Good day all this is my 1st post on the board and look forward to all of the replies!

I’m an avid DIY and I can’t see paying someone to do something that I can do myself.

But to the point. The Auxiliary Battery Malfunction message has illuminated on my 2010 E350 (W212). The issue is I can’t find the location of the Aux battery so that I can change it. Does anyone know where the aux battery is located? The only battery I’ve found is the main battery under the passenger side of the hood next to the cabin air filter.

Where is the Aux battery located?

 

Try looking in the trunk beside the spare tire.

 

Thanks for the reply Tj I looked in the trunk under the spare tire and didn’t see it I look at the back drivers side and only send a compartment for replacing the tail light bulbs and on the passenger side the 1st aid kit and the rear fuse box. Although I could overlooked it.

 

Well its the Auxiliary Battery for the automatic transmission. I have no idea where it is or what it looks like. I am sure if you call your dealerships service department they would be glad to answer a simple question like that.
Come back and let us know where it is when they tell you.

 

There is a 1.2AH backup battery to electronic transmission gear selector below instrument panel part # 000000004039 lists for about $45. Replacement involves removing covers to left side and bottom of dashboard on driver’s side. Check your PM.

 

Called MB today, 11/25/2013, and spoke to the service Mgr Scott. Advised him that I was getting a service message on my dash that said, Auxiliary Battery Malfunction. He advised me that the auxiliary battery was under the passenger seat & would be replaced, at no cost to me, if vehicle was still in warrantee. (Not more the 48 months old or over 50,000 miles) Will advise further after service is done. Hope this helps some one who has the same problem. RBM Cave Creek, AZ

 

Advised by service mgr, Scott, that the auxiliary battery is under the passenger seat and would be replaced, under the warrantee, if within, (48 months / 50,000 miles)

 

Battery is actually under the instrument cluster not under the seat.

 

Was advised by MB service mgr that the Auxiliary battery, on my 2010 E 350, was under the passenger seat. WRONG. With the information & diagram, sent to me, from Greg. I found it under the driver side gauge cluster. Thanks Greg.

 

 

Have dealer check VMI to if your vehicle is included in Service Campaign 2009110003 released JAN10 – affects VIN A000977 to A092538 may need to update front SAM https://mbworld.org/forums/3917691-post8.html

 

Hi there,

Thanks for attaching the pdf file. In my country it is not free of charge. They said it is considered a consumable item and customer has to pay for it. So, I bought the auxiliary batter, it costed me USD 85 and I replaced it myself.

Read the pdf file and here are some notes that would help:

1. The auxiliary battery is actually behind cover 1.
2. You better use a panel removal tool.
3. After removing cover 1 and then cover 2, unscrew screw/bolt 5. Basically screw/bolt 5 is what is holding the auxiliary battery.
4. While unscrewing screw/bolt 5 try to hold the battery from the back.
5. Unplug 6 and 3.
6. Take out the old battery and put in the new one.

Do the steps above in reverse.

Thanks again for attaching the pdf file. It helps a lot.

Thanks,

 

Quick note: I had my Aux battery die on me this past week. I had just bought my E550 three weeks ago, and when we got some cold days (well, cold in terms of Florida) it started to give warnings about malfunctioning. Basically it was an edge case.

Took it in today to my dealer here in Gainesville, and they replaced it free of charge despite it being a wear item that would normally have to be paid for. They stated that since I had only bought the vehicle three weeks prior that they were going to cover it in this case, even though it didn't show up during CPO inspection.

Frankly, i am quite impressed with that. They didn't have to cover it, but they did given a reasonable situation.

 

Where does the AUX battery live?

My previous car was a '05 E500. I knew where both batteries were, and I assumed all the E class cars had both the main battery in the trunk and the aux under the hood.

But when I started shopping for an '11 or '12 E550 I found that some...well, most of them did not have a battery in the trunk at all.

My '11 E550 does have the main in the trunk. It must come down to specific option combinations.

 

272 (350) main battery is located in engine compartment, 273 (550) located in trunk. Additional is located left side of dash, see link http://www.google.com/url?sa=t&rct=j...,d.cGE&cad=rja

 

I looked at a MY10 E550, and a MY12 E550 and I am almost positive that there was no battery in the trunk of either. In fact, I looked closely to see if the battery had simply been removed from the '12 but there were no cables either. Nothing.

 

See attachment

 

Huh, really have me scratching my head now.....

 

OK... let's be explicit here:

Main battery:
(the one that every car with an internal combustion engine has had since the early parts of the 20th century)

E350: Under the front hood
E550: In the trunk, next to the spare tire under the carpet.

Auxiliary Battery:
Powers things like automatic transmission functions, cruise control, etc.

In the cabin, driver's side, under a panel near the driver's left knee. It is accessed through a panel that can be reached when the driver's side door is open.

 

Maybe not so explicit??

Here is a 2011 E550 P2, etc. trunk. That looks to me like where the main battery could have been in some models/years??

 

Well... isn't that special?

I should really do better research than I did, eh?

My 2010 definitely has the main battery in the trunk, and quite frankly I have no idea how they managed to fit it up front in later models. It is a monster!



Battery compartment for 2010 E550.

 

EPC shows:

MY 10 & 11 e550 (273 engine) up to 8/10 trunk, to 4/11 engine compartment; 4matic – engine compartment

MY12 e550 4matic (278) - engine compartment

 

Well, maybe the real story is, when, and exactly why, did MB decide the battery could be moved to the engine compartment?

Obviously, at some time in the past (before my build), the battery was in the trunk, otherwise the obvious battery tray, with drain, would not be there in my car.

Therefore, at some point MB must have decided that they wanted the battery in the engine compartment. WHY? WHEN?

Now my experience, which may, or may not, be relevant: At about 20,000 miles my battery crapped out. Had to call roadside to get a jump, and they took it in and determined that some strange fan thing (NOT the big cooling fan issue) had run over night due to some software bug and drained the battery.

OR, OR, OR, was the problem really that when the crack engineers decided to move the battery to the front they also had to install a smaller battery because of the tight, hot space up there, thus the lifetime issue???? And, thus, later, they moved it back to the trunk.

Car batteries are really big current hogs, and the connection to the point where the current is initially broken out and distributed, has to be a really big heavy piece of cable --- and it needs to be short, or a hell of a lot heavier. I wonder of the initial trunk positioning, with the long cable to the front of the car, presented electrical problems, kind of "OHM's Law" stuff --- pretty basic, unless some engineer is trying to stretch the laws of physics in order to get a raise.

OR, OR, OR, was there some problem with safety, with all that electrical power (HUGE!) with potential sparks and fire, on top of the gas tank, in a rear-end accident, not to mention sulfuric acid flying everywhere.

As with so many things with the relatively recent Mercedes autos, there are weaknesses, aberrations, and just plain bugs, that seem to be left kind of secret, as we consumers, who have put out only $70,000, have to deal with them and argue with dealers who are less than knowledgeable or just plain obtuse. If I could bill MB at my current billing rate for time spent dealing with this crap, MB would have simply refunded all my purchase price a long time ago. Unfortunately, the only entity that gets to bill at billing rate is Mercedes!

If I seem a little upset, I will refer to, just for one example, the E550 brake situation, as I wait for the fourth iteration of pulsing (and intrinsically unsafe) front brakes.

 

My response, obviously, prior to Konigs'.

 

Whew, I feel better now.

Engine compartment vs. trunk. The reasons will be many and varied. Cost, weight distribution, and packaging are, I would guess, the primary drivers.

My '05 E500 had a gigantic one in the trunk. Wifes 330CiC has it's only battery in the trunk. Neither were a problem, ever.