Health & Saf. Code, § 43659

(a) The state board shall annually review the requirement that an exhaust device be installed on every 1955 through 1965 model year light-duty motor vehicle upon initial registration, upon transfer of ownership and registration, or upon registration of a motor vehicle previously registered outside this state, to determine the contribution of that requirement to the maintenance of required ambient air quality standards in those air basins where the requirement is applicable.

(b) In making its determination, the state board shall consider all relevant factors, including, but not limited to, the fact that the requirement is being imposed on a constantly decreasing number of motor vehicles.

(c) Upon a determination by the state board by regulation that the requirement is no longer a significant factor to the maintenance of required ambient air quality standards in any applicable air basin, except as provided in subdivision (d), 1955 through 1965 model year light-duty motor vehicles in that air basin shall no longer be required to be so equipped.

(d) All 1955 through 1965 model year light-duty motor vehicles equipped with an exhaust device pursuant to the requirement prior to the adoption of the regulation by the state board pursuant to subdivision (c) shall continue to be so equipped.