Normal programming of the radio security code follows these steps. 1) turn key on 2) turn radio on 3) word code should be displayed 4) enter 5 digit radio code and enter, radio should operate. If you have tried this three times consecutively without success, wait may be displayed, you will have to leave the key on for a period of time until "code" is displayed again. You may need to connect a battery charger, because it may take an hour to do so. If this fails again, you may have the wrong code and you will have to get the proper code from your MB dealer, (they will need to remove the radio and get the serial number from the radio chassis). If you have had radio repairs before they may have not updated the radio code.