I have a 2015 E400 4matic w212. It has lots of little electrical issues that happen randomly. It also has some other mechanical codes that haven't set a CEL yet. I've cleared the fault codes, but they eventually come back.

I'll start off with the electrical issues:

N93 Central gateway:
U103888 Communication with CAN bus has a malfunction. Bus off.
U103811 Communication with the diagnostic CAN bus has a malfunction. There is a short circuit to ground.
U118300 The diagnostic CAN network management is unstable.

N69/5 KEYLESS GO:
B1F8D14 The low sensor of the rear switch module has a malfunction. There is a short circuit to ground or an open circuit.

N123/4 mbrace:
B15D814 The cable for audio muting has a malfunction. There is a short circuit to ground or an open circuit.

Pretty much what I'm experiencing is keyless go randomly not working and the speakers going mute. The lock/unlock functions on the door handle randomly don't work but pressing the button on the key fob works every time. Occasionally it will throw a "replace fob battery" warning on the IC. I already replaced the battery, and it still does it. The speakers randomly go mute. Command is working the way it should but no sound will come out of the speakers. The only way to fix it is to press the volume up button on the steering wheel while driving and it will randomly start working.

Does anybody know where I should start with diagnosing this electrical issue? I believe all 3 codes are related but I'm not sure if it's a module malfunction or if there's actually something damaged?

It has some mechanical codes too but no CEL:
P029900 The boost pressure on turbocharger 1 is too low.
P254000 The signal for the pressure sensor of the low pressure fuel circuit is implausible.

These mechanical codes cannot be cleared. They instantly return. Is this concerning? I notice a lot of metallic rattle when driving at low speeds in this car. Possibly from a worn wastegate. Does this need to be addressed or should I wait for it to turn into an actual issue? As far as I can tell the engine runs perfectly fine and there's no CEL.

 

That's a serious basket full of faults you've got your hands on!!

> You have noticed your KeylessGo module is operating marginally... that is a standard fare.
To work properly the module needs to be all resoldered or replaced new again.

> The P029900 The boost pressure on turbocharger 1 is too low.

It's likely the check-valve inside vacuum pump.

> P254000 The signal for the pressure sensor of the low pressure fuel circuit is implausible.

Double check the status ACTIVE OR STORED?? Fuel tank pump or sensor may be fixing to quit.

These faults do not clear while they are still actively present.


> Good deal...
U103811 Communication with the diagnostic CAN bus has a malfunction. There is a short circuit to ground.
U118300 The diagnostic CAN network management is unstable.

These are actually ghost faults caused by some scanners over the CAN-D.
Not a problem: Ignore reset/clear.

 

Could it possibly be caused by a failing aux battery? I dont have any warnings for it but keyless go and command start acting up when it's cold outside. However, eco start/stop works fine.

Key on engine off, command will go black randomly. Starting the engine fixes it.

Typically when you disconnect a vehicles battery it will set a bunch of electrical codes like this. It makes me wonder if the aux or main battery are just worn out and dropping voltage to all of these modules?

 

The code for the low pressure fuel pump is stored. Clearing it makes it return instantly. Same with the turbo code.

 

Do you want to diagnose your unstable tank pump low pressure ?
Read tank pump pressure sensor from the pump control module with engine idling.

Be sure to clear ECU module under these conditions:
IgnKey=ON + Engine=OFF.

Turbo code returning with engine Off is odd... possibly user error?

 

Welcomed, you've discovered ... your chassis operation is sensitive to low-voltage power **

Many details are practically tweaked to grow into opportunities - This is generally well but does not means ppl who can read must endure without self-help.


**: there may be ways to fix some of these issues...

An easy way is to cancel dynamic voltage to disable "drain by driving" 90Amp/15V battery toaster.
It's experimental and not any WIS standard procedure.

 

Yeah, the W212's electrical system can be a bit finicky, had a friend's 2021 S-Class with persistent issue where the nav screen would go dark and require a reboot, ended up being a faulty iBRCE sensor. Not sure if it's related to yours, but might be worth looking into.

