w211 charging problems

[phatlad]

hi all i'm hoping someone will be able to help. I've got a w211(s211) estate. a few weeks ago it came up with a battery/alternator warning, checked the batteries and charged them both up then checked them with the car running and they were only showing 12.5v. so I changed the alternator and after that, it was working fine. sadly now I have the battery protection warning. checked the battery voltage at the battery and on the dash, it kept changing between 12.6- 13.5v. i put the multimeter on the alternator directly and that was showing a steady 14v. Could this be a sign the BCM is dead? or is there something else I could have missed?

thanks glen

 

[mersum1es]

Or wrong voltage regulator. When regulator is not communicating with ecu, it goes 'limp' and charges constant ~ 14,3V. Or then you have grounding problem, corroded BCM wires or, like you said bad BCM.