Noureddinee

Hey , i have changed the battery of my w212 yesterday because the one it had was a cheap one and dies many times the previous owner had this battery ,the new is compatible for the car and the battery is test and running well , i drove the whole day with the new battery no issues , today i went to work in the morning, when coming back ( I was accelerating sometimes ) the red battery light came on , the car still functions very well and all electrical stuff is working

i took it to the diagnostic we checked the voltage , when the car is not running the voltage is 12.4 when the car is running 14.2 ,but we didn’t test it when accelerating so maybe the voltage goes above 14.7 when accelerating?, anyways we checked if there’s any codes and there’s none , after 2h the light came on again after i accelerated multiple times

the red light goes off when i turn off the car once i drive and accelerate the light appears again

where can the problem be sorry for my bad English, any suggestions or advice with this problem will be much appreciated.

KEY08

Sounds like an alternator fault or problem with the intelligent charging system. It shouldn’t be your new battery.

Noureddinee

what is the intelligent charging system

rapidoxidation

What are you using to check for codes?
I bet there's codes...

lucidbenz

Probs Alternator
I will tell you that it'll bust and you'll be left on the side of the road. Happened to me on Sunday!
Light came on, on Thursday. Had to call towing at 2am.
Now I'm looking for alternators, anyone have any input on getting it rebuilt? as oppose to buying a brand new one?

Noureddinee

the diagnostic device

CaliBenzDriver

You have just replaced another main battery and the car still displays low charge warning.
Alternator was shown capable of 14.2V... not bad.


There are couple quick solutions to help you with this issue.

-> Simply drive with Headlights:ON !
this will bypass sick ECU control to supply 13.5V or better.

-> Disconnect LIN ALT control:
this will let alternator regulator self-control its voltage to supply 14.4V flat. A new alternator/regulator won't provide any relief.

-> Find what crashes the ECU ALT control:
Your finding that engine accelerations cause this issue is a very keen observation. In many cases this problem can trigger lip-modes for WOT fans.

-> Useful on the way home late:
Cycling the ignition key resets the ECU for temporarily relief...

Try to measure you car voltage and keep it at 12.6V or above for safety. Book an appointment with a qualified MB specialist.

Noureddinee

thanks for the informations. I got it checked today and we found that the battery is not charging so there’s a problem in the alternator, tomorrow they will open it and check what is the issue there

KEY08

The battery light on your display is always indicating a problem with the charging circuit. You will never get a battery warning, with the exception of an auxiliary battery warning or a key fob battery replacement warning, which are graphic warnings and not an indicator light. Hopefully they will get it sorted out quickly.

ChrisHimself

You won't actually ever see a red battery icon for the battery itself, it just means the battery is not charging. I see this issue every day, and it gets misdiagnosed as a battery a lot, although you should usually replace your starter, alternator, and battery at the same time since they all wear each other down from not being in good shape. A depleted battery that won't hold a full charge ends up overworking the alternator, and the starter ends up pulling more current than it typically should and roasts itself.

Change the alternator. You can use Yourmechanic to book a mechanic to come fix it for you at your house. I recommend going to AutohausAZ and ordering their Bosch reman for your car and using Yourmechanic for labor only.

Noureddinee

Update : so i got it checked and it was the alternator voltage regulator thankfully i didn’t have to change the whole alternator now the battery and the car running perfectly, thanks for all the answers guys

CaliBenzDriver

New regulator brushset cured the deep voltage swings during accelerations - Great👍

What's your current odometer mileage like, around 100kMi??

Noureddinee

you mean how many km the car is on now ? 169k km

CaliBenzDriver

Yes, 170KMeter is on schedule with a 100KMiles design life.
Good maintenance item: ✅
​​​​​

CaliWils

I’m glad you have a decent and trustworthy MB mechanic. Some, if not most, will just say replace everything even though it’s not the issue. Thanks for sharing.

Left Coast Geek

the alternator is controlled via a LIN bus (low speed 2-way serial data communications on 2 wires), and the battery is monitored via a smart 'shunt' on the ground terminal, both of these are connected to the ECM, the ECM monitors the battery state, and tells the alternator how much to charge it, goal is to minimize the engine load from the alternator when it can to improve power/efficiency.

orb

I have a 2007 w211 that is having a similar issue. The 07-09 do not have 2 batteries, like the earlier w211's.
Water got into my from SAM from a car wash and shorted it out. Starter engaged and stayed engaged until starter burned up and then SAM continued to smolder.
Had SAM replaced and starter replaced. Cranks and runs fine, except Battery light symbol comes on after about 10 seconds at start up, and then ac compressor kicks off.
I replaced alternator, thinking the overload/short had fried the regulator.
Battery light still comes on, ac still kicks off.
Pulled up voltage on dash display, 12.3 at start, climbs to 14.2 , then battery light comes on.
I swapped batteries, nothing changes, not a bad battery.
If I pull the plug on the battery sensor, on the negative terminal, nothing changes.
When the SAM shorted out and the starter stayed engaged, the battery terminal and cables got very hot.
Could this have fried the battery sensor?

CaliBenzDriver

the only way we're going to know without replacing too many good parts.... is by using a good compatible scanner.

Under 10mn you will know if the battery sensor survived the fatal starter event.

W211 has a BCM module that's involved with battery issues.
🤞

orb

I replaced the Battery sensor, did not fix the issue. Gotta get another star multiplexer to scan car.