 

What's the iBRCE...
What is preventing this feature to run satisfactorily from the get go ??

It's interesting to realize that CAN features long nested loops to be glitch sensitive vs. equal Star branches to be stable no matter what.
Robert Bosch wrote the CAN-Bus specs

 

I may have discovered my issue. My car was rear ended before I bought it and the knee airbag deployed. After seeing photos of other people's cars I realized a bunch of the lights on my dash aren't working. There's no telling what wires the knee airbag destroyed when it went off.

What i do know is that the LEDs on the push to start, parking brake release, and headlight switch aren't working. I guess I will have to take the dash apart and start digging through wires.

 

Hands off your wiring!!!
Diagnose your display first to KNOW what you are looking for.

The wires and connectors are undersized to be fragile to the point it's best not to move them arround more than necessary.

You can direct your attention to the IC-Display module for interactive testing.

 

I'm talking about the LEDs inside of the physical buttons on the dash, not the IC. There must be a wiring harness in there that was destroyed by the airbag.

The dash on the driver side is 2 pieces. The upper half above the steering wheel, and the lower half below the steering wheel.

None of the buttons on the lower half of the dash are lit up. Probably because they fixed the wiring for functionality and were too lazy to fix the LEDs.

There was a lot of shortcuts taken when fixing the crash damage on this car. It wouldnt surprise me if they didnt repair the wires correctly.

I wonder if theres a module or sensor for keyless go under the driver side dash?

 

-- The IC-Displsy "dashboard" is an half-smart module with built-in private network gateway.
-- Under that is the steering column
-- Under that is a A/C duct and footwell upper cover.

I'm not familiar with what the lower knee airbag is setup to destroy on the way to its Max opening.

An MB compatible scanner will show you live what you are dealing with... bit by bit.

Working upside down under the dash on your back requires serious motivations... you'll see.

 

What sort of scanner do you have? The typical FLAPS jobs don't have the ability to get all that deep.

Also, before you dig, check where your utilities are.

https://charm.li/Mercedes%20Benz/201...%28273.970%29/

This is for my particular year/trim, you'll have to back out in the breadcrumbs up top to get to yours. The wiring diagrams are in there, and they'll help you figure out where to dig for what boxes. Combined with a proper scanner, and in your case possibly a multimeter, this should be a 95% solution. I was able to diagnose a short in my adaptive suspension computer (not the strut or harness as would otherwise be suggested) with this combo.

 

I might need a copy of WIS. That website is great but it doesn't go up to the 2015 that I need.

I am running xentry for my scanner.

I have no idea how things could be shorted. Im also not sure how the car is functional if the central gateway is shorted and turned off like the code says. The car only had minor body damage and the interior is pristine except for the knee airbag under the steering wheel.

 

what is Xentry showing you ?
You said gateway is bad...
its in the hot engine room.

 

Xentry is just showing me the fault codes in the original post. CGW231 works fine but it does have those codes and the random command and keyless go issues.

I just found out it's inside of the fuse box under the hood. Ill check it out but theres no reason why it would be damaged.

 

At this stage it seems KeylessG is near the top of your list of concerns.

It bugs CAN-B that bugs CGW that drains batteries while parked...

Keyless module can be replaced, refurbished or resoldered.

 

I believe I have found the issue. I decided to check the fuses and found the absolute dumpster fire the previous owner left. Multiple fuses were missing and it had multiple incorrect fuses. One of the missing fuses went to the keyless go module. There was 5a fuses in 7.5a slots. 20a fuses in 10a slots. It was all wrong.

I just replaced all of the fuses with the proper ones and verified that all fuses were present. After fixing this keyless go works perfectly fine.

I need to do a few drive cycles and scan with xentry again but I believe it's fixed now.

 

That's great discovery work right there.

The last guy who worked on your fusebox could not fix it. He managed to mixed up a bunch of fuses looking for luck - He couldn't get any with precisely crafted KeylessG module.