Certain Mercedes-Benz vehicles, including the ML320, require the driver to input a ratio code before being able to operate the radio. A radio code ensures that someone who steals the vehicle cannot use the radio. The directions for entering a radio code are generally the same for all Mercedes models. The only difference is the location of the numbered buttons on the radio. Not all Mercedes radios require a code before use.
Locate your ML320's radio code. This can be found in the owner's manual that was given to you at the time of purchase. If you cannot find your radio code, contact your nearest Mercedes dealership. Provide your vehicle's VIN and proof of ownership, and the dealership should give you the radio code.
Turn on your vehicle.
Enter your radio code once the radio screen displays a phrase similar to "Enter Radio Code". Use the radio buttons labelled with a number to enter your code. Once the correct code is entered, the radio will unlock and become usable. If the radio does not unlock automatically, press the "seek" button after entering the code.