Cal. Veh. Code § 9104

The fees specified in this code except fees for duplicate plates, certificates, or cards need not be paid for any vehicle of a type subject to registration under this code owned by a public fire department organized as a nonprofit corporation and used exclusively for firefighting or rescue purposes or exclusively as an ambulance, nor for any vehicle owned by a voluntary fire department organized under the laws of this state and used exclusively for firefighting or rescue purposes or exclusively as an ambulance.