2013 E350 Auxiliary Battery Functions
Thread Starter
Junior Member
Joined: Jan 2025
Posts: 68
Likes: 28
From: Denver, CO
2013 E350
2013 E350 Auxiliary Battery Functions
My aux battery is evidently bad as I get the warning message every time the car is started. I did a fair bit of searching and reading on this forum, and the general consensus is that the battery allows shifting the car out of park when the primary battery is dead.
In my case, the brake hold function disappeared when the aux battery died, which I wasn't expecting.
Has anyone documented other features not available when the aux battery is dead?
This post has an attachment showing its location for cars (Thanks konigstiger, RIP):
MODEL 212
without CODE B03 (ECO start/stop function)
without CODE ME04 (Mild hybrid drive
https://mbworld.org/forums/e-class-w...ml#post8255096
In my case, the brake hold function disappeared when the aux battery died, which I wasn't expecting.
Has anyone documented other features not available when the aux battery is dead?
This post has an attachment showing its location for cars (Thanks konigstiger, RIP):
MODEL 212
without CODE B03 (ECO start/stop function)
without CODE ME04 (Mild hybrid drive
https://mbworld.org/forums/e-class-w...ml#post8255096
Out Of Control!!
Joined: Apr 2019
Posts: 11,923
Likes: 6,776
From: Silicon Valley
W212 MY'14 M276-3.5NA @75kMi
AUX SHIFTS ISM
My aux battery is evidently bad as I get the warning message every time the car is started. I did a fair bit of searching and reading on this forum, and the general consensus is that the battery allows shifting the car out of park when the primary battery is dead.
In my case, the brake hold function disappeared when the aux battery died, which I wasn't expecting.
Has anyone documented other features not available when the aux battery is dead?
This post has an attachment showing its location for cars (Thanks konigstiger, RIP):
MODEL 212
without CODE B03 (ECO start/stop function)
without CODE ME04 (Mild hybrid drive
https://mbworld.org/forums/e-class-w...ml#post8255096
In my case, the brake hold function disappeared when the aux battery died, which I wasn't expecting.
Has anyone documented other features not available when the aux battery is dead?
This post has an attachment showing its location for cars (Thanks konigstiger, RIP):
MODEL 212
without CODE B03 (ECO start/stop function)
without CODE ME04 (Mild hybrid drive
https://mbworld.org/forums/e-class-w...ml#post8255096
AUX shifts ISM into Park when low voltage condition is present.
meaning AUX is not to shift out of Park, it automatically shifts into Park.
MBWorld Fanatic!
Joined: May 2018
Posts: 6,600
Likes: 6,547
From: Jakarta-Indonesia
2014 - W212.065 - E400 ( M276.820, 3 liter Turbo) RWD not Hybrid
If your car is B03 start stop version with 12Ah medium size battery at the trunk...... YES, you loose brake hold feature when the AUX battery goes kapoot.
Read here : https://mbworld.org/forums/e-class-w...ry-delete.html
------------------
03. Only a few days back, I get to drive the car and AUXILLARY BATTERY MAILFUNCTION code comes around, I thought...so what, ignore it and see what more can happen.
Little did I know that with current/existing DTC for Auxbattery, I then loose brake HOLD function ...
, I only knew about it during a fuel filter change test drive 
Well, have not driven the car for few weeks now.
------------------
Read here : https://mbworld.org/forums/e-class-w...ry-delete.html
------------------
03. Only a few days back, I get to drive the car and AUXILLARY BATTERY MAILFUNCTION code comes around, I thought...so what, ignore it and see what more can happen.
Little did I know that with current/existing DTC for Auxbattery, I then loose brake HOLD function ...
, I only knew about it during a fuel filter change test drive Well, have not driven the car for few weeks now.
------------------
Thread Starter
Junior Member
Joined: Jan 2025
Posts: 68
Likes: 28
From: Denver, CO
2013 E350
Replaced the aux battery today. Easy 15-minute job. Might take 10 minutes the next time. Brake HOLD function is restored. MightyMax ML1.3-12 from Amazon.
Re CaliBenzDrivers's comment above about whether the aux battery is necessary to shift the transmission INTO or OUT OF Park, do we have any definitive information about that?
S-Prihadi was under the impression in 2022 the aux bat was needed to shift it OUT of Park. https://mbworld.org/forums/e-class-w...ml#post8569254
I don't really care one way or the other, but it would be nice to define that function for someone who does care.
Could it possibly do BOTH?
Re CaliBenzDrivers's comment above about whether the aux battery is necessary to shift the transmission INTO or OUT OF Park, do we have any definitive information about that?
S-Prihadi was under the impression in 2022 the aux bat was needed to shift it OUT of Park. https://mbworld.org/forums/e-class-w...ml#post8569254
I don't really care one way or the other, but it would be nice to define that function for someone who does care.
Could it possibly do BOTH?
Last edited by Dave Doolittle; Oct 3, 2025 at 05:40 PM. Reason: fix typo
MBWorld Fanatic!
Joined: May 2018
Posts: 6,600
Likes: 6,547
From: Jakarta-Indonesia
2014 - W212.065 - E400 ( M276.820, 3 liter Turbo) RWD not Hybrid
Out Of Control!!
