clvincent

need help- 2006 e320 with 339,000 miles on it, 90% sure it had the original alternator
BCM and relay replaced i think 7 years/140,000 miles ago

got the red light and used icarsoft to show 9055

took it to a good mercedes independent in tucson and they diagnosed bad alternator
replaced that and the belt -supposedly it drove fine for 10 miles then the light came back on
they ran star and say it needs a new bcm

new codes now 2248-4 and 2249-4 check G2 generator- these were not here before the alternator was replaced

i pulled the BCM to check for corrosion and it is pristine on the plug and inside the BCM

this car has a base model edge monitor plugged into obd port reading a few parameters one of which is real time voltage so i can watch everything, i know exactly when it is charging and not

not sure what to think

i picked the car up from the shop because i can do a BCM myself and it would just be sitting there until tuesday

Initially was running 13.9-14 on the edge monitor, in 3 miles it dropped to 12.4 like something is clicking off
took it back and they said bad bcm again, i am guessing they are scanning it with the star machine
what i dont understand is i thought bcm did not control main battery charging only aux battery

so i have driven the car around some the last couple of days in town and on the hwy trying to watch what it is actually doing

sometimes it is fine

if the charging voltage drops off 50% of the time i can increase rpms and get the charging to kick back on and run 13.8-14 for 30 minutes or until i shut it off
then sometimes that does not work
this seems to me more like a voltage regulator than bcm???? but i dont know

it will run, start and stop fine for 30-40 minutes and then i can watch it start dropping and go down to 12.2-12.4 etc
sometimes turning the car off and back on makes it charge again sometimes it just starts again on its own

it has to be dropped to 12.2 for a bit before it pulls the red dash visit workshop code, sometimes it will drop and then kick back in itself and no red light comes on

i am debating just replacing bcm and the relays- confused on the relays is it K57 or K75 or both?
also does anyone know the last interation of the bcm?
i ask husker for one and they said no longer available and gave me this number which all the sites say are not compatible with my car 251 545 37 32
the one in the car now is 211 540 86 45
would like to try and buy the newest one

any input on all this would be great

E55Greasemonkey

Unplug the bcm (the wiring harness to the car not the big wire), let it sit 30 minutes then reconnect it and see if the problem resolves itself. Note: your main 12v battery should remain connected the entire time and key should be out of the ignition.

clvincent

did that already and did not solve the problem, but may try it one more time