Essentially, the main procedures of a smog check includes:
- Emissions inspection
- Tailpipe excess smoke test
- Visual inspection
- Functional inspection
- EVAP functional test (most 1995 and older vehicles)
It must be performed in that order as required by the California state.
The emissions inspection is done by an exhaust gas analyzer, also called a smog machine. The machine will test your exhaust gases for three basic chemicals: carbon monoxide, nitrous oxides and hydrocarbons, all bad for our environment.
The smoke test is performed immediately after the emissions test. The smog technician visually inspects for excess black or white smoke at the tailpipe.
During the visual portion of the smog inspection, the smog technician must locate and verify that all emissions components are present and properly connected. Any defective, missing, modified, disconnected emissions components will fail the smog test.
The functional inspection is mainly conducted by the smog technician, and is hands-on. The smog technician will insure proper operation of ignition timing, check engine light, gas cap, filler neck, and exhaust recirculation system (EGR).
For most vehicles 1976 to 1995, an additional test (EVAP Functional Test) must be performed. A separate EVAP machine is used to apply low pressure into the evaporative system (fuel tank, charcoal canister, vapor hoses, etc) in order to detect any fuel vapor leaks.
Your car has to pass all of these tests in order for it to receive a certificate of compliance.
There are many different versions of the smog test:
- Basic Smog Test: This test is required in certain areas of California that have low smog pollution. The emissions inspection is performed at two speeds; idle and 2500 rpm with the wheels stationary.
- Enhanced Smog Test: This test is required in areas where pollution rates are higher than average. This test includes the use of a dynamometer to simulate actual real world emission production of the vehicle tested at 15 mph and 25 mph under load.
- Change of Ownership: This test is required in counties where the smog pollution is even lower and the test is only required when a vehicle is bought or sold or when a used vehicle is imported into California.
- OBDII Smog Machine Link: This test basically means that your car, 1996 or newer, must be able to connect directly to the smog machine via the cars data link connector. This test will pull any trouble codes the car has and any “Readiness Incompletes” stored in the car’s computer.
- Out-Of-State Vehicles: These cars need to be tested in California because the guidelines are different in California than they are in the rest of the country. New cars are exempt from this test as they have already been tested by the manufacturer but used cars imported into California will need to be smog tested.