Cal. Veh. Code § 40807
No record of any action taken by the department against a person's privilege to operate a motor vehicle, nor any testimony regarding the proceedings at, or concerning, or produced at, any hearing held in connection with such action, shall be admissible as evidence in any court in any criminal action.
No provision of this section shall in any way limit the admissibility of such records or testimony as is necessary to enforce the provisions of this code relating to operating a motor vehicle without a valid driver's license or when the driving privilege is suspended or revoked, the admissibility of such records or testimony in any prosecution for failure to disclose any matter at such a hearing when required by law to do so, or the admissibility of such records and testimony when introduced solely for the purpose of impeaching the credibility of a witness.
Ca. Veh. Code § 40807