Hello,

My E350 4Matic Wagon had a diagnosed communication problem with both rear ABS sensors, due to which it was capped at 38 mph and ABS and EPS were off because of these. I replaced the sensors and it goes without this speed limitation now.

I saw that ABS and EPS are controlled by the AUX Battery which I replaced, it was 9 years old. I also had some key recognizance problems because of that as well.
I also replaced the main battery, so both batteries are brand new.

Problem:
Car refuses to start. It seems like it's got enough juice. The key is recognized.
When I turn, nothing happens. It unlocks however the break pedal.
It warns me that ABS and EPS are deactivated.
It says don't forget your key
And lastly, if there is any help, the blue high beam light is ON in the dash (although it's not physically activated from the light controls).


Any miracle RESET procedure?

Thank you all.

 

check codes
Is it possible battery clamp is loose?

 

Unfortunately I'm not equipped for codes
No. I verified, it'S very solid.

 

You're going to go around circles without a scanner... even with live codes it can still be a guessing game.

The easy reset you can try :

1. charge/float batteries
2. disconnect both bats for 5mn
3. scan the car OBDII

CLUES...:
Quote: "blue high beam light is ON in the dash (although it's not physically activated from the light controls)."
- - Sounds related to a damaged F-SAM or your iCluster bus not working... or simply a drained battery consistent with no start condition.

 

You REALLY should get a scanner owning any modern vehicle.
1 thing you can still do before getting one, find how to display car voltage on the cluster and observe it during starting procedure.

 

Unfortunately it does not work.
I bought a scanner, and I also borrowed one from a friend.
Both scanners indicate "turn ignition ON".
Can't read codes otherwise.
Which is my main problem

 

Careful, the scanner "turn the ignition on" means to have the key in the "ignition position" not the engine running

In your original post, you mentioned the key was recognized and I understood you can rotate the ignition to positions 1 and 2, correct? It just happens the car does not start, correct?

 

It is turned in the ON position.
that's why I said in my first messages that messages are displayed = not mileage but EPS, ABS off and Airbag off

 

What is your battery voltage?

 

From the description sounds like ignition switch is having bad contacts. If the knob turns, the key recognition works.
I have $49 Autel knob, who makes nice troubleshooting page, showing each component status.

 

I found the culprit. The rechargeable AUX battery emptied itself inexplicably, although it was at 11.4V when I bought it. Also it seems it is not fed from the main battery in order to charge, at least not while the car isn't running. So it's either charged from the main batt when it runs or from the alternator.

Also the fuse on the AUX battery was done.

Thank you all.

Good thing to know: start is fully controlled by the AUX batt. If that's out, you can't start.

 

Your experience highlights why it is good practice to float both batteries... keeping voltage up with a (CTEK/Benz) smart charger will alleviate slow drain issues and prevent high charge rates.


Easy access to float both batteries

 

The aux battery is charged by charging module and doesn't have direct connection to main charging system.
You did not say what MY you have, but if you have small aux battery in the dash, this is for emergencies only and it is charged only for short time after engine start, then disconnected from the system.
Strange the fuse burn in the process.
Either way, the battery that is disconnected from the system going down means the battery was bad. I had 2014 model with ECO battery sitting for long months and never charged AUX battery, not having any problems. My diesel restarted on 1st turn after sitting for 14 months.
Good to hear you got it solved.

 

Nice to hear you solved your problem.

Would you mind elaborating on which year is your car? Is the AUX battery behind the dash, or in the trunk?

For clarification, testing on my 2014 W212 (not S212) E350 shows the AUX battery is after the BCM (Battery Control Module seen it the picture from CaliBenz above) and it is isolated from the main circuit unless the BCM allows it. It is my understanding the main cable coming into the BCM is coming from the main battery, and the BCM output feeds the AUX only when "it pleases". If you measure the voltage between the AUX posts, you should measure @12.xV for a good battery, and once the car is running you will measure for a very short time 14.xV from the main+alternator, and then back to the 12.xV. Once the "brain of the charging system" decides to charge it, you will measure 14.x again. I have measured it after a short ride w/o turning the car off, i.e. park, open the trunk, and measured it. Once the car is turned off, the whole cycle starts all over again.

What I would be worried about, and would monitor, is the source of the blown fuse. Either there was a short during installation of the newer AUX battery (great! one-time event) , or the battery shorted itself (bad luck and drained ), or something else (not so great ).

Enjoy your ride.

 

It's a 2011 E350 4Matic Wagon.

About location and type

First, on a YouTube video it mistakenly shows that the Wagons had the other kind of AUX Battery (with drilled terminals located on the longer side) and that's supposedly in the trunk (right-rear corner)
Apparently that's true for most Wagons, but not mine, probably because it has the Harman Kardon subwoofer taking up space.

So yeah, it's behind the dash, it's the batt with the two terminals located on the shorter side.
Easy job if you dismantle the cover above the pedals (it has 3 simple screws) because you can have one extra hand reaching from underneath.
I've seen a video with a guy doing it only from the side. It felt impossible to me.



In the pics:
the two possible kinds

 

Strange to hear that bad emergency battery disabled engine start, but several times I wonder what MB programmers smoke for breakfast, so nothing really surprising.

 

Also,
I paid my battery 9$ US.
$136 at the stealership.

Did it knock off the fuse because it's not original? I doubt it. We'll see... 3 days in, still perfect so far.

 

Since you installed it from below, perhaps it touched something. Hopefully, just a one-time event.

 

Yes, I'm sure it was me.
Maybe even a short.
It's not easy, you have little room to play with it.

 

fyi, 11,4 volts is a very deeply discharged lead acid battery. fully charged at room temps, it should be around 12.6 volts, anything below 12.0 is flat.

small aux battery in dash vs larger one in the trunk is a function fo whether or not your car has eco start. my 2016 wagon has the larger one in the back AND the hk subwoofer.



the battery and rear SAM are under that piece of molded carpet that is sitting on the spare in the pic.

 

You're welcome.

 

Your tool holder is awesome compared to my plastic "rattle box". Is this a wagon special or the same in sedans after certain year?

I assume it has a plastic nut underneath to hold spare in place?

 

yeah, there's a hub nut to hold it securely in place.

I dunno about any other years, our previous Mercedes wagon was a 1994 W124 E320.

 

I have the same tool holder in the 2011 Wagon.
It's styrofoam.

 

'11 E350 wagon has the styrofoam tool tray, wheel just sits in spare tire recess. '11 E550 has a plastic tool "bucket" that threads into spare tire floor tray.