It may be necessary to reset a Mercedes M Class radio should the radio or battery be disconnected or the battery become completely drained. When the radio receives power again, it will be in a locked and unusable state. The LCD display will read "Enter Code." The security code assigned to the vehicle must be entered to reset the radio and unlock it.
Disconnect the negative cable from the battery with a socket wrench and then disconnect the positive cable as well. Wait 30 minutes to allow for the vehicle's emergency power store to discharge completely before proceeding with the project.
Reconnect the positive cable to the positive terminal on the battery with a socket wrench and then reconnect the negative cable to the battery.
Punch in the five number vehicle security code on the radio keypad. The security code is included with the owner's manual.
Call a local Mercedes-Benz dealership and give them the VIN of the vehicle and the radio's serial number to receive the code if the manual cannot be located. The radio's serial number can be found on the identification plate located on the underside of the radio. Pull the knobs off the radio, remove the face plate by prying it off by hand and the radio may be pulled out far enough to read the plate.
