A: In order for your vehicle to receive a Smog Check certificate, it must pass all the following elements of a Smog Check inspection:

A: The tailpipe test alone cannot guarantee that a car is not emitting harmful amounts of pollutants into California's air. In fact, to obtain a Smog Check certificate, a vehicle must pass all three portions of the Smog Check inspection-the visual, functional and tailpipe inspections (see previous question).

An "underhood" inspection comprises the visual and functional portions of the Smog Check inspection. The visual inspection ensures that the vehicle has all of the proper equipment and that none of its parts are disconnected or modified.The visual and functional tests help identify vehicles with tampered emissions control systems. These vehicles may be configured to pass the tailpipe portion of the Smog Check inspection, but altered later to produce more emissions than allowed. This gave the previous program the reputation of passing vehicles which were "clean for a day," rather than clean until the vehicles' next Smog Check. Vehicles which were only "clean for a day" hindered California from meeting its clean air goals.