Try using this:
$args = array(
'post_type' => YOUR_POST_TYPE,
'meta_query' => array(
array(
'key' => '_wpcf_belongs_marque-type_id',
'value' => $parent_id
)
)
);
In your loop set an else
statement just to sure that you query isn’t returning zero results:
if ( $the_query->have_posts() ) :
while ( $the_query->have_posts() ) : $the_query->the_post();
$output .= '<li class="active-results">' . the_title() . '</li>';
endwhile;
else:
$output="No items here :(";
endif;
Hope it helps.