Problem with AJAX in wordpress plugin

After Milo’s tutorship:

I recommend first reading how to use AJAX in Plugins properly. – Milo
yesterday

and reading another questions on wp.stack, my problem was solved)

Here is an examples of code from my rewritten files
1)get_state.php:
ad

add_action( 'wp_ajax_ajax_object', 'ajax_handler' );
add_action( 'wp_ajax_nopriv_ajax_object', 'ajax_handler' );

function ajax_handler() {
    global $wpdb, $results, $info, $data, $retval, $result_bikes;
    $excel_out = $wpdb->prefix.excel_out;
    if(!empty($_POST['MARCA']) && empty($_POST['engine'])) {
        $q = ("SELECT DISTINCT engine FROM $excel_out WHERE Brand = '".$_POST['MARCA']."'");
        $results = $wpdb->get_results($q);
        $info = 'Select Engine';
        $data="engine";
    }
    if(!empty($_POST['MARCA']) && !empty($_POST['engine'])) {
        $q = ("SELECT model FROM $excel_out WHERE Brand = '".$_POST['MARCA']."' AND engine="".$_POST["engine']."'");
        $results = $wpdb->get_results($q);
        $info = 'Select Model';
        $data="model";
    }
    if(!empty($_POST['MARCA']) and !empty($_POST['engine']) and !empty($_POST['model'])) {
        $q = ("SELECT year, Meiwa_air, oem_air, note_oil, meiwa_oil_black, oem_oil, meiwa_oil_crome, oem_crome FROM $excel_out WHERE Brand = '" . $_POST['MARCA'] . "' AND engine="" . $_POST["engine'] . "' AND model="" . $_POST["model'] . "'");
        $results = $wpdb->get_results($q);
        $info = 'Select year';
        $data="year";
    }
    if(!empty($_POST['filtr'])) {
        $q = ("SELECT `Brand`, `engine`, `model`, `year` FROM $excel_out WHERE `meiwa_oil_black` = '".$_POST['filtr']."'");
        $result_bikes = $wpdb->get_results($q);
    }
    if(!empty($_POST['img_filter'])) {
        $source = WP_PLUGIN_URL .'/oil-filters/MIW 600/'.$_POST['img_filter'].'.jpg';
        echo $source;
    }

    if($results) {
        echo '<option value="">'.$info.'</option>';
        foreach ($results as $state) {
            $retval="<option value="";
            if($data == 'year') {
                $retval .= $state->Meiwa_air.'@'.$state->oem_air.'@'.$state->note_oil.'@'.$state->meiwa_oil_black.'@'.$state->oem_oil.'@'.$state->meiwa_oil_crome.'@'.$state->oem_crome;
            } else {
                $retval .= ''.$state->$data.'';
            }
            $retval .= '">'.$state->$data;
            $retval .= '</option>';
            echo $retval;
        }
    }

    if($result_bikes){
        $brand = '';
        foreach($result_bikes as $bikes){
            if($brand != $bikes->Brand){
                echo "<h3>".$bikes->Brand."</h3>";
            }
            $brand = $bikes->Brand;
            echo '<p>'.$bikes->engine.' - '.$bikes->model.' - '.$bikes->year.'</p>';
        }
    }
    wp_die();
}

2)script.js:

jQuery(document).ready(function($){
    jQuery('#bike-name-list').on('change', function () {
        var b = jQuery('#bike-name-list').val();
        jQuery.ajax({
            type: 'POST',
            url: ajax_object.ajaxurl,
            data: {
                'action': 'ajax_object',
                'MARCA': b
            },
            success: function (data) {
                $("#engine").html('');
                $("#engine").html(data);
            }
        });
    });

    jQuery("#engine").on("change", function () {
        var b = jQuery("#bike-name-list").val();
        var e = jQuery("#engine").val();
        jQuery.ajax({
            type: "POST",
            url: ajax_object.ajaxurl,
            data: {
                'action': 'ajax_object',
                'MARCA':b,
                'engine':e
            },
            success: function (data) {
                jQuery('#model').html('');
                jQuery('#model').html(data);
            }
        });
    });

    jQuery("#model").on("change", function () {
        var b = jQuery("#bike-name-list").val();
        var e = jQuery("#engine").val();
        var m = jQuery(this, "#model").val();
        jQuery.ajax({
            type: "POST",
            url: ajax_object.ajaxurl,
            data: {
                'action': 'ajax_object',
                'MARCA': b,
                'engine': e,
                'model': m
            },
            success: function (data) {
                jQuery("#year").html('');
                jQuery("#year").html(data);
            }
        });
    });

    jQuery("#year").on("change", function () {
        var y = jQuery("#year").val();
        if(!y)
            return false;
        var y = y.split('@');
        if(y[3]) {
            jQuery("#filter_number").val(y[3]);
            jQuery.ajax({
                type: "POST",
                url: ajax_object.ajaxurl,
                data: {
                    'action': 'ajax_object',
                    'img_filter': y[3]
                },
                success: function (data) {
                    jQuery("#drawing").attr('src', data);
                    console.log(data);
                }
            });
        }
        showInfo();
    });

    jQuery("#show_button").on('click', function () {
        showInfo();
    });

    jQuery("#filter_number").on("keyup", function () {
        var d = jQuery("#filter_number").val();
        if(d != null && d != '') {
            jQuery.ajax({
                type: "POST",
                url: ajax_object.ajaxurl,
                data: {
                    'action': 'ajax_object',
                    'img_filter': d
                },
                success: function (data) {
                    jQuery("#drawing").attr('src', data);
                    console.log(data);
                }
            });
        }
    });
});

function showInfo(){
    var name = jQuery('#filter_number').val();
    if(name.length < 5)
        return false;
    jQuery.ajax({
        type: "POST",
        url: ajax_object.ajaxurl,
        data: {
            'action': 'ajax_object',
            'filtr': name
        },
        success: function(data){
            jQuery(".bikes").html('');
            jQuery(".bikes").html(data);
        }
    });
}