For the repair shop to proceed with the repossession, the repair shop may have to send the owner a notice outlining the outstanding debt and the timeline to satisfy it, in writing, and that if it is not paid, they will move to have it repossessed.
The exact amount of notice that must be provided will depend on whether it is considered “possessory” (with the car), or “non-possessory” (without the car), which involves the lien extending beyond the time that the repair shop has the vehicle in its possession. These rules are complicated, and will vary depending on several factors, so if you intend to utilize the lien law, it is suggested that you consult an attorney.