Cep.php

<?php

class Cep {

public function get_cep_cidade($tId, $city)
  {
		$this->db->select('cep_cidade.nome, cep_estado.id, cep_estado.id_uf');
		$this->db->from('cep_cidade');
		$this->db->join(
			'cep_estado', 
			'cep_cidade.id_uf = cep_estado.id_uf AND cep_cidade.nome = "'.$city.'"', 
			'left'
		);
		$this->db->where('cep_estado.id', $tId);
		$query = $this->db->get();

		if ($query)
		{
			return $query;
		}
		else
		{
			return FALSE;
		}
	}

debug.txt

CI_DB_mysqli_result Object
(
    [conn_id] => mysqli Object
        (
            [affected_rows] => 1
            [client_info] => 5.5.31
            [client_version] => 50531
            [connect_errno] => 0
            [connect_error] => 
            [errno] => 0
            [error] => 
            [field_count] => 3
            [host_info] => Localhost via UNIX socket
            [info] => 
            [insert_id] => 0
            [server_info] => 5.5.32-0ubuntu0.12.04.1
            [server_version] => 50532
            [stat] => Uptime: 38533  Threads: 10  Questions: 5354  Slow queries: 0  Opens: 730  Flush tables: 1  Open tables: 176  Queries per second avg: 0.138
            [sqlstate] => 00000
            [protocol_version] => 10
            [thread_id] => 497
            [warning_count] => 0
        )

    [result_id] => mysqli_result Object
        (
            [current_field] => 0
            [field_count] => 3
            [lengths] => 
            [num_rows] => 1
            [type] => 0
        )

    [result_array] => Array
        (
        )

    [result_object] => Array
        (
        )

    [custom_result_object] => Array
        (
        )

    [current_row] => 0
    [num_rows] => 
    [row_data] => 
)

usage.php

<?php
$result = $this->Cep->get_cep_cidade($location['region'], $location['city']);
print_r($result);
?>