LILBENZ230

If the aux battery was dead, you'd get a warning in the cluster - Auxiliary Battery Malfunction.

You have a weak main battery. Replace it. H6 AGM.

Also please edit your post where you said this was the original battery that is 6 years old. Per your assigned reading, there is no possible way any W212 battery lasts that long. That is like.. 8 times longer than it should last since driving the cars actively discharges the battery. Obviously this is sarcasm and I'm sick of the other thread.. there's nothing wrong with the charging system of the W212 and 6 years of battery life is absolutely fine. The ONLY symptom my 2016 E350 had when the main battery started to fail was that eco start/stop ceased to function.

Good luck.

PS - Autozone testing is completely useless.

juanmor40

I am new to the Forum, though I have been reading it for a few years

Took me a while to read through the thread, and thank you all for all the insight into the charging system for the W212.

My problem starts with the "Auxiliary Battery Malfunction" message in the cluster ( a few months now)

1. Used ICarSoft OBD scanner --> No faults of any kind (but message Auxiliary Battery Malfunction in the cluster)
2. Check voltage while idling using the scanner --> @14.7 V (+/- 0.02V up/down)
3. Check voltage using the cluster --> @14.7 V
4. Check voltage (multimeter) at the auxiliary battery posts with the car OFF --> 12.74 V
5. Started the car, and recheck voltage at the auxiliary battery posts --> 12.74V
6. While idling checked the voltage at the "Accessory Power Relay" (A 000 982 2023) close to the auxiliary battery
   1. Input from main --> 14.7 V
   2. Output to aux battery --> 12.7 V most of the time, except that for a few seconds jumps (only once) to 14.7V and back to 12.7 V. Need to shut the car off to repeat the odd jump.

Any ideas?

Is the "Power Relay" attempting to charge the auxiliary battery and gives up for some reason or failure downstream? Say it detects the auxiliary battery is no good (incorrect resistance or else), or the relay itself is damaged?

I have charged the auxiliary battery (out of the car) in the past, and the message goes away for a few days (the Eco/Start/Stop comes back with fury) and after a few days, the message is back and the echo/hold functions stop working

If a Genuine MB battery providing consistent 12.7V day and day out is a bad battery, I am not sure what kind of battery my W212 wants.

Thank you in advance
JC

Bhopkins

I would suspect it is time to replace the auxiliary battery. From my personal experience, and from watching the experiences of others here on the W212 discussions, 6-7 years seems to be it for the auxiliary battery. Do some searching and you will see a lot of postings in the last few months by those of us driving '14 model year cars.

Replacing the auxiliary battery on my E350 Sport made the Auxiliary Battery Malfunction message immediately go away. And the brake hold feature immediately started working again.

juanmor40

Thank you for the prompt reply. I have been following the different threads about the aux battery for a few years. It just happens this time I would like to know what is the source of the problem, and not throw another good battery to be eaten by a real hidden problem.

Perhaps my fault, I should have also stated the age of the components:
- The car has @71K miles
- The main battery is @2 years old (2nd battery since I own the car), ballpark 25K miles
- The auxiliary battery is @2+years old (3rd aux battery since I own the car), say 30K miles, but the message started about 5K miles ago.

From the above, I would say the 1st main battery lasted @5 years, but it never hinted at a failure. I just changed because the service said it did not pass "the test" during a service + 5 years and possibly I fell for it prematurely.

What has puzzled me since the first aux battery passed (under warranty) @20K is that the 2nd battery passed @40K+ (which was also replaced under warranty), and the third one (no longer under warranty) is bugging me since the 66K mark.

Do these batteries last only 25K? It is becoming like a longer interval oil change. Basically 3 aux battery between one oil transmission service.

If there is no choice, I would have to pony up the new one, and wait for its failure in @20k+ miles.

