Please read this thread:
Is this the infamous SBC impending failure warning?
I replaced the SBC module, and it is not as expensive or as hard as I thought it would be. If your SBC module is nearing the end of it's serviceable life, it would be wise to have it replaced. There is many things I like about the W211 platform, but the SBC (MY 2003-2006) is NOT one of them. MB went back to regular ABS in MY 2007 in the W211, and has not used SBC since. Having this problem in no way warrants getting rid of the car. Many have done this though......Rich