Legal Question in Real Estate Law in California

If all she is on the lease agreement is a co-signer, it is your vehicle. A co-signer is merely someone who agrees to pay if the singer defaults; they have no legal right to the object leased [they might be able to argue they have some weak equitable right but the legal right is superior and overcomes it]. Your real problem is that it is community property since you were paying not with your private funds but community funds. But since she will not pay for the vehicle and it can not be split in two, it would be alright for you to keep the vehicle until their is a divorce agreement as to property rights. To be safe, send her a letter stating why you are keeping the car.

The deciding issue is DMV title. Whomever is listed as the/an owner has a right to posession of the vehicle. It sounds, however, like you should get a divorce or legal separation going to protect your economic rights and credit.