All the best,
JC

S-Prihadi

To know how charging is done for AUX battery, read here : https://mbworld.org/forums/e-class-w...ml#post8337068

CaliBenzDriver

Your car detected a tired AUX Battery that it interpreted as a spent battery (abnormal internal resistance).
There is a TSB SW Update about that very misinterpretation, at least applicable to MY'14-M276.
​​
PASS OR FAIL:
Mgt software tries to assess the AUX battery internal resistance by mesuring its voltage alone under a standard load...AUX has no battery sensor or current probe.
-> AUX being under charged is misleading and causes SW to safely disable BrakesHold etc... That is a real condition.


QUICK STEPs:
Put a reset on both SAM's to make them forget the low AUX voltage condition they captured.

Charge your AUX then evaluate if your particular car has an abnormal charge problem.

juanmor40

Thank you, Cali. It seems I did not check the SAM_F/R correctly (newbie with the iCarSoft), found the following

• B1E211B: The buffer battery has a malfunction. The limit value for current has been exceeded
• B11C116: The additional battery has a malfunction. The limit value for electrical voltage has not been attained

So I proceeded as suggested

1. Deleted both codes
2. Charged the aux battery, the standalone voltage jumped from 12.4 V -> 13.5V
3. Let it sit for an hour, and connected back.
4. Started the vehicle, and waited 5 min, no messages nor fault codes so far. So fingers crossed.

I will drive out later, and update its status.

Once again, thank you all.

CaliBenzDriver

Give yourself a big hand for your quick learning. Reality was not misterious.

I believe ​​​​​​your car is going to be satisfied with AUX until the same conditions get reproduced in give or take 2 to 4 weeks period... hopefully longer!
👍

juanmor40

Update:
Started the car once again, and unfortunately the message "Auxiliary Battery Malfunction" came back.

Got into the IC Vehicle Data menu, and monitored the voltage/current during a 45min ride. I wish I have the car instrumented as S-Prihadi has it, but I think a "yo-yo" is an understatement of how the charging system behaves. There are several charging periods with different voltage and current used, but I do not understand how on Earth I can be standing on a red light at 12.2V and current -20A, yes -20A (+sometimes). Once the car is going, randomly changes back to 14.8V (max I recall 14.9V). The longer I drove it, the more often the car showed 13.0V and between 2A-3A charging with the occasional 14.8V and surges of current up to 50A, then slowly down to 20A, 12A, and gradually back towards 3A range.

On Sunday, I thought my alternator regulator was on his way out and justified to myself the wild rides. However, after experiencing the start/stop/hold functions working again for a few minutes I am certain the batteries have to be good; otherwise, the "not good enough electrical resistance" theory does not hold water.
I had both batteries for hours on CTEK until step 7, and no problems. Noticed the charger does not spend too much time from 1->4 on neither of them.

Yesterday, took it for a 65mile ride (@1:15min), mostly highway, and when stopping and going at the destination suddenly the start/stop ECO started working. Even the brake HOLD feature worked as well. Returned home (after another 65 miles), and back to the Malfunction message.

From my coarse monitoring of the IC, and the wild excursions in voltages and currents
1 - There is no battery that can take such an abuse and last 5-7 years. Surprised even last 2 years.
2 - Either someone on the MB engineering team was smoking something else, or there is a subtle software defect that gets triggered and recovers itself over the long run or when the car is turned off, and back again in the next trip
3 - There is some kind of ground fault or loose connection in the car. I checked the basics: battery posts, and ground posts on the body and they seem tight.

At some point, any good battery subject to this abuse will start showing some kind of "electrical resistance not good enough for MB control system" even if fully charged. After yesterday's ride, I measured the voltage on both batteries: main 12.7V and aux 12.8V but the message was there.

Definitely confused, and I will pass buying new batteries (@$320 for main + @$150 for aux) just to remove the message. Wait a bit longer for ideas to figure this out as long as the batteries hold a charge.


