The ESP and BAS warning lights may illuminate due to a failed brake light switch. Replacement of the failed switch should correct this concern.Google+
Car Problem Reports
Mercedes-Benz SLK230 Brake Light Switch Failure May Cause ESP/BAS Warning Lights
Mercedes-Benz SLK230 Problem
Average Mileage: 93,108 mi (70,000 mi - 118,000 mi)
Visitor, 2003 Mercedes-Benz SLK230, 112,000 mi
car brakes too right side and esp/bas light comes on
Just replace the brake light switch. It's a pain to do but with patience it solves the problem.