La. Stat. tit. 9 § 4790
An obligee who has a judgment ordering the payment of past due child support may file the judgment with the office of motor vehicles in accordance with R.S. 32:708.1 and subject to the provisions of R.S. 13:3881. The judgment, when filed, shall operate as privilege on any titled motor vehicle, as defined in R.S. 10:9-102(d)(19), owned by the support obligor at the time deficient child support judgment is filed with the office of motor vehicles, and shall not affect liens, privileges, chattel mortgages, or security interests as provided in R.S. 10:9-101 et seq. or mortgages already affecting or encumbering the motor vehicle at the date of the filing. The motor vehicle shall be subject to seizure and sale for the payment of the judgment according to the preference and rank of the privilege securing its payment. The privilege for child support shall be legally subordinate to motor vehicle purchase money security interests.
La. R.S. § 9:4790