The camshaft adjuster solenoid (which is related to the variable valve timing system) may fail or timing chain/balance shaft components may wear, resulting in illumination of the Check Engine Light and various drivability issues. Mercedes-Benz has released a service bulletin outlining specific repair instructions depending on fault codes stored.Google+
Car Problem Reports
Mercedes-Benz E550 Camshaft Adjuster Solenoid Failure
Mercedes-Benz E550 Problem
Average Mileage: 46,666 mi (20,000 mi - 70,000 mi)
Visitor, 2010 Mercedes-Benz E550, 20,000 mi
I complained to dealership 6 times about problem and light still comes on.... Less frequently now but problem still exists.