If his name is XXXXX XXXXX title to the vehicle (alone or along with your name), he would have to sign off on the title and bill of sale in order to transfer the vehicle.
You can't sell the vehicle unless you own it outright.
Also, you can't consider this abandoned property if it is left at his house which he owns.
All you can do is file for divorce, claim that you don't know where he is (summons to him will be published), and ask the court in the divorce decree to award you title to the car. Once you're awarded ownership of the vehicle, you can do whatever you want with it.
If you decide to divorce, you should see a local lawyer to handle this because of the notice requirements, etc.
Technically, he didn't abandon it if you agreed to keep it. However, since you can't get in touch with him to remove the vehicle, you can inform your local law enforcement officers that he has abandoned the vehicle and they can come and impound it. Here's the statute: http://law.justia.com/utah/codes/2006/title41/41_04157.html
If he owes you child support, you should file a motion with the court to attach and sell his car to generate money to pay his back child support.
The only way you can sell the car is with a court order, and because you agreed to accept the vehicle, it's going to be hard for you to claim that he abandoned it UNLESS you can get him a written notice that you now consider it abandoned.
However, if he owes you child support, that's a different story. You should be able to get a court order to attach and sell the property in order to pay you child support arrearages.
I think you need a lawyer because he's out of the country - whereabouts unknown. In these cases, there are notice procedures you must go through to ensure that his due process rights are protected. You don't want to miss a step or it could void the entire action.
It's best to hire a lawyer to make sure this is done right. Because this will apparently be uncontested - because he's nowhere to be found - it should not cost too much.
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