In California, there are as many as five different types of smog check stations. However, there are essentially two differences: ones that can repair your vehicle and others that can only perform the emissions test. Let's start by going over the different types of shops in California.
Test Only Station
Test only stations are licensed by the state of California to perform only tests on vehicles. They are prohibited from performing any repair services. Gross Polluters can be certified at these stations. Potentially high-polluting vehicles also known as gross polluters in the state's smoggiest regions are directed to these shops for their initial inspection, as specified on the Department of Motor Vehicles registration renewal form. In addition to gross polluters, regular vehicles are randomly chosen to have their test at test only shops. An oil change is not considered a repair service so many test only stations will offer oil changes as an extra service.
Test and Repair Station
Test and repair shops are licensed by the state to provide smog tests and repairs to most vehicles. Under current law, test and repair shops are prohibited from certifying repaired gross polluters or vehicles that have been directed to test only stations for inspection. Vehicles that are not gross polluters or selected to perform a test only can be brought to a test and repair station to complete their smog test. The test and repair station can both test and perform maintenance and repairs to your vehicle in order for it to pass the smog check. However, only test only shops and Gold Shield shops are able to certify repaired gross polluters.
Gold Shield Stations
Gold Shield shops are licensed test and repair shops that have received additional certification by Bureau of Automotive Repair (BAR). In addition to the services provided by regular test and repair stations, Gold Shield stations can certify vehicles identified as gross polluters. They can also perform the "after repairs" certification of vehicles directed to test only stations for an initial inspection, as long as the Gold Shield station has performed repairs to the directed vehicle. Gold Shield stations also contract with the Bureau of Automotive Repair to perform state subsidized emissions related repairs on vehicles participating in the Consumer Assistance Program. Gold Shield shops located in the Basic program areas of the state can certify Enhanced area vehicles for new and used car dealers who purchase them and offer them for sale in the Basic and Change of Ownership program areas.
To summarize, test only stations can only perform the smog test and cannot perform any repairs to your vehicle. Test only stations can certify gross polluters. Oil changes and minor services are not considered repair service so these services may be offered at test only shops. Test and repair shops can perform any repair service as well as the state emissions test, but they cannot certify gross polluters. Gold Shield shops can perform repair services and are specially licensed by the state to certify gross polluters as well.
