Jimbob1

I am getting the Auxiliary Battery Malfunction on my 2014 GLK350. It is still under the 4 year warranty. I am new to MB and searched a LOT for some info on the Aux Battery and it is still a mystery. I found what I think is the main battery under the hood on the passenger side but can't find the Aux Battery. Can someone tell me where it is?
Thanks in advance.
Jim

JohnnyC

It is in the boot, under a cover, which will require 10mm hex, Torx 30, and Torx 45.

Mmr1

I'm just guessing but I think It should take you 10 minutes to replace , I've heard of a 250$ charge for this, it can't be more than a 50$ battery for its size. I opened up the back to find it , it was easy.

Jimbob1

Johnny and MM-Thanks a lot. I almost went blind looking in the operators manual for something on the message and the battery and could find nothing. Then went to the forums and found a little but nothing on the location.
Jim

Jimbob1

Just a FYI.. Dealer replaced the Auxiliary Battery (part # 211-541-00-01) free under warranty.

ZZGlk

You might want to keep an eye on the voltage to the aux battery. That battery's primary purpose is keeping the ECO components working. The main draw is the ECO transmission pump. If you use the ECO feature frequently, I can see a possibility of that battery dying before the warranty is up. If you don't use ECO, that battery should be good for a lot longer than the warranty.

Frequently, the aux battery relay fails and this would keep the aux battery from getting a charge and kill it much sooner normal. I would hope the dealer would check the aux relay, but I never count on anything from them. A periodic check of the aux battery voltage would let you know its being charged correctly.

Jimbob1

ZZ--That made perfect sense to me. I went to the garage to do the 5 minute job of removing the cover and checking the voltage. I am still trying to get the cover off. It appears from Johnny C's picture (and my own deduction after removing the 2 10mm nuts) that the plastic plate running across the boot has to be removed also. I removed the one screw that was just in front of the "latch loop". But now I am stumped and need some guidance.
Can someone tell me how to remove the cover from the auxiliary battery?

ZZGlk

First, take the boot lid all the way off. It's lots easier to clear all the pieces with it out of the car.

Next, there are 3 torx bolts that have to come out, as well as the two 10 mm nuts. One is in back, in plain sight, near the aux fuse block opening. The other two are hidden underneath the rubber liner in the rightmost section of the tray. Once you remove all of the bolts and nuts, pull up on the forward portion of the plastic tray. Then, gently lift the rear section of the tray until it clears the protruding 10mm bolts. The lip of trim piece for the back door overlaps the tray, so gently lift up on that and then the whole tray should slide out from under that back lip. Not the best design work Mercedes has ever done, but once you find all the fasteners and do it once, you'll remember the trick.

PACIFICMAN

Hello all,
I have a 2014 GLK350. a couple of months ago I began to get, rarely, the "Auxiliary Battery Malfunction" message. The ECO system continued to work, but over the months the messages came more frequently. Becoming daily, all the while the ECO worked, GREEN ECO on dashboard. I searched and read the various threads. I felt the Battery was the culprit and I had it tested. It had voltage of 14.4(my meter) when I pulled it, then 13.6, BUT only 54 CCA.(Spec. 200 CCA). It is the original Batt. made in 12/14 so I didn't feel like it owed me anything and I replaced this week with a modestly priced AGM battery. The message has not flashed BUT the ECO restart has only fired once and the YELLOW ECO is showing on the dashboard, except for the moment of the one restart. I now believe it was a symbiotic failure of Old battery hastened by Intermittent Malfunctioning Relay. My Questions:
1, Is there "reset" process for the ECO battery replacement? I can find no reference to this....
2, Is there a way to test / trouble shoot the Relay?
I am pretty handy and have done all the maintenance on my 3 MB's, but my Electrical savvy is light.
I am willing to go the money on the relay(costly) but I would like to know better if I'm on the right track...
Thanks in Advance for any Advice, Tips or Surefire fixes...


PACIFICMAN,
SoCal

Mmr1

I asked the dealer why my green echo light rarely comes on, he said many parameters must be met before it goes green. So something is off spec.
Do you use Echo, because stop start wears out the starter and you are restarting the motor after oil has drained back, not good.
I think it puts extra wear on the motor and starter, I never use it.

ZZGlk

If your existing battery read 14.4 V when you pulled it, the relay is probably working fine. Don't worry about the CCA on the aux battery as it doesn't crank anything and is only 12 AH. All the relay does is keep the aux battery connected to the main battery for charging and disconnect the main from the aux when ECO is operating during stops. It's got a lot of logic that controls it, so its almost impossible to do a definitive test without MB equipment. The main battery must be at a certain level of charge for about 20 minutes before the relay closes and allows the backup to charge. Is your main battery original as well? Might not hurt to have it checked if so. Mine only lasted about 3 years.

As far as the ECO not coming on, there are a lot of variables that are looked at before that works. The owner's manual has a list of all the things that must be satisfied before getting the green light.

Its pretty hard to troubleshoot the ECO system and the Aux battery without MB diagnostics. All you can do is test both batteries and check the list of items needed to satisfy ECO. If one of the items you need for ECO is working correctly but sending a signal that its not, you're pretty much out of luck. I suspect that MB doesn't have good procedures and tests for ECO and Aux battery issues as they usually just swap out the battery or batteries and the relay and see if that works.

I tend to agree with Mmr1, ECO will cause more wear on the system than its worth. I trained myself to reach over a switch it off every time I start. My Aux battery is now almost 8 years old and going strong because ECO never gets used and the Aux battery is always fully charged.

Jimbob1

I agree with MM and ZZ. I try to press 2 buttons when I start either one of my vehicles. Start and ECO (to turn it off). Too much wear and tear on mechanical things in my opinion. My battery was changed out for free under warranty.
There are several utube videos on how to test a relay if you have a multimeter.

Mmr1

My 2013 is at the point it rarely , if ever goes green and activates, which is fine for me since I don’t like what “stop- start” does to the motor systems. Being Increased engine and starter wear.

PACIFICMAN

So, To update my Aux. Battery situation. I have driven the Car more and longer in the last few days and the ECO system has begun to activate(GREEN ECO) more often and more as I recall. I've come to feel the main battery may be less robust than I thought, causing the ECO logic to activate less. I tested it and it showed 12.8v which works to start but seems low-ish given the high charge rate. In any event I'll have it tested to determine amperage(it is still well under warranty) and proceed from there. Thanks for all the Help!

ZZGlk

Mid-city Engineering has a mod that will let you default ECO to off. I was going to look into that, but have gotten so used to hitting the ECO off switch I don't even notice it anymore.

Testing the Aux battery relay with a multimeter will tell you if the contacts are good. The real challenge is figuring out if it's opening and closing when it should. The logic that operates it is complex and I haven't ever found more than a cursory list of things it considers when switching. I know it looks at the following from observing when its working with my datalogger.

1. State of charge of main battery,
2. Time since start.
3. Aux battery voltage
4. ECO on or off.
5. ECO logic satisfied - Green Light.
6. Engine running or stopped.

I am sure there are other logic inputs, but haven't ever found a full list. Remember, the Aux battery relay is also used to isolate the main battery from the rest of the car when stopped with ECO operating. That allows the AUX battery to power things like the transmission pump and ECO logic functions while keeping the main battery from being discharged.

Note: 12.8 volts on an AGM battery measured when the battery is at rest for an hour or so indicates 100% charge. If you measure 12.8 volts immediately after shutting the car down, that's probbaly too low. It should be more like 13.4 volts right after shutoff and 14.4 volts when the engine is running.