2014 W218 Dead battery equals dead windows and mirrors - Mercedes-Benz Forum
 
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post #1 of 10 (permalink) Old 09-28-2018, 10:01 PM Thread Starter
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2014 W218 Dead battery equals dead windows and mirrors

Greetings
I am hoping someone can shed some light on the following situation:
Vehicle in question is a 2014 CLS550 (W218) which worked perfectly fine UNTIL I killed the battery. Now the windows and mirror adjustments don't work.
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Battery was trickle charged (per MB procedure) via jump start posts for 24hrs.
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Battery holds charge, car restarts, no CEL/MIL light but I connect an Autel DS808 (fully updated and running Benz v14.0) and run a diagnostic scan.
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That scan reported a few faults including
FCMU05 low voltage
Comand APS open circuit on each speaker
Central Gateway unstable CAN bus/error in CAN bus message Interior CAN bus turned off.
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Scanner clears codes, verified codes don't come back, life is good until later that day when I try to roll my window down and nothing happens.
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Seems all 4 windows (tried switches on all 4 doors for windows) and mirror adjustments are dead.
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The all up and all down functions on the key FOB do activate the windows
I specifically checked the front SAM module and it looks fine
When I access the front left DCM (door control module) via scanner I can activate the windows (verified all 4 windows up/down within range and don't need normalizing) and adjust the mirrors.
All other mirror functions ( park assist, blind spot, turn signal, and dimming) work fine
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Anybody have any ideas/suggestions before I start tearing into the door panels?
Possible there is still some current or stored fault code only a STAR scanner will be able to deal with?
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post #2 of 10 (permalink) Old 09-29-2018, 07:36 AM
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Something to try, disconnect engine compartment battery for at least 15 - 20 minutes then reconnect in an attempt to reset.
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post #3 of 10 (permalink) Old 09-30-2018, 01:00 PM Thread Starter
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Thanks for the responnse man.
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Sadly I did try that already. I even went the extra mile and disconnected the ECO batttery in the trunk as well as the main battery for a few hours.
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I read in a few places that if you touch the + and - main battery leads together after disconnecting the battery will force some kind of reset. ERRRRR I think I will pass on that one.
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I did more research and am more convinced then ever the issue stems from the error message on CAN bus B (B is interior bus) from the central gateway. Even though the scanner is no longer reporting any fault I think something is hanging around somewhere related to that event in the non volatile memory.
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I omitted in the initial post that the trunk open/close button also stopped working.
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The front left DCU uses both Direct Line and LIN bus lines for communication.
The trunk is on Direct Line S/15 (S15/1 is key FOB and S15/3 is DCU line)
Window and mirror messages run over the LIN bus under the S20 switch group (Windows are S20/s1-4).
The interior CAB bus B manages messages from both the direct line and LIN bus and feeds them to the central gateway.
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Since I can control both trunk open and windows up/down from the FOB that tells me that both the Direct Line and LIN bus are up and functional.
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I believe that narrows it down to faulty communication between the DCU and CAN bus B.
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Grrrrrr, still doesn't tell me how to fix it.
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Anybody know if you can force a reset by pulling a relay?
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I will press on as I can't stand the steelerships and Benz tax.
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post #4 of 10 (permalink) Old 09-30-2018, 01:04 PM Thread Starter
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The front left DCU communication is laid out in doc GF72.29-P-6001FQ
Wiring block diagram for LF DCU is covered in PE72.29-P-2101-97XAA
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post #5 of 10 (permalink) Old 09-30-2018, 01:18 PM Thread Starter
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docs

See attached
Attached Files
File Type: pdf W218 Doors.pdf (1.26 MB, 32 views)
File Type: pdf lf DCU block diagram.pdf (394.0 KB, 17 views)
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post #6 of 10 (permalink) Old 10-16-2018, 05:53 PM
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"I read in a few places that if you touch the + and - main battery leads together after disconnecting the battery will force some kind of reset. ERRRRR I think I will pass on that one".

Touching (for as long as several seconds) the positive and negative cable ends together is simply a way to may sure that all capacitors in the electrical system are bled out. It gives you a more positive reset or reboot. Clearly the batteries are disconnected when performing a "hard reboot".
My first guess is there was a "spike" in the electrical system which probably blew a fuse somewhere. Worth checking all the fuses before testing all the bus networks
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post #7 of 10 (permalink) Old 10-27-2018, 04:48 PM Thread Starter
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Thanks
You are correct about the voltage spike. It caused a CAN bus B (Interior) to turn itself off.
Both an Autel DS808 and knockoff Xentry system (version 07/2018) listed the fault as stored and not current. Both tools would say they cleared the 2 codes in the Central Gateway, but they ALWAYS came back and clearing never made a difference.
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The ultimate resolution for this was to spend fifty bucks for an Xentry online access key. I was then able to download and install an update for the Central Gateway, that finally cleared CAN bus codes out for good. Made no difference in restoring window/mirror control or trunk release.
Left front DCU had an available update, installing that got me drivers window, trunk release, and mirror control back. I had to flash the SCN coding for the other 3 DCU's to get window control back. After all of that the car is back to normal.
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post #8 of 10 (permalink) Old 10-28-2018, 05:27 PM
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Thumbs up

Good Job!
It's getting harder to change a battery these days.
We haven't encountered this particular scenario, but the odds of something going sideways during a battery change certainly increases with vehicle complexity.

At least there wasn't a hardware failure. If you want to see what the Munich crowd is dealing with, Google "Footwell Module.
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post #9 of 10 (permalink) Old 10-29-2018, 05:56 PM Thread Starter
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Thanks, hopefully info on this debacle will solve someone else's problem.
I think its TOTAL BS that charging/changing a battery according to MFG procedures causes these type of issues. It shouldn't require a dealership level diagnostic system to change a battery. I was under the impression that said procedures exist to prevent issues like this. The best or nothing, sigh
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post #10 of 10 (permalink) Old 10-29-2018, 07:34 PM
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[QUOTE=theonlykid1;17593257]Thanks, hopefully info on this debacle will solve someone else's problem.

Hopefully this will not become necessary at every battery change. But thanks to you, a lot of time will be saved knowing what to do and how to do it if needed.
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