Doubt when returning string json for FullCalendar event

I have a question. I'm using FullCalendar in a project. I can display the data registered in the bank normally.

My problem is in the eventClick: I did so:

var date = new Date();
    var d = date.getDate(),
            m = date.getMonth(),
            y = date.getFullYear();
    $('#calendar').fullCalendar({
        header: {
            left: 'prev,next today',
            center: 'title',
            right: 'month,agendaWeek,agendaDay'
        },
        buttonText: {
            today: 'today',
            month: 'month',
            week: 'week',
            day: 'day'
        },
        eventClick: function (event, jsEvent, view) {
            $.ajax({
                type: "POST",
                dataType: "json",
                url: '<?php echo base_url(); ?>' + 'agenda/get_dados_evento/',
                data: event.id,
                async: true,
                success: function (response) {
                    $("#evento").html(response.id_carro);
                    $("#modal").modal();
                }
            });
        },
        //Random default events
        events: <?php print_r($eventos); ?>,
        editable: true,
        droppable: true, // this allows things to be dropped onto the calendar !!!
    });

When I click on an event registered in the calendar, the event.id is sent to the controller

function get_dados_evento() {

    $id_agenda = $this->input->post('id');
    //$id_agenda = '24';

    $query = $this->model_agenda->get_dados_evento($id_agenda);

    echo json_encode($query->result());
}

Here is the model:

function get_dados_evento($id_agenda){

    $this->db->select(""
            . "agenda.id as id_agenda,"
            . "agenda.id_carro as id_carro_agenda,"
            . "agenda.title as titulo_agenda,"
            . "agenda.start as dt_inicial,"
            . "agenda.end as dt_final,"
            . "agenda.dt_cadastro as data_cadastro_agenda,"
            . "carro.id as id_carro,"
            . "carro.modelo as modelo_carro,"
            . "carro.placa as placa_carro,"
            . "carro.fabricante as fabricante_carro,"
            . "carro.tipo as tipo_carro,"
            . "carro.ano_fabricacao as ano_fabricacao_carro,"
            . "carro.kilometragem as kilometragem_inicial_carro,"
            . "carro.status as status_carro,"
            . "carro.dt_cadastro as data_cadastro_carro");
    $this->db->where('agenda.id', $id_agenda);
    $this->db->join('carro', 'agenda.id_carro = carro.id', 'inner');
    $query = $this->db->get('agenda');

    return $query;
}

My problem is when displaying the information in the view ... if I put the following code in block success:function(response){ console.debug(response); } it prints the object. And at the time I try to display console.debug(response.id_carro); it is undefined