Problem with JSON, Access and Special characters in CodeIgniter

I expose the environment first:

• 1 Database in msAccess
• 1 Web server with a REST API generated in codeIgniter, which returns a JSON with the contents of a query to the database Access.
• 1 Postman to check requests.

When in one of the fields of the database that the JSON returns there is a special symbol (Ø, ", etc ...) the generated json is not valid (I think) and in postman it does not give me any results, or any error, it just comes out empty.

If I modify the special character in the database (ex: if it is Ø I remove it and write a diameter), the same request works correctly ...

The connection is through ODBC, in UTF-8 format,

I put a query of those made, but I think the problem is not there because depending on the content of the database works or not.

public function list_minimos_get(){

        $query = $this->db->query("SELECT F_STO.ARTSTO, F_ART.DESART, F_ART.EQUART, F_STO.MINSTO, F_STO.ACTSTO
                FROM (F_STO
                      LEFT JOIN F_ART ON F_STO.ARTSTO = F_ART.CODART)
                      WHERE F_STO.ACTSTO<F_STO.MINSTO
                      AND F_STO.ARTSTO LIKE 'T%';
                 ");    

        $respuesta = array(

            'error' => FALSE,
            'stock' =>  $query->result_array()
        );


        $this->response($respuesta);


  }

The truth is that I do not know where to go ... I hope you can give me a cable. Thank you very much.