Is it permissible to use a car entrusted as an amanah (trust) without its owner's permission, and is it obligatory to return it to its original location, or can it be used out of necessity?

It is forbidden to use a trust without the owner's permission, as this contradicts the very nature of a trust. It must be returned to its place and preserved. What has been done by using it is a sin, unless its owner forgives and permits it.