What Exactly Is a Smog Check?


According to the California Air Resources Board, 400 tons of pollutants that would otherwise be clouding the air are removed every day, thanks to the Smog Check program. The program in California is among the most stringent in the country. Hybrids, electric cars, and vehicles that run on two cylinders do not need to get checked. Motorcycles also do not need to get the inspection.

Brand new cars do not need the check – only when your vehicle is six years or older does it need to have a smog check in California. You have to get the smog check every other year. Cars with a model year preceding 1976 are also excused from getting checks. The DMV will tell you when you are due for a check.

Once you decide to sell your car, the vehicle can only be transferred to a new owner if there is valid proof of a Smog Check by the seller. Under this rule, even cars that are only four years old (or older) must have the check performed. When the sale occurs between certain immediate family members, the inspection may be waived.

Owners are sometimes told on their registration renewal that they can only have their vehicle inspected at a Gold Shield Station or a Test-Only Station. A Test-Only Station is one that is only permitted to test cars and cannot do repairs – this removes the possibility of a testing facility forcing unnecessary repairs at its own shop and ensures transparency.

A Smog Check is performed in two ways – through a TSI Test and an ASM Test. The TSI or Two Speed Idle Test is used to test all-wheel drive vehicles, while the ASM Test or Acceleration Simulation Mode Test tests for nitrogen oxide. The TSI inspection consists of a 2500 RPM test as well as an idle test. The 2500 RPM test runs for 30 seconds, and then the car is shifted to idle. Cars that are overheating or have gas leaks, coolant leaks, or bad brakes cannot be tested.

In the Visual Inspection portion of the check, the technician goes over the crankcase emission controls, thermostatic air cleaner, fuel evaporative system, catalytic converter, ignition spark controls, fuel metering system and air injection system, and several sensors. While the engine is running, the technician looks for fuel leaks and performs a visible smoke test.

If a car fails the visible smoke test, the owner will be given a sheet that indicates if it was because of smoke from the tailpipe or smoke from the crankcase during the visual inspection. These vehicles must be repaired in order to pass a smog check.

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