Joined: Apr 2019
Posts: 11,923
Likes: 6,776
From: Silicon Valley
W212 MY'14 M276-3.5NA @75kMi
Its not enough to supply electric power, the voltage needs to hold up steady under load current, not drop of a cliff when cranking
Last edited by CaliBenzDriver; Oct 3, 2025 at 10:36 PM.
Trending Topics
MBWorld Fanatic!
Joined: May 2018
Posts: 6,600
Likes: 6,547
From: Jakarta-Indonesia
2014 - W212.065 - E400 ( M276.820, 3 liter Turbo) RWD not Hybrid
Replaced the aux battery today. Easy 15-minute job. Might take 10 minutes the next time. Brake HOLD function is restored. MightyMax ML1.3-12 from Amazon.
Re CaliBenzDrivers's comment above about whether the aux battery is necessary to shift the transmission INTO or OUT OF Park, do we have any definitive information about that?
S-Prihadi was under the impression in 2022 the aux bat was needed to shift it OUT of Park. https://mbworld.org/forums/e-class-w...ml#post8569254
I don't really care one way or the other, but it would be nice to define that function for someone who does care.
Could it possibly do BOTH?
Re CaliBenzDrivers's comment above about whether the aux battery is necessary to shift the transmission INTO or OUT OF Park, do we have any definitive information about that?
S-Prihadi was under the impression in 2022 the aux bat was needed to shift it OUT of Park. https://mbworld.org/forums/e-class-w...ml#post8569254
I don't really care one way or the other, but it would be nice to define that function for someone who does care.
Could it possibly do BOTH?
The design goal is different between small 1.5Ah battery inside dashboard of pre-facelift cars and the 12Ah trunk battery of Eco start-stop battery.
Read slowly below : I will not be able to drive the car , information #3 ......if indeed NOT HAVING 12Ah trunk aux battery power will not allow me to get out of PARK.
Remember, I REMOVED the 12Ah AUX battery, thus not only it is low voltage but ZERO VOLTAGE. But I can drive the car and meaning I can go into or out of PARK.....only Brake Hold is lost.
MB World Stories
The Best of Mercedes & AMG
Manual Mercedes? 6 Times Sindelfingen Let Drivers Have All The Fun
Verdad Gallardo
Mercedes SLR McLaren 722 S Is Extremely Rare Example Modified by McLaren
Verdad Gallardo
8 Classic Boxy Mercedes Designs That Have Aged Like Fine Wine
Verdad Gallardo
Flawlessly Restored Mercedes 190E Evo II Heads to Auction
Verdad Gallardo
Electric Mercedes C-Class Unveiled: 11 Things You Need to Know
Verdad Gallardo
Mercedes EQS Gets A Major Update: Everything You Need to Know
Verdad Gallardo
5 Underrated Mercedes-Benz Models That Don't Get the Love They Deserve
Verdad Gallardo
Mercedes 300D Has Pushed Well Past 1 Million Miles and It Ain't Stopping
Verdad Gallardo
10 Most Reliable Mercedes-Benz Models You Can Buy Used
Verdad Gallardo
Thread Starter
Junior Member
Joined: Jan 2025
Posts: 68
Likes: 28
From: Denver, CO
2013 E350
This is the text I was focusing on:
"I believe that is a car variant with the super small battery at the instrument cluster, which can move gear out of park in Main Battery flat scenario ? Yes?"
"I believe that is a car variant with the super small battery at the instrument cluster, which can move gear out of park in Main Battery flat scenario ? Yes?"
MBWorld Fanatic!
Joined: May 2018
Posts: 6,600
Likes: 6,547
From: Jakarta-Indonesia
2014 - W212.065 - E400 ( M276.820, 3 liter Turbo) RWD not Hybrid
You must be careful when reading about AUX batteries variant in W212.
Later model even use anti-voltage-dip capacitor only and no AUX battery at all.
MBWorld Fanatic!
Joined: May 2018
Posts: 6,600
Likes: 6,547
From: Jakarta-Indonesia
2014 - W212.065 - E400 ( M276.820, 3 liter Turbo) RWD not Hybrid
Well, you asked, thus I explained
You asked in such a curious way.
As I said becareful when reading MB W212 materials, there are some changes from pre-facelift to facelift and final year 2016 production.
Even the CAN BUS channels has changes and this can confuse people who troubleshoot using pre-facelift material while working on facelift cars or vice versa.
You asked in such a curious way.
As I said becareful when reading MB W212 materials, there are some changes from pre-facelift to facelift and final year 2016 production.
Even the CAN BUS channels has changes and this can confuse people who troubleshoot using pre-facelift material while working on facelift cars or vice versa.
MBWorld Fanatic!
Joined: May 2012
Posts: 2,359
Likes: 1,555
From: Pepper Pike Ohio
24 GLS580 '23 E450 4matic 12 E350 4Matic
Remember this is an international forum, for many contributors, English is a second or third language, also these cars are built differently for different markets, so not all function the same.
Thread Starter
Junior Member
Joined: Jan 2025
Posts: 68
Likes: 28
From: Denver, CO
2013 E350
MBWorld Fanatic!
Joined: May 2021
Posts: 2,524
Likes: 2,041
From: US
2008 E350, 2012 ML350, 2014 E350, 2015 ML350
I got am inexpensive TopDon BT100, and it tests battery, alternator, starter. Helped diagnose sisters W211, and two neighbors.
