To unlock the fuel filler cap manually (when a single lock fails) turn the key (1) all the way to the right.
If the fuel filler cap latch release device fails to operate from the remote control/console switch (see Section Single lock) open the tailgate, on ML 55 AMG models, remove the spare wheel cover, remove the left side panel of the luggage compartment upholstery and, turning the key (1) all the way to the right, open the cover manually.