Dear all,
I have Mercedes W212, with 1.8L M271Petrol Engine. I have a red battery Symbol popping on the screen while driving and the symbol is intact despite several re-start. I tried scanning the code and it is showing an error code P065B09 : "The alternator has a Malfunction, there is a component failure". I have checked all the fuses and they look intact. Battery is brand new and showing 12.2V (even despite the alternator is not charging it and several re-start cycles). Alternator belt looks good and shaft seems to be rotating fine. While i was debugging the issue, I did notice alternator start to work momentarily with 14.2V reading and I could drive normally for 10minutes. However, when I switched off and restarted the engine again after 1hours, it was back to the same error. Any ideas if this would be a fault in the alternator control regulator or could this be the connection/communication between ECM and alternator or these are worn out carbon brush ? The car has done only 80K Km.
I would highly appreciate any advice or suggestion to further debug the root cause.
Thanks ...

Error code that I am getting

Good survey! Your M271 ALT failure is unusual.

The mileage being so low at 80k means it can not be "short brushes" yet.

Mercedes provide oil leak to soak in the alternator. Do a visual check of ALT.

Lets see what's bad the ECU side or the ALT side...

> QUICK TEST STEPS:
Next you can try to simply set ALT un self-control mode by disconnecting its plug.

What voltage does that setup provide?

If below 14V then ALT needs: cleaning, surgery or replacement.

Many Thanks for your suggestion! Just so that I understand your point correctly, If I disconnect the ALT - ECM cable, does it automatically go to self-control mode and start regulating independently? I have checked the ALT that my car is using (Valeo 439679) and it seems there is only a single connection from ECM that is routed to ALT (perhaps ground connection is taken from body?). I am also wondering & doubting if at all there is a good handshake between ECM and ALT. Unfortunately, the access to this cable is quite difficult from top and I have not yet started to dismantle stuff to remove the alternator. I will check if I can access this cable from the bottom of the car next weekend and update ... Meanwhile, Thanks again !!


Part Ref 439679

Give me your VIN, let me make sure.
If this engine is the very same M271.860 ( 1.8L Turbo , CGI ) as 2010 W204 C200, it is already using LIN bus single wire to alternator.
Removing LIN will make alternator own built-in controller does the charging and voltage management works, but it will only do so once RPM hits 1,000 RPM or more.
I removed the LIN from my friend's 2010 W204 C200 because his Green-Bull-shi-et-Save-The-World alternator charging management is WORSE than my E400 W212, which has ECO start stop, while his W204 does not.

I too removed my LIN M276.820 , 3.0 Turbo.

Thanks for your comments. Indeed, I have M271.860 Engine and alternator seems to be using LIN bus with a single wire. If you remove this connection, Alternator would become free running and perhaps might overcharge ? No ?

No, MB way of alternator charging management is not the same as other brands of car.
The alternator in use is a perfectly proper alternator with good proven charging controller.
The LIN connection to alternator is an over-ride command for ECM to tell alternator when to charge and when to not charge and also as a reporting facility when and if
alternator has a fault.

So without the LIN connected, the alternator goes back to its basic good self and charging does not go higher than 14.1 volts and amperage when battery is full, can be as elegant as 0.1 amp.

See the alternator elegant charging at 0.2 amps .........below : My LIN to alternator is disconnected.


.
Does your car get the dumb-azz radiator shutter too ? M271.8 is considered blue efficiency model. Not diesel blue thingy, but petrol.
I call it dumb-azz because in the tropics to put a radiator shutter is a suicide waiting to happen.

Here is 3+ years of test on the MB piece-of-shi-et alternator charging algo.
https://mbworld.org/forums/e-class-w...-charging.html



You can test your alternator own proper charger controller in action :
01. Turn on headlight and/or
02. Set HVAC blower to maximum speed.

The 2 conditions above is when the ECM does not intefere much with alternator charging profile, it will let alternator's built in charge controller to works its own magic.
You will see voltage not dipping to lower than 12.7V with the two above conditions, any one of the two.


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

Now, the DTC P065B09.
Tighten your alternator positive cable. Disconnect battery first please, both negative and positive disconnected is safer.
When disconnecting battery : Undo negative first and then positive.
When re-connecting battery, install positive first and then negative.

Check your F32 pre-fuse block , , there is a fuse for the alternator, see it the bolts are loose. You need F32 wiring diagram. I am attaching.
If you car is not an ECO Start Stop version, your F32 is a bit different than one with ECO Start Stop.

Usually when and if positive cable get disconnected from alternator, while engine is running, the charge controller ( voltage regulator ) of the alternator can get damaged.
There is so much power which can not be tranferred to battery you see.

Happy reading..........

Nope,
ALT-LIN disconnected ALT should SELF-REGULATE at 14.1V.
You want to confirm that voltage after unplugging ALT-LIN connection.

If the regulator brushes or diodes are bad you need to know and not simply assume ALT-LIN is 100% a magic-fix....
Can not help bad hardware.
Only help with unstable MB firmware

Many Thanks for your help and very useful sharing ...
I will go ahead and disconnect the LIN to see what happens ... This would be next weekend... Will keep you posted

as it turns out engine runs better on fixed 14.1Volts than standard swings 12.6V to 14.9V.

Make sure your batteries stay charged up, not drained.

Just to update and close the thread.... I could not really work on my car until only two weeks ago. Disconnecting the LIN did not help me recover the situation :-( Also I found lots of oil deposit on the alternator that was coming from and leaking turbo intercooler pipe Oring. Perhaps the oil leak had penetrated and consumed the alternator brush and/or regulator module. I put new Oring and replaced alternator with a used one in very good condition. Now everything back to normal !! Thanks to fellow colleagues for valuable suggestions and help ... Cheers !

Once oil leaks into the alternator, what is the best way to clean the alternator of the accumulated oil? Just spray it out really well with brake clean? Anything else to do?

Cleaning oily ALT it's a 50/50 lottery because the 3-phase rectifier diodes are pressed and instead of soldered.

The voltage regulator host the carbon brushset that must be clean to contact the copper rotor rings.

What have you got to loose, try and watch your chassis voltage while driving.

I think I caught this pretty early. I have no charging or battery problems, just some oil on the outside of my alternator. Need to get the brake cleaner on the alternator. THANKS for the info

Nice early catch!

The regulator brushes are reliable until 120kMi and become too short around 150/170kMi.