California Code, Health and Safety Code - HSC § 43101

(a) The state board shall adopt and implement emission standards for new motor vehicles for the control of emissions from new motor vehicles that the state board finds to be necessary and technologically feasible to carry out the purposes of this division.Before adopting these standards, the state board shall consider the impact of these standards on the economy of the state, including, but not limited to, their effect on motor vehicle fuel efficiency.

(b) The standards adopted pursuant to this section may be applicable to motor vehicle engines, rather than to motor vehicles.