See https://wordpress.stackexchange.com/a/388108 for details.

functions.php

<?php
/* NOTES:
 * 1. I used $post_ID and not $post_id just because WordPress uses the uppercase
 *    "ID" and not "id". I also used the second parameter passed to the function,
 *    i.e. $post.
 *
 * 2. If your code still doesn't work, post a copy of the code on Pastebin.com or
 *    GitHub.com.
 */
add_action( 'save_post_cars', 'wpse_387941_set_slug', 10, 2 );
function wpse_387941_set_slug( $post_ID, $post ) {
	$meta = array(
		get_post_meta( $post_ID, 'maker', true ),
		get_post_meta( $post_ID, 'model', true ),
		get_post_meta( $post_ID, 'year', true ),
	);

	$new_slug = implode( '-', array_filter( $meta ) );
	if ( strtolower( $new_slug ) === $post->post_name ) {
		return;
	}

	// unhook this function to prevent infinite loop
	remove_action( 'save_post_cars', 'wpse_387941_set_slug', 10 );

	wp_update_post( array(
		'ID'        => $post_ID,
		'post_name' => $new_slug,
	) );

	// re-hook this function
	add_action( 'save_post_cars', 'wpse_387941_set_slug', 10, 2 );
}