Test-and-repair stations are licensed by the state to provide Smog Check tests and repairs to most vehicles. Under current law, test-and-repair stations are prohibited from certifying repaired Gross Polluters or vehicles that have been directed to Test-Only stations for inspection. Only Test-Only stations and Gold Shield stations are able to certify repaired Gross Polluters.

Decades ago, California became known as the nation's "smog capital" because of the poor air quality in the Los Angeles basin area. Los Angeles County sits in a "bowl" topped by a layer of air that won't permit heavy particles to break up in the atmosphere.

In the early 1960s, people began to worry about the bad air outside. In 1963, California became the first state to institute emission controls on new vehicles sold in the state.

Since then, California has led the nation in concern for the environment and controlling vehicle emissions. The California Department of Motor Vehicles requires the owners of most cars to adhere to strict emissions regulations in order to register them.

Every other time you renew your vehicle registration you must obtain a "smog certificate"―a printout of your vehicle's emissions test results. You must register your car within 90 days of your emissions inspection.