Legal Question in Real Estate Law in California

The legal answer is that since you are the registered owner but she is claiming the car, she must produce evidence refutting your ownership. Your registeration certificate is proof of ownership. But you need to call the police and see what they are willing to do; they may say it is a civil matter between the two of you and they will not get involved. You would have to convince them that she might become very angry and it could result in a situation of disturbing the peace of the neighbors.

As a practical matter, calling in the police will get very upset with you and she may restrict your seeing your son. Also, if there is no court ordered child support and you are paying less than what the court would probably order [phone up Child Support Services in another county than yours and find out in general what that amount would be], it might trigger her into going to court to get a higher payment rate. Try to reason with her, using some mutual friend if possible, that her having the car is the same as your paying her $X moreper month in child support and yo can not afford to do so and without the car you may lose your job and not be able to pay her any child support.