Hi Gang,

Some interesting findings I want to share.

01. I have disabled START-STOP function since Aug 2021. Using Autel. Here : https://mbworld.org/forums/e-class-w...ging-algo.html

02. On the 8th May 2022, I noticed that my 12Ah Aux battery ( start stop ) at the trunk was reading 10.27 volts. So ....... that meant no charging is taking place for this baby battery if START STOP disabled...OK noted.
So in 9 months basically I have depleted the 12Ah baby battery. So I charged up the battery and disconnect the positive battery cable, aka DELETING this baby battery from service.
You can read here : https://mbworld.org/forums/e-class-w...el-stupid.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 Aux battery, 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.




Here are the other DTCs reported by Xentry/scanner which are the "package" to the AUX BAT Mailfunction DTC.

Easier view on Autel. Ignore the engine computer DTC, that is from alternator LIN disconnected on purpose, to kill the "idiot-wanna-be-green" YoYo charging algo. See the other 4 DTC.




Look at how MB engineer call AUX battery. Sometime called BUFFER battery and sometime as ADDITIONAL battery ... LOL









Aha...it seems the ESP is the one removing the brake HOLD function.



So, it seems killing of START STOP function using Autel, does not means I can delete AUX battery just like that.

QUESTION 1 : The car program/algo still is monitoring the presence of the AUX battery, but why would it not warn me that it was low voltage (un-healthy ) when it was 10.27 volt ?

QUESTION 2 :
I do not believe brake HOLD uses AUX battery power, because ESP for my car get 50 amps fuse F161 direct from F32 pre-fuse block.
In the mean time, there is only 1 wire going to the AUX battery and has a stand alone fuse of 7.5A.
I mean not power wire for the battery, but smaller wire 0.75mm which can mean sensing wire or a very light electrical load wire ?
Fuse F96 is that wire, it is very small at 0.75mm and is heading to Front SAM.







So I tested what kind of "load" would the wire having F96 fuse be carrying during engine running ?
See photo below, the parallel relay K114 terminal 1 and 3+4 , I jumped with an amp meter to read the load. I wrote as : 2A fuse Jumper / 2A Jump it



During engine start and after it run, like 10 seconds after engine started, the Front SAM started investigating the presense of the AUX battery for a second, the amp meter then read it as 23 milli amps,otherwise it would read zero or 2 milliamps (noise).
Good thing I have the Owon B35T+ multimeter/DMM with bluetooth feature, so I can use my tablet to monitor it from driver seat while starting the engine.
https://mbworld.org/forums/e-class-w...lti-meter.html


Amperage function of the DMM


I did not yet test with brake HOLD feature witth the amperage meter hook up, but I strongly believe no way MB would allow a critical feature as brake HOLD using such a small wire and from so far at the trunk.
Afterall, the ESP has its own 50 amps fuse from F32, fuse F161. ESP = Brake and ABS in our W212.

With the confirmation that the front SAM uses that F96 fuse to AUX battery ( K114 relay terminal 1 ) only as a signalling/diagnostic purpose, I then installed a 2 amps fuse across K114 terminal 1 and 3+4.
This way, any diagnostic signal from Front SAM to check AUX battery presence will be no issue, main battery is the one providing it. I choose 2 amps because the lower rating, the safer it would be. Fast blow if anything goes wrong.






I shall report back if there is any other development.


So, summary for the gang, AUX BAT MAILFUNCTION DTC can also be caused by Fuse F96 blown, aside from AUX battery really gone kapoot.
Becareful if F96 can be get blown, it may be the wire got some sort of damage between AUX battery to Front SAM journey/routing.
7.5A fuse will never be blown from a signaling/diagnostic duty.

.

 

Surya, we like you to be safe so you can be around for TT videos and great investigations. Not having the AUX battery does not help the safety factor to keep you on the road.

The AUX is used as an emergency power supply when the main supply is knocked out (ALT, MAIN BATT, PREFUSE MAIN-K19?).


I am all-in to simplify things out. Before cutting AUX out, I'd try to restore proper charging.

The 2 Amp fuse you added across the AUX relay, essentially connects both batts in parallel, sharing charge and discharge. It's a smart cheat while MainBatt is here but in case the main circuit is ghosted... then steering module is bricked

I think 2x batts in parallel self-discharge each other... So you end up with a flat Main after sometimes, right? How about finding a switched supply to feed your 2Amp "charge fuse".


