Cal. Civil Code § 1793.26

(a) Any automobile manufacturer, importer, distributor, dealer, or lienholder who reacquires, or who assists in reacquiring, a motor vehicle, whether by judgment, decree, arbitration award, settlement agreement, or voluntary agreement, is prohibited from doing either of the following: (1) Requiring, as a condition of the reacquisition of the motor vehicle, that a buyer or lessee who is a resident of this state agree not to disclose the problems with the vehicle experienced by the buyer or lessee or the nonfinancial terms of the reacquisition. (2) Including, in any release or other agreement, whether prepared by the manufacturer, importer, distributor, dealer, or lienholder, for signature by the buyer or lessee, a confidentiality clause, gag clause, or similar clause prohibiting the buyer or lessee from disclosing information to anyone about the problems with the vehicle, or the nonfinancial terms of the reacquisition of the vehicle by the manufacturer, importer, distributor, dealer, or lienholder. (b) Any confidentiality clause, gag clause, or similar clause in such a release or other agreement in violation of this section shall be null and void as against the public policy of this state. (c) Nothing in this section is intended to prevent any confidentiality clause, gag clause, or similar clause regarding the financial terms of the reacquisition of the vehicle.