I have a 2006 E55 with the red battery light on. I scanned with xentry and have no communication to the battery control module. Merc no longer has these in stock so I ordered a used one from fleabay. Do I need to virginize/code the replacement?

 

If it is chosen correctly, it does not need any coding.

 

Try resetting the BCM first. Tech bulletin below.

 

what is a circuit 30 reset

 

Circuit 30 is constant power. You are disconnecting the BCM from its constant power supply; sort of like a "hard" reboot on a computer.
Circuit 15 is switched power; there are several subcircuits (e.g. circuit 15R) that activate in sequence as the system comes online.

 

so circuit 30 reset is just disconnecting both batteries for a few minutes?

 

Correct.
Errata; Circuit 30 is unfused; direct connection between battery and module (alternator). Circuit 30U is fused; direct connection to the battery but with a fuse inline (starter motor on some models). The latter is primarily the diesel versions of the W211 which use a 250 amp fuse in the harness. The schematics for the W211 E55 (U137 - applicable to the M112 and M113 engines) do not show a fuse inline. So...multiple versions of the schematics depending upon version and always fun (not!) to work through trying to understand the circuitry.