Plan-B: restore AUX charging.
We assume your AUX charging got messed up when you disabled ECO. Then find a different way to disable ECO without impacting AUX management sounds reasonable. By going that way, you remove the problem created by that ECO programming.
Meaning it's not worth downgrading safety to kill ECO, right?

Let's try to make safe systems better


FUN...
Disconnect Main batt while AUX is in circuit then witness what happens when you open the driver door ?

 

Aha...interesting :

Cali wrote :
FUN...
Disconnect Main batt while AUX is in circuit then witness what happens when you open the driver door ?

I can do that
But I need to becareful and not damage my alternator's regulator, I will explain why when you read further and find make-before-break switching


Cali wrote :
The AUX is used as an emergency power supply when the main supply is knocked out...
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 ?
This variant of non ECO start stop cars do not use relay to disconnect that super small battery from car circuit, that battery is always on-line isn't it. I recalled that was my findings when I had a wiring diag look at it, I believe so.

Surely in Eco start stop B03 like mine, ECO/AUX battery can only be in the circuit ( joining F32 bus bar ) if the engine computer decided so.
This is evident that ever since I killed ECO-START-STOP function via Autel, my AUX battery never get charged anymore, meaning K114 has not been activated since Aug 2021.

It will be actually very awesome if the ECO-START-STOP hack is the version people can buy now via programming , where the ECO button can remember last choosen mode, hence no need to press ECO disabled button anymore
at every engine start. That I am sure, the AUX bat charging session does not get removed from the algo, unlike my crude ECO-KILLED via Autel

However, I am not worried about loosing main battery to a bad/aging battery, that won't happen to my car on the road at the rate I am monitoring its health... he he he.
I would have replaced the battery at 80% health, like I did last year. Bad battery with good altenator while engine is running is not an issue as alternator will mask it, IF bad alternator even with good battery is a big problem
and in 2 hours car will be dead loosing ignition and ECM management from low bat.


======================

Remember those days in early 2021 while we were on "hot pursuit" trying to understand the Smart Charging, I still kept the investigation video on : when does the AUX battery get charged ?
Let's re-visit some.

10th May 2021 test - Minute 3:12 after engine started. ECO/AUX bat is not yet charged by the car.

1 = Alternator Gross Amperage Output at MR8 - F32. 2 = Alternator Voltage output at MR8 - F32

MAIN BATTERY
3 = Voltage and amperage NET charge or discharge to Main Battery, this data come from Samsung Mobis battery sensor at negative post of battery.

ECO BATTERY
4 = Voltage and amperage, only NET charge can happen, discharge is not happening because the car is never in STOP mode, the ECO MODE is available but I never allow it to operate.




At 3:20 then the ECO/AUX bat started to get charged. Charging is Yoyo too, and never exceed 5 amps. Mostly 3 amps and going down to lower amperage. This is a lot for a 12aH battery.

If I want to kill time and learn more, my focus would be on the K114 parallel relay. How does it limit charging current to AUX/ECO bat ?
Is K114 a simple stupid mechanical relay only or it has some sort of component inside it limiting/regulating current flow to AUX bat ?
Is the magnitude of the charging current I am seeing on my test is purely the chemistry of the AUX battery accepting the charging current value, or is there any electronic intervention from K114 ?



See the changes below to the drawing between K114 before facelift and facelift version. It shows some electronic thingy for March 2013 up and not the simple coil of the before Feb 2013.





At minute 3:35 ish to 3:41 the car computer does something unique. It will NOT charge main battery ( see zone 3 zero amps ) but fullfilled all consumption duty of engine management ( see 1 & 2 ), but is charging or F32 is connected to the ECO battery (zone 4 )
I believe this is the time Q diode K19 disengaged itself to analyze further how full is the Main Battery and it is making decision before ready to execute ECO-START-STOP if I choosen so, which I never choosen so.
13.0V as Main Battery unloaded voltage after being fully charged is a normal.

Don't be suprised to see alternator voltage is higher at 13.8V at MR8-F32 compared to Main Battery and ECO battery is 13.1V ish ( still charging )







F32 pre-fuse block in an ECO Start Stop B03 version, we need to visualize it as a 3 zone power supply distribution block. No more pyro fuse F63 inside F32 and K19 Q-Diode now exist in F32.


