For example, in some states, if the vehicle is held in a tenancy in common, rather than a joint tenancy, the deceased person's share of the vehicle may pass to their heirs or beneficiaries. Additionally, if the deceased person had a valid will, they may have left the vehicle to someone other than the surviving owner.
If you have any questions about who owns a vehicle after one of the owners dies, you should consult with an attorney in your state.