each other."
I checked the Pyro fuse on the positive battery terminal for continuity, and it seems to be good.

Rickman30

Seems you have already connected the dots between the lights and radio via CAN, two things with issues. Seems your radio/COMAND head unit is disrupting CAN signals to the SAM and affecting circuits there, namely the tail lights. So instead of unplugging the CAN bus as described, unplug radio directly, then ensure rear lights come back to life. If so, you need to replace or repair radio/COMAND unit. If not, you will need to unplug each module independently till lights are functional again.

Rickman30

This can also be affected by the CAN bus. A corrupted signal will disrupt communication at the gateway module, the BCM then assumes it s at fault.

Once you find the faulty module by unplugging one at a time, you can leave it unplugged. Save a copy of all codes, then clear the codes, restart car, then rerun code check to see what comes back. If the SRS doesn't return, that was the issue. Otherwise that will be a completely separate diagnosis.

W212er

I've removed the headunit from the car multiple times, but the lights don't start working the only thing that seems to do is make the car unable to be locked using the key fob.

W212er

It's my understanding that each of the connectors that go into one of those CAN distributors is connected to multiple modules, so how would I narrow down which module exactly would be the problem?

juanmor40

CAN fundamentals https://www.diagnosistips.com/automo...ademy/can-bus/

Rickman30

I’m sorry, I tried to make it simple. When you unplugged the bus, you stated several systems or components quit working but the lights started working. Correct? Out of all those that quit, unplug one at a time to narrow down to which one allows the lights to work. If none, look at your diagram to see what you are missing that is also on that leg of the CAN line, and unplug one at a time to verify which allows the lights to work.

Hope this helps.

CaliBenzDriver

We are going through process of elimination to pin point what module colapses the bus...

This right here says CAN-B KEYLESS Module located near R-SAM.

W212er

Thanks for all the replies, I'm currently out of state so I won't be able to test anything until this Saturday.

I do recall that either the Keyless Go or Keyless module reported something about the Bus being "Off". I believe the Keyless GO module was an option so does it replace the other Keyless module or is it in addition to it. When all CAN connections are connected the car will unlock by putting my hand on around the door handle, what module does this suggest isn't working properly?

Rickman30

The code should read something like this, "______ has lost communication with____or missing messages" This indicates the CAN signal is missing or corrupted. When the CAN is restored it will resolve the code itself.

This shows a bad CAN signal https://4.bp.blogspot.com/---BBiyGsW...CAN%2BWave.jpg

This link shows a healthy CAN signa lhttps://www.garagelube.com/wp-content/uploads/2020/06/CAN-Waveform.jpg

These two examples give examples of why using a scope is really the best and only way technicians use to locate and repair modules disrupting CAN circuits. Even if you purchase a $200 UScope from ASEwave, this is better than guesstimating which module is causing your issue, because it may be a connector with terminal fretting, a wire insulation rubbed through, or water corrosion, which could falsely condemn a perfectly good module.

Hope this helps.

S-Prihadi

This can bus test is quite a complete one for what-if scenario :




First simple check : use the ohm meter to see a 60ish ohms or 120ish ohms or some very low ohms ( shorted ). Modules must be sleeping for this test, not awake.

Rickman30

Good video S-Prihadi. a helpful primer to CAN testing on a scope.

I was taught to disconnect the negative terminal of the battery before this test.

In most modern cars, there are two 120 ohm resistors, one in the CAN controller, SAM, BMC, SCM, etc...The other will be in another module on the same circuit. you should see 60 ohms only, if you see 120 ohms or zero or if the readings fluctuate, it means a fault in the CAN circuit.

This video, is good, however it does not show all types of CAN faults and how those faults affect the data packets. So be aware of that. Simply put, if the data packets in the signal are clean sharp lines with near perfect 90 degree corners, it's a good CAN signal, any deviation in the signal, small or large, is an indication of a fault.

If you are using a meter directly to connectors, be aware you can ruin the pin terminals if pushing the test leads into the terminals too hard. there is a specific amount of drag on the terminals to prevent terminal fretting, a common cause of CAN faults.

Hope this helps