It would help to fill out your profile so we know the year and exact model.

With the W211s (and most modern cars) your issue is clearly a failing battery or
something in the charging system. My bet would be battery. Have the front and rear
batteries tested. If in the US call roadside assistance. They will isolate the bad battery
and replace at no labor cost and usually a better than retail parts price. If you have
a load tester and a multi meter you can test both batteries and replace the offending
battery. If it is not a battery then most likely the alternator has started a nosedive and
will need prompt replacement. For that I recommend getting a Bosch OE replacement
and having a reputable German/MB after market shop replace it. An MB dealer will tear
your eyes out on the price of an alternator install and battery replacement.
But just go one step at a time. If the batteries test healthy then all connections and
ground wires should first be checked for tightness and corrosion.
If the wiring all looks good the load test can tell if it is the alternator and at that point
you can have the repair done.

 

^Correct and the consumers switched off means the computer has detected a low voltage situation, normally this happens when the rear battery is going bad. This way the voltage remaining allows you to drive the car as far as a workshop. But I would go with Noodles suggestion and call roadside assistance.

 

I recently had a similar problem after already having both batteries replaced. My wife was out of town and had no choice but to take it into an MB dealer. First they thought it was the battery control module, then the alternator but ultimately it turned out to be the wiring harness.

 

Hi I think I’m having the same issue. Can you tell me what wiring harness?

 

its a 2003 E320
and i have tested the battery after the car hasn't been started for about 3 hours on 10 degree weather and battery showed 12.6 volts, alternator showed 14 volts and the little battery under the hood showed 11.6 volts and it shows a lil corrosion on the cable on it so my guess is it might be the little battery under the hood? i dont know what else to look into !!!!
and thank you guys for all the help i appreciat it

 

11.6V, The battery is kaput

 

what do u mean ?

 

I mean anything less than 12v and the battery is no good.

 

so u think i should get a new one? where do i get the battery except the mb dealer ? is there anywhere else they sell em ? if not r u aware of how much is it at the mb dealer ?
thanks

 

so u think i should get a new one? where do i get the battery except the mb dealer ? is there anywhere else they sell em ? if not r u aware of how much is it at the mb dealer ?
thanks

 

100% it needs a new battery but I cannot help on where to buy as I am not in the US, but this may help:

Recommended Repair Shops - Benzworld.org - Mercedes-Benz Discussion Forum

Mercedes Parts, Mercedes-Benz Parts

 

They are over $200 at the dealer.

Roadside to the rescue or you can save about $120 and get good sealed AGM from
Batteries Plus, Advance, Autozone or even Walmart. Make sure the orientation of the
mounting posts' polarity is the same. I got mine at Advance for $80. The polarity was
correct and the MB OEM bolts that screw into the cable were even the proper size
and thread pitch. Ten minutes with a 10mm deep well socket and I was down the road
problem solved.
Advance Auto Parts: 12-Volt Sealed AGM Premium Batteries for Powersports Applications by MagnaPower - Part ETX14