I get 'Auxiliary Battery Malfunction'. Dealer says that 2017 e300 does not have an auxiliary battery. I can't find one under hood or trunk. Anyone know if that model has aux battery?

 

Might want to try the W213 forum. But it should be the start/stop battery under the trunk lining in your case.

 

There is no Auxiliary Battery in my 2017 E300 Mercedes. There was an "Auxiliary Battery Malfunction" message on my screen. Numerous websites and several videos claim there is an actual auxiliary battery and give instructions on how to replace it. Parts department said there is no auxiliary battery. Dealer fixed the malfunction and service rep said 'They replaced the auxiliary battery'. I asked for the old one and was told 'they have to send it back'. I asked to be shown the location of the auxiliary battery. Mechanic said he replaced the voltage converter under front passenger floor and pointed to a area on the side of the front passenger foot space. He said it was a 'buffer battery malfunction'. Lot of baloney floating around, even with dealer.

 

The only good thing about there response is that they replaced the battery.

 

That's a shame. Dealerships think they need to dumb down their information for customers. Sometimes they do, but when asked for specifics, they should give the details, not a deceptive answer.

 

Hey guys, I have had the same issue as well, I did some research and found this page it is worth reading https://xenons4u.co.uk/blog/mercedes...ion-explained/ .What you'll need to do is just replace old voltage converter and it will solve that warning message!

 

I have an E350e here is Thailand. Can someone tell me exactly the purpose of this battery on my car. Seems, on this model, quite a few are failing after two years. Do MB still use the brake by wire system? What is the best way to make this battery last...put my CTEK on it frequently?

 

For several months AUX. battery malfunction alert displayed. Didn’t notice any impact on car performance as I don’t use Economy mode on my 2014 E350 4Matic. Anyway, hooked up my m/c battery tender to it and after 36 hours, tender indicated battery was charged. Did several errands today and malfunction alert did not appear. In Economy mode engine turned off at stoplight and restarted normally. Battery located next to spare tire.

 

For several months AUX. battery malfunction alert displayed. Didn’t notice any impact on car performance as I don’t use Economy mode on my 2014 E350 4Matic. Anyway, hooked up my m/c battery tender to it and after 36 hours, tender indicated battery was charged. Did several errands today and malfunction alert did not appear. In Economy mode engine turned off at stoplight and restarted normally. Battery located next to spare tire.

As trunk lights are activated when trunk open, I folded down rear seat and ran wiring through rear window to tender which was placed on folded down seat, with leads hooked up to Aux battery.

 

I also would like to know if this “Auxiliary” battery is necessary if one does not use Economy Mode. If it is only necessary for an unnecessary function I will never use, I would like to remove it from the trunk. Your insight would be appreciated.

 

Disconnect the battery negative. See what happens when you drive. Prove to yourself if you need it or not.

 

Thanks but rather than experiment to see what happens, likely several on this forum have the expertise to tell me what will happen if I remove the auxiliary battery. (At this point in my life I am reluctant to conduct experiments that could lead to costly consequences). It is clear that these batteries have lasted only a couple years for some members. That seems unacceptable for me. (I currently have a 2008, BMW Z4 which has the original battery. During winter when it gets little use, I periodically hook up a motorcycle battery tender to it until I get a green light, then disconnect the tender for a month or so.) As the 2014 E350 has a parasitic drain, if parked for any length of time, I also put the tender on that until green light comes on, then disconnect it. Its primary battery and Auxiliary batteries are now 6 years old (40,000 miles.)
Note: A talented, veteran BMW airhead mechanic told me to remove the tender once my bike’s battery is charged, then wait a month before charging it again. He advises against leaving the tender in place all winter.

 

Paraphrasing the consensus of the dozens of previous threads on the mysterious "aux" battery, I don't think anyone really knows for certain what the Aux battery does on a W212. It seems to power some auxilliary functions, like the "Hold" function. When the charge falls low enough, Hold will not be available. I use Hold function when at long stop lights (and I think to use it). Nice feature, I guess. What other functions the Aux battery powers, I don't know.