Separately, noticed the AC fan running for quite a while (25+min) once the car is off. I left the garage and nothing was running, and when I came back to check on the CTEK I could hear a humming sound behind the main battery. The AC is so smart, it tries to dry the evaporator even after the car is OFF to prevent foul smells. I guess it runs until it is dry, or drained the battery enough the smart charging turns everything OFF to prevent further drains.

bmwpowere36m3

Read this: https://mbworld.org/forums/e-class-w...n-battery.html

Some of the behaviour you see is "normal"... I don't know if S-Prihadi got down to the bottom of his fluctuations and more importantly the low voltages he was seeing (below 12.6 VDC). Though he has recent a thread about cleaning the ground points... My experience on our non-start/stop W212s is fluctuations in charging occur, but the main battery voltage doesn't dip below 12.6 VDC while the engine is running.

That said, aux battery replacements are fairly common and they don't last too long, search around. Even the main batteries giving the SOC and charging profile that MB has gone with to gain a smidgen of MPG.

CaliBenzDriver

it seems you are getting a pretty good pulse on how your car charges its batteries and supplies voltage to consumers.

Anytime your voltage with engine running deeps below 12.6V (12.5 momentarily) is a cause for concern about abnormal battery discharge. Nothing that I know of in the multi-stage alternator control involves deep discharge, only charge or float.

Both battery are wired to supply voltage through a one-way diode (in their respective MOSFET 'solid state relay") when the alternator does not supply voltage. During the ECO restart phase, the PreFuse extension of the F-SAM can disconnect the MAIN battery by opening its MOSFET SSR to use all its energy solely to restart the engine. The AUX then momentarily supplies active consumers while the MAIN is out the circuit minus to feed the Starter motor.

The supply voltage going below 12.6v is what ends up draining AUX when it should just seat there, doing nothing with its diode blocked by a voltage a tad below ALT and MAIN. When everything else fails AUX automatically chips in through its diode while both SAM manage onboard consumption.


The alternator putting out voltage between 14.9 and 12.6v does not mean its LIN controler is fully functional. It has multiple ways to fail.

juanmor40

Update:
After reading the threads about checking and cleaning the ground points, I started with the trunk

1. Cleaned the ground connector to the body
   • A bit of oxidation and some whitish stuff, probably some kind of dry compound as mentioned by Cali elsewhere.
2. Cleaned the two AUX battery (square) posts on the top where the cable connectors are attached to.
   • Cleaned the connectors as well.
3. Cleaned the connector on the other end of the positive cable where it is attached to the relay
4. Cleaned the contacts on the inline fuse next to the relay as well

I added a bit of the battery corrosion protector compound I got from AutoZone (I know I know). Cleared the only code in the ECU: "The buffer battery has a malfunction. The limit value for current has been exceeded"
Started the car, and waited for the message. Like clockwork, the message was back again so I decided to let it go for the day.

Had the car for a long ride the day after, and from nowhere the ECO light became green again. Engine stopped at the traffic light, light back to yellow, after 1/2 mile became green again and the cycle repeated for the whole trip. Perhaps it was my "Father's day present". Monday the car behaved similarly, so two days working

Since the light was going from green to yellow in a single engine stop, I decided to clean the ground post under the hood and charge both batteries with the CTEK overnight for the AUX, and morning to afternoon for the main. The AUX was at 12.8V after the charge, but the main ended just at 12.45V (perhaps it is not in good health?). Took the car for a ride, and surprise: The yoyo charging algorithm started from the get-go, with long discharge periods of -20A @12.6V on the cluster diagnostics. The yoyo thing was like that for the whole ride, and back. No words to describe the frustration.

Today I had the car out again @20min, and no yoyo behavior, and the ECO light changing between green/yellow between stops and go's.

So far, the cleaning of the ground points and a few connections in the trunk seems to have changed something. Tough, I am a bit worried there could also be something loose in the back as well and after moving things around something could now be in the "right position" to work.

I will continue monitoring it before jumping for new batteries (perhaps the main is showing signs).

Thank you all for the great information posted on other threads related to this electrical issue.. Very educational.

S-Prihadi

When measuring the Main Battery after it is fully charged :
Lock all doors and kept hood being open, but wait 2+ hours after any doors being opened or any activity inside the car and DO NOT use Instrument Cluster Voltmeter function, use stand alone DMM at battery post.
Keep FOB key far away.