The switching event for 6 seconds as seen at above screen captures, between Main Battery disconnected from F32 using OPEN mode of K19 Q diode must first and foremost have K114 parallel relay engaged (CLOSED ) for the baby battery 12Ah to be in the circuit.
This is called make-before-break battery switching. Any alternator while producing power, can not have one of its power cable disconnected from its battery because its regulator will be damaged.
In this case it is the positive cable of the alternator at MR8-F32 must first get connected to baby battery ( via K114 activation ) and then and only then Q diode K19 can OPEN / Disconnect.
That is why you see at minute 3:20 K114 parallel relay started to close and only at minute 3:35 to 3:41 engine computer may disconnect Main Battery from car circuit by commanding Q Diode K19 to OPEN / Disconnect.

In yachts, we use special battery switch to select DIFFERENT starting battery bank in event of low voltage to the appointed primary starter battery of that engine and we can later transfer back to primary battery bank while engine is already running.
This switch is a make-before-break battery switch. You can read here : https://www.perko.com/catalog/catego...tery_switches/

Now, the charging of the ECO/AUX battery continues till my meters all timed out. Below is the last few seconds before the fluke 289 at MR8 Alternator timed out.



Values for minute 13:11



So, now my quest is to have the car regain back its AUX/ECO battery charging duty, but still KILL-ECO function permanently ? hick hick hick, seems tough without special programming.
I am not in any need for the AUX battery to exist actually, so there is no burden here. However, knowing more of our car is always interesting.

 

To verify that brake hold is not using AUX battery, tested as per video


UNDER N93 GATEWAY
I was hoping among these 3 choices , one actually is : eco-start-stop button with memory of last choosen mode and stay at that at next key cycle...but they are not.
The HOLD is Brake HOLD. I tried all 3.
SBW I don't know exactly, but I suspect steering-by-wire , my car can park itself using the parking feature ( never try, lazy ) but me must do the gear change.




My naughty Xentry can not do this lightweight coding/adaptations the Autel can on StartStop.The data is semi greyed out, that means we can't change, only reading is possible.
I guess a pass-thru is not NAUGHTY ENOUGH unless online to MB... LOL

 

In the FUN test above...
"disconnect MAIN, keep AUX and open the driver door" - The engine and ignition are both OFF. So there is no surge to ALT or any risk of frying a circuit. I have done this type of disconnect a couple of times.

What happens is F-SAM physically locks your steering at once... using AUX!
It's the modern version of ESL (Electronic Steering Lock). Not a lock on the steering column actuated every key-cycle like on W211... The physical latch is now built-in the electric rack (not the column) and only locks as needed on rare occasions.

The outcome is you find out that F96 and AUX power are used for more than the quick AUX voltage test at every driving cycle.
AUX also backs-up power to the EIS (Ignition switch) circuit to wake-up the car when Main has drained down.

It was surprising that zapping the ECO feature also disables AUX charging control. Let's see what deleting AUX can do....


The post face-lift relay is a modern SSR instead of electromechanical coil & contact.
The power MOSFET transistor conduction can be controlled to prevent surges. It has an equivalent resistor (RDS-ON) that can generate a lot of heat with current. The physical look of this package shows it has minimal dissipation abilities. I have seen how my K114 got heat-stressed by yoyo bug. We can say it only heats up during switching cycles not for extended charge control when charging current goes lower.

(We can clearly say that a weak drained AUX is going to get punched with high current from an unlimited 200A@14.xV source - A good reason to float AUX!)

Have you found the way to disable ECO and keep the AUX charge control??

 

I see, initially I thought you want me to simulate road side emergency where while engine RUNNING ...suddenly my main battery totally gone kapoot...

If while engine is OFF position and I loose main battery as in DISCONNECTED, not a damaged cell scenario where voltage drop like to under 11V, I have done that too often already.
The result is : I will loose total power, just like in any car with single battery.
In fact it was my #1 concern in the past, when doing electrical works and disconnecting main battery...would the AUX somehow still powering anything ? Nope it does not.
In order for AUX battery to be in the circuit, the K114 must first be triggered by the Front SAM before Main Battery power is lost totally. This could be the case if a low battery situation occuring...maybe.
With ECO function still un-touched or after ECO function removed by Autel, I never seen AUX battery ever get connected to the circuit during a total power loss of me disconnecting the main battery.
I do suspension & brake and grounding/earthing work often enough to need to steer manually the steering with main battery disconnected, never the steering get locked mechanically.

My EPS steering does not have any mechanical lock, I know the oldie mechanical lock version I seen on W204...but it does not have any other lock you described as : "The physical latch is now built-in the electric rack (not the column) and only locks as needed on rare occasions." activated so far during main battery disconnect.

