C.A.R.B. and the Aftermarket
Modifying or tampering with a vehicle's engine can reduce the functionality of its emission controls. As such, California and CARB have established an anti-tampering law, Vehicle Code Section 27156 (VC 27156). The act of adding any aftermarket part, including a cold air intake, is considered an act of tampering with a smog-controlled engine. In other words, you could be breaking California law by adding an aftermarket cold air intake onto their vehicle, unless that cold air intake has received a CARB-issued exemption.
CARB Certification
Getting an aftermarket engine part to meet CARB certification is a costly and lengthy process. An aftermarket product that has been CARB-certified has been thoroughly evaluated and tested to prove that it is reliable and won't increase a vehicle's harmful emissions. CARB-certified aftermarket products will have a sticker or badge with a number detailing its Executive Order (EO) exemption status. This EO number will show smog control technicians, members of law enforcement and others that the part does not violate VC 27156.
Importance of Certification
In order to pass California's smog check requirement, engines must pass both a visual inspection and a "sniffer" (emissions measuring) test before it is allowed to legally drive on public roads. A cold air intake without a CARB-approved EO number will not pass a visual smog inspection. This means that the car will not be legally allowed to drive on the road until the intake has been replaced with a CARB-approved part, even if the sniffer test is clean. Law enforcement officers can also issue citations should they determine and confirm that a vehicle is running without a CARB-approved cold air intake.