ABC

Active Body Control (ABC) Fitment

Active Body Control (ABC) is fitted on vehicles with SA Code 487a.

Active Body Control (ABC) Issues

The Active Body Control (ABC) suspension pulsation damper will cause a humming / buzzing noise when not working correctly. If your dampener needs replacing you will hear a howling sound that peaks at 2000 RPM then disappears above that RPM. M-B has a service bulletin about this. See TSB Topic number LI32.50-P-048280 for more detailed information.

Active Body Control (ABC) Pulsation Damper and Filter DIY Repair

http://www.benzworld.org/forums/w220-s-class/1627917-abc-pulsation-damper-filter-diy-repair.html