Hello everyone,I’m hoping you can help a fellow enthusiast . I’m currently having an issue with my charging system that I can’t figure out,I was hoping someone can give me some insight. A couple of months ago, I received a battery warning while driving home. I quickly got home and checked my voltage with my multi meter. It was reading 11.6 volts. Suspecting the alternator I shut the car off. But I didn’t have time to diagnose it so, I just put the battery on a trickle charger for two days to see if I could recoup the battery. I got the battery to 12.2v (not ideal but not terrible) when I started the car, too my surprise it was charging to 13.8v. I drove the car around and noticed that the volts and amperage fluctuate Wildly, 12.1 - 13.7 volts while driving. Amps from -50 to +60 Eventually it would go to 11.7 again and trigger the light. To be on the safe side and not mess with the regulator, I just replaced the alternator with a new one. But, I’m still getting the same results on my multi meter. Also if I drive for more than 30 minutes my battery light still comes on. Soo, is it my battery. Or something els? I checked my belt it’s nice and tight. The battery sensor I unplugged and cleaned, I also checked grounds everything looks good. Any insight would be greatly appreciated!

 

Welcome home, you have lended in the right place to enhance your MB ownership. We can help you cancel chaos from the money pit setup. These are great cars once a few genuine issues have been eliminated.

You have E350 MY'11 with an issue of discharge while driving. Mercedes calls this "opportunistic charging". We affectionately calls this game "YOYO VOLTAGE".


The long story shortcut is you may decide to join a few experimental owners by:

1. Unplugging Alternator Control
2. (Unplugging Oil Pump Control)

Both of these controls contribute to unnecessary troubles with marginal power and lubrication.
It may sound counterintuitive at first to disable controls but it turns out when abused these controls create costly issues.


There is no better quick-fix I know that can get these systems sorted out faster. The root cause are handcrafted issues that Mercedes may or may not have eliminated with design change updates.

In addition to faulty logic conditions, the voltage YOYO swinging below 11V directly originates from subpar networking performance between the two SAM Modules.


-- The smart charging between 12.6V and 14.9V is what happens while this system works well.

-- When it disfunctions the ECU causes the alternator to short out the battery after driving a while.

-- This results in destructive 90Amp swings that overheat alternator and both batteries.

-- Its a brilliant design implemented poorly with very few fault checks.

The outcome is both bateries get drained by driving and cars eat tough AGM like candies


Connecting a float charger on batteries and displaying live voltage while driving are great counter measures.

Repair work may involve cleaning painted GND Posts, dealing with solderless chaos makers - These solutions positively solved my voltage YOYO swings but I still do not get a normal 12.6V float control by R-SAM.
I am working on testing a solution for that multilayered issue.... ✌️


> SHORTCUT TIPS... not foolproof:
-- CONSIDERING the amount of rework involved, pulling the ALT LIN Control maybe the best solution for most savy owners.

-- Do proceed under your own supervision by monitoring ALT with IC Display. Advanced stuff may not be foolproof.

-- As noted, replacing new ALT + MAIN + AUX do nothing to cancel YOYO business.

-- Good working solutions are limited: I don't think any top notch factory trained MB dealer can fix that !!!


++++ AMP CURRENT ++++
Good job on keeping an eye on AMPS
Amperage helps measure how deeply discharged the main battery is.

• HIGH values are bad news greater than 30A
• NORMAL values are like 15A and less.

++++ ROAD CRISIS PROCEDURE ++++
Crisis mode usually takes place when ECU tries to enter the "maintenance float cycle" while driving. Instead of 12.6 it practically aims much lower like 10.6V

When you spot Crazy YOYO Volt/Amps:

1. Find a safe place to park
2. stop the engine
3. lock the car to sleep
4. Wait 10mn patiently!
5. Resume driving, ALL is good for a while.

This procedure limits abuse done to the car components.


++++ YOYO 2 4 1 killer : (MAIN + AUX) ++++
As soon as the ECU swings the ALT voltage below 12.5V then AUX begins safely supplying its VIP Modules (ESP + EIS + ?) with backup power - This is done reliably through diodes.

The outcome is while MAIN is being drained, AUX as well but at different rate.
AUX is drained only by the load of its modules
MAIN is drained by ALT shorting it through lowest resistance path. Weak Chassis-Engine strap limits this current with its resistance.


The bad news is AUX is small capacity makes it sensitive to its charge current being unregulated...
When 14.9V returns, it fries AUX with high current.

A little back and forth yoyo equals a spent AUX with high "internal resistance" calculated by R-SAM.

 

YoYo charging..............

 

Mine was doing that, often hovering in the low 12V range and sometimes dropping to low 11's. Once it gets in the 11's it doesn't want to recover.
I can turn the eng Off and right back On and it resets it. No need to wait fyi. It sucks because keyless go won't let me kill it/restart while moving, I have to stop the car... I spend most of my time on the freeway, and even if not there is rarely a place to pull over, so this sux. I tried pulling the start button and inserting the key, but it won't do anything at all. It has to be started with the key to work. I hate the key more than the problem so I'm not doing that.
If turn the heater or AC on full blast, the voltage jumps to >14, so that's what I do. Not one click from full blast, which does nothing, but full blast. I can only assume it triggers some override command that bypasses the problem?

