Legal Question in Intellectual Property in California

Your question is unclear. Do you mean that your ex-girlfriend is buying the vehicle from you in installments? Or do you mean she is paying off a loan you took from a third party to purchase it? (What do you mean by "restraining to do so"?) Without knowing exactly what the details are, it is impossible to give a definitive answer. Here are, however, a few legal principles.

Generally, the person whose name is on the title is the owner of the vehicle, even if someone else is paying the loan on the vehicle. (Sometimes parents will pay the loan on a child's first car, but put the title in the child's name.) Usually, the loan company places a lien on the vehicle, so clear title doesn't actually vest until the final payment is made, and both the owner's and bank's names appear on the registration.

In a private purchase, the title may remain with the previous owner until a loan is paid off, but usually there is a purchase agreement that specifies when the title transfers. Generally, if a purchaser makes all the payments on time, a seller can't refuse to transfer title and the purchaser would have a claim on the vehicle and could prevent the seller from repossessing it. Title is transferred by filling out and signing the transfer portion on the reverse of the title and filing that with the DMV.

Once title has transferred, the title holder owns the vehicle, regardless of whether payments have been made. If there is a contract, however, the seller could sue for money damages if full payment is not made and may be able to reclaim the vehicle to satisfy a judgment.

If your ex-girlfriend has been making payments and has the vehicle in her possession, it is doubtful you could reclaim it without reimbursing her for the payments unless there is a written agreement that says otherwise.