The Mercedes ML320 uses a programmable key fob connected to the key so that the car can be locked and unlocked remotely. If a new key is acquired to use with the car, the key fob will need to be reset so that it can work with that individual car. The fob may also need to be reset after a battery has been replaced.
Insert the key into the ignition.
Press and hold the "LOCK" button on the key fob.
Remove the key from the ignition. Keep the "LOCK" button held down while removing it.
Press and release the "UNLOCK" button five times.
Release the "LOCK" button. The fob is reset.