owners manual 2011 S550

Use the mechanical key. Found in the smart key. The lock is under the edge of the trunk lid beside the hand latch. Push release catch on smart key in the direction of the arrow and at the same time, remove mechanical key from the SmartKey. If the trunk cannot be unlocked with the SmartKey or KEYLESS-GO, use the mechanical key. If you use the mechanical key to unlock and open the trunk lid, the anti-theft alarm system will be triggered. Take the mechanical key out of the SmartKey. Insert the mechanical key into the trunk lid lock as far as the stop. Turn the mechanical key counter-clockwise from position 1 as far as it will go to position 2. The trunk is unlocked. Turn the mechanical key back to position 1 and remove it. Insert the mechanical key back into the smartkey. If you don't have the mechanical key you will probably need a locksmith. MBUSA link to manuals >> https://www.mbusa.com/en/owners/manuals They now only post the last 10 years I think, but 2012 might be close enough to 2011.

Smart key photo