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Smog checks are conducted to improve the air we breathe. They are regulated by the Environmental Protection Agency (EPA) of the United States to protect public health and the environment from the effects of air pollution. The primary purpose is to ensure that your vehicle is not emitting harmful elements or chemicals in the environment. Pollutants that smog check facilities look for include carbon dioxide, hydrocarbons, nitrogen oxides, carbon monoxide, and other tailpipe emissions.

Although smog checks began in California in 1984, today, over 30 states in the United States require vehicles to pass smog inspections annually or biannually in order to help control emissions.

What Is a Smog Check?

A smog check is an assessment of a vehicle's emissions-control systems and equipment to measure the level and type of pollutants emitted by the car. It often involves the visual inspection of emissions-control systems and equipment, a functional inspection of the vehicle's check engine light, ignition timing, fuel evaporative system, exhaust gas recirculation system, and gas cap. A smog check also involves tailpipe emissions inspection and functional inspection of the vehicle's onboard diagnostic (OBD) system.

How Long Does a Smog Check Take?

Although a smog check can sometimes finish earlier, it usually takes 20-30 minutes for the test to complete. The duration of a smog test can vary depending on the type and age of the vehicle, the testing equipment used, and the state where you performed the test.

To avoid a long wait at the smog test facility while ensuring you pass the test, you should consider the following recommendations:

  • Clear check engine light: If your vehicle has a check engine light on, you should have it checked by an automobile professional or local auto dealer prior to a smog test. A faulty oxygen sensor is one common reason why vehicles fail a smog test. Usually, before an oxygen sensor failure, the sensor stops regulating the air and gasoline mix ratio, which may lead to a smog check failure
  • Pre-smog test driving: About a week before going for a smog check, it is recommended that you drive your car for a minimum of 30 minutes at highway speeds. This is to get your catalytic converter hot enough to burn off residual oil and gasoline. Also, drive the car for a minimum of 20 minutes before arriving at the smog test facility to ensure the car is well warmed up and operating at optimum level.
  • Get an oil change: Since dirty oil produces high hydrocarbon levels, which are pollutants capable of causing your vehicle to fail a smog test, you should consider having an oil change and ensure your filter is clean before going for a smog check. Also, check fluid levels in the car and the condition of hoses and belts under the hood.
  • Use fuel additives: Good fuel additives can unclog your vehicle fuel injectors if they need cleaning. Note that carbon deposits within the exhaust paths or engine's intake can cause a smog test failure. After adding a fuel additive, drive the vehicle for several miles to ensure the additive has worked its way properly around its path.
  • Choose a good time to visit the smog test facility: Avoid visiting a smog test station at peak periods. Visiting the test facility on a Saturday afternoon may be a bad idea, but an afternoon weekday visit may get you in and out of the smog test facility quicker.
  • Practice regular vehicle maintenance: If you maintain a regular vehicle maintenance routine such as air filter replacements, oil changes, and spark plug replacements, you stand a good chance of completing smog tests quicker than others.
     

How Much Is a Smog Check?

While most smog check prices vary between $20 and $80, some tests may cost up to $150. Note that some states charge an extra certification fee, typically under $10, covering the cost of a certificate or sticker. Smog check price varies depending on several factors, including the type of vehicle, your state, the kind of smog test ordered, and the smog testing facility. In many states in the United States, smog testing facilities charge higher fees to test diesel-powered vehicles than gasoline-powered vehicles.

How Often Do You Need a Smog Check?

How Often Do You Need a Smog Check?

How often you need a smog test depends on the DMV requirements in your state and the type of car you drive. For instance, in Nevada and California, smog checks are required every two years for most cards as part of the vehicle registration process. In some states, smog tests are required as often as twice a year, while in others, smog checks must be done annually. Some states do not require smog tests at all. Regardless of the frequency of smog test requirements in your state, it is recommended that you always keep your car in top condition.

What Do You Need for a Smog Check?

The exact documentation required for a smog test depends on the DMV requirements in your state. However, you should visit a smog test facility with the following:

  • The vehicle to be tested
  • Your driver's license
  • Proof of insurance
  • Vehicle registration
  • Vehicle title
  • Previous smog test results
  • Vehicle registration renewal notice (if applicable).
  • Applicable smog test fee
     

Where To Get a Smog Check

For official smog checks, you must use smog check stations or facilities approved by the Department of Motor Vehicles in your state. You may be able to verify the list of authorized smog check facilities on your state DMV website. Alternatively, consult with friends or family members in your location or contact the DMV for smog test facility recommendations.

Conclusion

A smog check evaluates a vehicle's emissions-control systems and equipment to measure pollutant levels emitted. It is required in many states and involves visual and functional inspections of key parts of the vehicle’s emission control system. A smog test typically lasts 20-30 minutes, and its duration can be influenced by factors such as vehicle type and testing equipment. Costs range from $20 to $150, including additional certification fees in some states.

 You may need to have a smog check conducted on your car every two years or more, depending on the requirements in your state and the type of vehicle that needs testing. Your state DMV or the smog testing station requires specific documentation before you can have the test done. Typically, you will need your driver's license, insurance proof, registration, and vehicle registration renewal notice. To avoid a smog test failure, ensure you carry out routine maintenance and clear any check engine indicators before visiting a smog test facility. Whether your state requires a smog test, keeping your vehicle well-maintained to reduce emissions is in your car’s best interests.

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