12.45V is because the computers have not sleep well yet and is doing its drain. Hence the 2 hours wait in necessary.

Try and let me know , you will see 12.7ish volt by then.

ADD :
The yoyo charging is what I hate too, but that is part of the ECO algo. There is nothing we can do...sadly.
I also think that, our B03 Eco version with baby 12Ah battery at the trunk is way more abused ( YoYo-ded ) by the algo more than those with voltage dip capacitor instead of baby 12AH battery.
MB probably thinks, heck that is why we place a 12Ah baby battery at the trunk for..... ha ha ha ha.

juanmor40

Update:
Instead of waiting, I decided to disconnect the battery and directly measure the battery standalone, and you were right --> 12.8x V which is also close to the measurement on the AUX after charging.

Connected back again, and measured on the posts (12.45V) and the cluster (12.4V).

Summary: I have two batteries (main and AUX) that are up to specs in voltage, but do not consistently pass the test to get a green ECO display in the cluster.

NOTE: I have never had a problem where the car had issues starting. So, it is more a nuisance with the message being displayed.

DeutscheBenz726

Everything on my 2016 E350 worked EXCEPT the ECO/stop/start.

I finally broke down and got a main battery from Auto Zone (the best one that they had) and took it to my mechanic to put it in (none of the automobile parts people would touch it!) and now the ECO stop start works with a vengeance!

Be careful what you wish for though. Now that mines working the startup is so jolting that I turn it off most of the time!

bmwpowere36m3

No load, battery voltage isn't an end-all test...

Charge both batteries with appropriate charger, clear codes, disconnect main for 10 minutes, reconnect and go for drive. If you get the aux batt message... well its time to replace it or live with it. ECO not functioning is almost always resolved with new batteries or charging them if the car isn't driven around much.

Choose your adventure...

juanmor40

Thank you.. I understand that voltage alone does not determine the status of health of a battery; however, replacing it without a clear understanding of the source of the problem is just postponing the issue, i.e. a paliative. As mentioned earlier in the thread, it is the 3rd AUX battery, i.e. I will not be fixing anything but the message by replacing the battery again.

As long as the car continues to start well, I will take the adventure of ignoring the message and trying to figure it out if possible.

CaliBenzDriver

This topic may seem a little disjointed with two distinct POV....

ALL cars clearly do require batteries replacement at some point based on couple factors (high heat locale, sulfation, discharge history, age, etc...).

Most cars have a well working charging system with or without ECO, no problem.

BUT... some sick cars eat batteries by discharging them below 12.6v while driving. Not all of them do that!

I can see how someone with a normally charging car does not understand why anyone would care to pin down this problem... just like warped rotors are not my main concern.

Replacing battery is great if your car needs one but it is not a simple cure all.
If your car goes into deep discharge after its quick charge cycle (14.9 +12.6v) then a new battery is only a bandaid on a wooden leg.


Discharge level is about voltage not current:
When the cluster shows voltage swinging from 14.9 to 12.6 with -10 Amps, it's actually not discharge... only surface-charge coming off.

Discharge is anything significantly below 12.6v for a prolonged period. 12.3... 12.1... 11.9... 11.7... new battery won't fix that problem - On top of that you pile 80Amp charge currents and you get SHORT LIVED BATTERIES. That's when you realize something is seriously out of wack. 🤣

When dealing with a low battery, the question is:
Is your Benz draining its batteries while driving?
If No >>> BUY a replacement battery.
If Yes >>> FIX charging system.

This topic is of interest for owners plagued by low voltage swings otherwise it's irrelevant.
✌️

LILBENZ230

Glad to see you got this sorted. The start/stop function not working was the first indication for my car that the main battery was bad. The AUX battery was original and functioning correctly when I sold the car.

bmwpowere36m3

If I had a '12+ I'd measure it myself... but besides S-Prihadi, I don't believe we've seen the charging profile in action for later MY w/ ECO. I'm all for finding the root of the problem...