Perhaps there are some minor changes during facelift or different region has different component level.


OUT OF TOPIC
You know what, there is a good thing that I did the verification check of if brake HOLD uses AUX battery power or not ( thanks to your thirst for knowledge too )... I get to take a look at the GateWay module in deeper depth.
Last year when I mess with the so called "adaptation/coding", I was too focus on killing the ECO-Start-Stop only

You see, I have option 628 AUTOMATIC HIGH BEAM SWITCH PLUS (IHC+) and I never use it. Well I did try once and it seems to never worked at low speed... that is what I thought and I simply forget about it
because I don't like using High Beam unless I really need to and I will use full blast one manually, not the polite one. Cut the story short............

Only yesterday I realized MB Indonesia never code/activated my 628 Auto High Beam since new...Duuuggghhhh !!!! Crappy QC bastarzdz









I feel like a dork. I should have investigated deeper when I did see youtube video that the A-Light symbol does not show on mine.
I thought it only will show when and if system is ON-ACTIVE, not while it is only being ARMED.... = me ..... LOL
Who would expect MB assembly plant to be this stupid. My car is locally assembled, that means there will be an azz-H who will do good or do azz-H mistakes during coding.... so I happened I got unlucky.

This is not the 1st time I got unlucky from this MB assembly plant screw up.
1st screw up was very expensive , read here : https://mbworld.org/forums/e-class-w...i-am-sure.html

 

Cali wrote : Have you found the way to disable ECO and keep the AUX charge control??
Nope, I don't think it is possible with the crude method Autel simply make ECO-START-STOP goes away.
The AUX charging algo seems to be part of the ECO-START-STOP total algo package.

I guess that makes sense now that gateway item 072 Eco Start-Stop Function menu is a stand alone choice/coding for brake HOLD and SBW and is not part of total ECO-Start-Stop package I killed.
So in non ECO-Start-Stop car all they got to do take brake HOLD power from main battery.

FYI, everytime ECO-START-STOP of brake HOLD item 072 and the True ECO-S-S item 76 get coded/re-adapted, the ESP system have to be reset or re-adapt too and to do it is simply erase the DTC and it would show a RESET bar progress ( on Autel ).

 

I wonder if auto high beams were not legal in your market, so they didn't code them in?

Also if eco start stop was still enabled, and you were at a stoplight with A/C and radio going, with car not running, wouldn't the auxiliary battery be running those accessories, at least until restart ?

 

No such regulation for auto high beam, our regulating body is like minus20 years too Jurassic Park.
If there is no gain in $$, they wont make any new rules. Some stupid old rules in fact still in force. Example is : run flat tire is not an excuse for a car to not have spare tire.
So new MB without spare tire cavity, get stupid stand alone spare tyre bag ... LOL.

Let say this small spare tire is 10kg, during a collision this spare tire can be a projectile. Good thing there is a back seat to protect passenger.



My cousin once had a Corolla GT/Trueno hatchback. The famous Initial D drift king Corolla AE86 ( in Asia ) of the mid 80s.


He installed an aftermarket JBL speakers and being a hatchback , the best place for bass ( non subwoofer ) is the small thin separator thingy at the boot, the small 2 speakers like below on the blue boot separator.



His collision was not at super fast speed max 60 MPH and not hitting a wall or anything, but his rear speakers, both...flew out of its mounting and one hit the front windshield and broke it.
He is lucky that he is not tall and his seat has high head support and protected the back of his head, otherwise I think he could get knocked out by the rear speaker the projectile.
The seat is below and it is the same as my MK2 Supra seat of the mid 80s.



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In theory, creature comfort equipment during ECO-STOP-MODE is indeed powered by the baby 12Ah battery at the trunk.
I believe even the HVAC blower may get AUX battery power since there will be traces of cold at the evap, maybe...I can't recall.

However I always disabled ECO ( manually using button at every engine start ) from day 1 I owned this W212.
I hate ECO-START-STOP, my Mazda mini van has this stupid shi-et ECO-S-S too. I told my driver to always kill ECO-S-S.
Good thing my Corolla Cross 2021 has no ECO-Shiet-Shiet

With Jakarta super duper traffic jam, only an idiot will operate ECO-S-S.
All bosses will slap silly his driver for operating ECO-S-S because cooling power will be reduced and cooling a car interior in our hot climate is number 1 priority.
More so lady bosses with thick make-up .... ha ha ha, their make up may meltdown.

 

This is using VEDIAMO software to disable ECO-S-S in elegant fashion