Some thought that it controlled the "Auto Stop/Start" function. However, in my experience, Auto S/S is clearly controlled by the main battery, not the Aux. Whenever I top-off the charge in the main battery, (or when you replace the Main battery with a new one) Auto S/S function works with a vengeance, unless I turn it off. If this is the function you mean by driving in "Economy" mode, then the Aux. battery is not the culprit.

IMO, the Aux. Battery plays no role whether you drive in Economy mode, or Sport mode. Further, the way Mercedes computers monitor everything in the car, I think you will get MORE "nanny" messages -- not fewer -- if you remove the Aux. battery. Others can share their experiences on this. But I wouldn't expect solid consistency.

 

The function description and logic diagram for this device should be available in WIS. I don’t have access to WIS at the moment or I would look it up.

Doesn’t the device (voltage converter or aux battery, call it whatever you want) control the direct shift function in all MB vehicles? If not, what controls the direct shift function on the W212 platform?

 

Thanks for your response. I do know that stop/start function did not work at stoplights during time auxiliary battery malfunction alert was displayed, whether or not I had deactivated economy mode. Once I recharged the Auxiliary battery, stop/start function returned, so I am now turning off economy mode.

 

i m driving a w205- c200 at first it display auxiliary battery malfunction and i replaced it with the original battery from Mercedes Benz but the massage is still there after replacing and resetting the error ,please advice

I have tried two different battery’s and both of them are working fine in my friend’s car without displaying any massage .My main battery is 5 years old and I haven’t change it do you think it might also have an effect on this?

 

Wrong section to ask. Delete the post, and ask on the right section please.

 

Cross-posting my experience and replacement in my C205 coupe
https://mbworld.org/forums/c-class-c...lfunction.html

 

... follow the link above to see how you may preventively fix this module for $20... before it's too late.

 

Nice idea. Sounds easy enough to do.
Would be good to know if it messes up any of MB's sensors.
The cars are more fixable than rhetoric claims, but they can be finicky.

 

As I do a lot of city driving, the ECO start/stop function is a annoying to say the least. I have to remember to deactivate it every time I start the car, also an annoyance. Frequent activation of this function also, in my opinion, leads to premature failure of the capacitor pack (erroneously called auxiliary battery on the display message). BTW: MB Parts Center calls it a Drive Motor Battery Pack Control Module, even though it contains no batteries. Link: https://www.mbpartscenter.com/oem-pa...e-205905341480
Getting to the point, I was happy when my Start/Stop function stopped working about a year ago. But today I saw that Auxiliary Battery Malfunction display which led me to this forum. I know that if I have MB repair it on a recall campaign I'll be stuck with a working start/stop function again, as this occurred after other (unrelated) service visits which always included "software update" and various "reset" entries on my invoice.
My questions are:
1. Will I cause any harm by doing nothing?
2. Is there any way of deactivating the error display without changing the module? I apologise if these were already covered, but this thread has more posts than I've ever seen on a car forum.

 

Black tape over the warning works.
Make sure you use metric one.

 

The aux battery is not related to the ECO function. Its only purpose is to provide enough energy to set/release the parking brake in the event the main battery dies.

The ECO function is related to the strength of the main battery. The car will not engage ECO when the capacity declines (which happens to batteries as they age).
You'll find that, once you replace the main battery, ECO will start working again. Mine had quit for over 2 years (except for a couple of occasions when I drove the car on long trips),
and a new battery brought it back (with the exception of very cold days).

 

I like this one. Except it would also hide other displays - like digital MPH.

BTW all: MB Parts Center( and others) want $123 (which includes a $15 core charge) for a rebuilt unit. But I got a brand new Hella unit for $95 from AutohausAZ.

 

I have pre-facelift 212's, my auxiliary batteries are in the left side of the dash, I believe all they do is allow you to shift from park to neutral in case of a main battery failure.
On the facelifts, I believe the main battery starts and stops the engine always and the trunk located auxiliary battery takes over the electric load while stopped in eco mode?
Also, there are like a dozen parameters for eco start-stop to work, I don't know them all offhand as I don't have this "feature"

The 213 I think has a capacitor in the passenger side footwell that is used for the same functions as the 212's trunk auxiliary battery, or similar.