it_is_nerdy

Got the Battery/Alternator Stop Vehicle warning on my way home Wednesday and by the time I got it home there was very little battery. It wouldn't start again after parking it.
Ordered the voltage regulator from AutohausAZ and had it Friday morning and installed it this evening. It started but the errors were not going away. Swapped batteries with my other Mercedes wagon and drove it around the block a few times. At the end since the warning was not going away I called up the voltage in the gauge cluster and saw that it was gradually decreasing and never was above 12v.

What are other causes for not charging?

Thanks in advance, this will be my weekend until it is fixed

rapidoxidation

There's a battery control module (BCM) in the trunk that
wait for it
controls the batteries. It'd be worth getting a proper diagnosis prior to throwing that spendy part at they car though.

it_is_nerdy

Hi Rapidoxidation, cool username!

Do you know how to test the BCM? I have DAS and am pretty comfortable with it; but the W211 is new to me. Thanks for your quick post!

konigstiger

See attachments.

it_is_nerdy

Thank you very much konigstiger! Going to the garage now to test now! Will report back.

it_is_nerdy

Back from the garage and somewhat relieved; the BCM seems good and passed tests in DAS. I tested the relay as well and it seems to be working as well. This lead me back to testing the alternator - I get -60ish amps on initial start and it never goes into positive values and the voltage continues to drop at the main battery. Either I got a bad voltage regulator, there is something else wrong with the alternator - or there may be a wiring issue. I will pull off the panels under the engine now to visually inspect. Thanks again for the great documents.

it_is_nerdy

Reading current to and from main battery, the BCM is reading this which tells me that it is ok:

This is with the engine running (discharging at 44.5 amps) :

Interior CAN check shows it communicating with the BCM also:

Unfortunately another system seems to have a connectivity issue with the coolant and washer fluid reservoirs:


Tomorrow I will try to check the voltage at the alternator and plan to remove it to take to an alternator shop to rebuild if it is not outputting appropriate voltage.

Thank you again for that ( WIS? ) document, that was extremely helpful.

it_is_nerdy

[deleted duplicate]

it_is_nerdy

Today pulled the alternator which was a bit difficult to do because I had to remove the fan shroud and broke the end of the coolant bypass line between the reservoir and the top coolant lines. Hopefully the dealership has that item available.
The alternator was tested as only producing 11.4 volts at pep boys, which is likely the reason for our problems!
I will find an alternator shop to rebuild it hopefully tomorrow - does anyone have a referral in Orange County, CA?

Thanks again for the help so far!

it_is_nerdy

Replacing the alternator was required - now it is charging correctly! Thanks again for the big help konigstiger!

edtse88

I was having a similar problem. I'm wondering if you cleaned off the contacts around the regulator and alternator when you replaced the VR. I think that was my issue after replacing the VR. I'm still testing my car since I recharged the aux battery and cleaned the alternator at the same time. But so far, I haven't had any issues with convenience function/red battery indicator.

it_is_nerdy

Hi Edtse,

Looking back, I wish that I did that in a more serious way - I only scraped at the bit of oxidation I found there since it was pretty thin; but in retrospect, I should have given it a good scrub with a wire brush. They did test it at Pep-Boys though and I *imagine* they got a good contact with it with their leads.. but who knows for sure.

Thanks for the input, I will keep that in mind when the next alternator issue comes up. With the W202 at well over 250,000 miles and the W210 over 210,000 miles, this will likely come up again, so I appreciate your input!

Have a nice weekend.