To avoid damage to your vehicle when using a car wash, ensure the following beforehand: 
 If you would like to leave the vehicle while it is being washed, make sure the SmartKey is located in the vehicle. The P gear is otherwise automatically engaged. If, after the car wash, you remove the wax from the windshield and wiper rubbers, this will prevent smearing and reduce wiper noise.  | 
Mercedes-Benz C-Class (W205) 2015 - 2021 Owners Manual > Airbags: Limited protection from airbags
    WARNING Risk of injury due to modifications to the airbag cover If you modify the cover of an airbag or affix objects such as stickers to it, the airbag may no longer function correctly. Never modify the cover of an airbag and do not affix objects to it. The installation location of an airbag is id ...