You can use the_post_modified()
function if you're in The Loop. The modified date will change any time the post is changed in any way / updated in any way.
Update
Ok, lets run a small query, what this does is pulls the latest post, modified or new. Since it's just 1 post we can just check if it has posts, and get the first posts modified date.
<?php
$latest = new WP_Query(
array(
'post_type' => 'car',
'post_status' => 'publish',
'posts_per_page' => 1,
'orderby' => 'modified',
'order' => 'DESC'
)
);
if($latest->have_posts()){
$modified_date = $latest->posts[0]->post_modified;
}
?>
For a full list of Date Format Options, View Codex. If you're using it outside The Loop, you can use get_the_modified_date()
function. Hope it helps!