The ECU is supposed to control the alternator on my car. I have a spare ECU and it changes nothing, so I guess something else is triggering this. Like Cali said, something like the CAN bus is probably causing it to go into this bs mode. I know I have a CAN bus issue, but good luck figuring it out. Not only is that complicated to narrow down, but apparently it only happens briefly ~ once an hour or so, which is about how often it drops <12V. So I suppose you could monitor CAN bus codes and see if they jive with the voltage drop.

Later I tried unplugging the little box thingie on the negative batt cable terminal at the batt. I forget what it's called, but the point is the voltage then measured around 13.8 and barely moves, no matter what. Seems awesome right? The problem is that isn't enough. When I turn the eng off and check the battery with a multimeter, it's 12.4, sometimes a bit less.

So, after getting tired of that, I plugged that little neg batt terminal box thingie back in a week ago and so far it's better than it was. Still not good, just better. Now it hovers ~14.2 most of the time, and when it does drop it goes to ~12.4. So far it hasn't dropped below 12.2 except when I floor it. That's another issue, voltage drops .5 or more when floored, which for some bizarre reason is normal. The problem is if I'm low to begin with, like 12.2, then it drops to 11.7 or less. This can cost boost pressure and limit fuel delivery, maybe even spark strength, so it's completely unsat. Why drop voltage when you need it most? Apparently the theory is it's reducing the alternator load to give you power, but in reality I lose substantially more than any potential gains. If someone at MB has an IQ above 100, I'd like to ask them a variety of questions.

So, assuming yours is setup like mine, I would try the heater/AC fan thing. If that fails I suppose unplug that box thingie on the neg cable. Someone suggested unplugging the plug on the alternator, but I don't see how my alt could work at all like that. From the looks of mine, those wires power the rotor. The theory was the wires are for a signal command to tell it to cur or reduce power, so no wires means it operates normally all the time. Maybe that's true on a different model? Or maybe I'm wrong, but someone would need to explain it to me. So if you can reach that plug on the alt, I suppose pull it and see what happens?

Fyi my aux battery is the oem unit, mfg early 2015. Not sure how 14.9V would hurt it, but I've had this issue for a long time and the aux batt is still fine, somehow.

 

Valeo regulator is independently smart enough to auto-regulate its output. It has an internal shunt to measure current and definitely voltage as well. Without LIN Control it works in default mode... far better than what ECU can do.
​​​​​​
The Hyundai thingy on the battery neg pole is also a smart LIN device.
It's a battery manager that measures these vitals:

1. internal batt temperature,
2. voltage
3. current in/out

It has an ultra-low snoozing current in microAmps because it is always powered ready to measure battery charge.
It's a licensed version of proven Bosch battery sensor into Korean maker.

This unit also packs some independent smart on-board firmware to tally battery health status - Its not total cheap dumbo sensor.

Headlights ON trigger minimum guaranteed safe voltage just like MAX HVAC but with less load.

Best bet for now is ALT LIN OUT ✌️


+++ Acceleration drop... 13.7v
during acceleration, EVU stop s charging the battery. It it was providing 14.4V is temporarily backs down to 13.7V before resuming a higher charge voltage.


+++ Float only... 12.6V
When the battery manager is satisfied with battery status it calls for the maintenance voltage of 12.6V. Alternator then keeps supplying 100% of the car load under 12.6V only.


+++ Crazy control.... bad part time only ! 👏
Because the GND Reference are all jacked up no where near zero due to carefully painted posts, voltage measurements are skewed (actually screwed!).

CAN-Bus networking between the HELLA R-SAM to BOSCH F-SAM is glitchy enough to miss the Bosch ECU mark that drives the ALT logic in the weeds.
✌️

 

Thank you everyone for your help a lot of great suggestions! I will look in to more ground locations anyone know where I can find a ground location diagram? I did try unplugging the battery sensor on the negative post, the car sat at 12.8 v and didn’t move. I have not tried unplugging the regulator yet I’ll try that next. I really love this car hopefully I can figure out why I have the yoyo voltage and I will report back.

 

Here u go : https://mbworld.org/forums/e-class-w...-database.html

Here is the special W-FT ground, which MB never even list it in the WIS.
https://mbworld.org/forums/e-class-w...ital-wire.html

Happy cleaning................

 

Lot's of great guys on here, remember though, your 2011 has no extra battery, it has a small battery behind the left side dash panel for transmission shifting in case the main battery goes dead. Also very year of "smart charging" was different, they updated this system every year so what's programmed into a 2016 you don't have, there are many similarities though, car still only charges the battery to 80%, leaving room to charge when coasting or braking.

 

Thank you everyone for your suggestions is was extremely helpful. I was able to fix the issue so hopefully this will help someone els that has the same issues as me. I went about removing all of the ground locations and cleaning all that I could reach. Finally I made it to the underside of the car where there is a ground point on the transmission to chassis on the driver side. It was completely corroded over, I just cleaned the ground point and the car runs extremely happy now! I’m getting 14.6v max and 12.7 when fully warmed at idle so seems to be fixed. Again thank you to everyone for your suggestions and guides I was truly flying blind.