Diesel Vehicles and Aftermarket Parts
Diesel-powered vehicles were incorporated into the Smog Check Program effective January 1, 2010. Diesel Smog Check inspections include a visual, OBD, and visible smoke test. During the visual test, the vehicle is inspected for any non-California Air Resources Board (ARB) approved emission related aftermarket parts.
California Vehicle Code (VC) section 27156, in part, prohibits modifications to emission control devices or systems without an exemption from ARB. Accordingly, aftermarket parts that modify or affect the original emission controls must be exempted through an ARB Executive Order (EO). In general, modified and add-on parts require an EO exemption. Replacement parts and consolidated parts do not require an exemption. EO numbers for ARB approved parts are specified on an aftermarket parts label that is affixed or stamped on or near the approved part.
Modified parts are any aftermarket part intended to replace an original equipment emission-related part and is not functionally identical to the original equipment part in all respects which in any way affect emissions, excluding consolidated parts. Examples of modified parts include aftermarket performance engine control unit reprogrammers, fuel injection components, and turbochargers.
Add-on parts are aftermarket parts that are not a modified part or replacement part. For the purposes of a Smog Check inspection, add-on parts that could adversely affect the effectiveness of the vehicle's emission controls must have an ARB exemption. Examples of add-on parts include inline programmers, nitrous oxide kits, and propane kits.