$(document).ready(function() {
    $("#marke").change(function() {
        
        $("#marke option:first").attr("disabled", "disabled");
        
        var fields = $("#smallForm").serialize();    

        $.ajax({
            type: "POST",
            url: "./includes/econsor.usedCars.ajax.php",
            data: (
                {
                    action: "smallForm",
                    fields: unescape(fields)
                }
            ),
            cache: true,
            dataType: "text",
            success: function(data) {
                $("#modell").html(data);
            }

        });
    });
    
    $("#modell").change(function() {        
        $("#modell option:first").attr("disabled", "disabled");
    });
});