DataGridCheckBoxColumn binding Mode twoWay my database is not updated

I am trying to do to a Bingding from my database to my DataGridCheckBoxColumn. If i do some change in my DataGridCheckBoxColumn my databse is not updated.

XAML code Binding="{Binding Path= TLV, UpdateSourceTrigger=PropertyChanged, Mode=TwoWay}" IsReadOnly="False"/>

viewModel public bool? TLV { get { return _terminal.TLV; }

        set
        {
            if (_terminal.TLV != value)
            {
                _terminal.TLV = value;
                //RaisePropertyChanged("TLV");
                NotifyPropertyChanged("TLV"); 
            }
        }
    }