This BAS/ESP is driving mad, I have read just about every thread here and on the benz forums regarding this issue. At first it was intermittent and the reset procedure would fix it then it was constant and reset would not clear it. No codes were present, had the brake fluid changed and the light went out for a few days. Then it came back with 2 codes.

c1010 CAB system under voltage
c1200 brake lamp switch circuit

Changed the battery and brake lamp switch even though I was not having any of the other problems associated with them. No change light is still on, had the shop clear the codes drove it for a while then took it back to check for codes. Seven codes now.

c1010 CAB system under voltage or according to some lists battery system low
c1100 left front wheel speed sensor
c1140 steering angle sensor
c 1529 undocumented (on their scanner)
c1202 release switch plausible
c1025 can signal
c1332 bas solenoid valve circuit

At least some of the codes now point to known fixes but damn, what a pain.
Alternator tests good by the way.