California Code, Vehicle Code - VEH § 9250.13

(a)(1) In addition to any other fees specified in this code and the Revenue and Taxation Code, a fee of eighteen dollars ($18) shall be paid at the time of registration or renewal of registration of every vehicle, except vehicles described in subdivision (a) of Section 5014.1, subject to registration under this code, except those vehicles that are expressly exempted under this code from the payment of registration fees.

(2) In addition to the fee required under paragraph (1), upon the implementation of the permanent trailer identification plate program, and as part of the Commercial Vehicle Registration Act of 2001 (Chapter 861 of the Statutes of 2000), all commercial motor vehicles subject to Section 9400.1 shall pay a fee of six dollars ($6).