California Code, Health and Safety Code - HSC § 43646

(a) The bureau, in consultation with the state board, may develop, not later than 180 days from the operative date of this section, a list of engine maintenance practices that are designed to improve a motor vehicle's engine operating efficiency. The bureau shall conduct any evaluations that it determines to be necessary to identify the extent to which various maintenance practices could reduce vehicle emissions, and the minimum periodic application of each maintenance practice that is required to achieve the desired improvement in engine operating efficiency. The bureau may contract with private automotive testing services to carry out the evaluations.

(b) The bureau shall make the list available to the public, and shall specify therein the extent to which each maintenance practice can be expected to reduce vehicle emissions, and how the application of each practice could result in a reduction of the vehicle's smog index.

(c) A motor vehicle owner who subjects his or her vehicle to enhanced maintenance practices, as established by the bureau, may submit the vehicle to an in-use emissions evaluation at a smog check station to determine if excessive in-use emissions have been reduced. If the vehicle is certified as having reduced its emissions relative to its last in-use emissions evaluation, the Department of Motor Vehicles shall adjust the smog index for the vehicle. Vehicles receiving adjustments pursuant to this subdivision shall submit to annual in-use emissions evaluations to maintain their adjusted smog index. A failure to submit an annual in-use emissions evaluation to the Department of Motor Vehicles shall result in the vehicle's smog index being adjusted to its original level.

(d) This section shall become inoperative pursuant to Section 33 of the act adding this section or, in any case, five years from the date determined pursuant to Section 32 of the act adding this section, and on the January 1 following the date upon which this section becomes inoperative, is repealed.