What is a Smog Check for a Car?

When people think of smog, they often think of California. The truth is, smog can happen anywhere, though it is more prevalent in big cities. Older cars are more likely to release smog, but newer cars can also release toxins into the air, especially if they are not maintained properly. It is important drivers know about smog checks and why they are so important. With this guide, individuals will learn all they need to know about smog and how it affects car ownership.

What Is Smog?

The term “smog” was first introduced in the early 1900s. It was used to describe a combination of fog and smoke, which caused a great reduction in visibility. Then, smog was common only in industrial areas. Now that more people are using cars, smog is becoming an increasing problem all over the world.

Today, the type of smog that is most often seen is photochemical. Photochemical smog occurs when sunlight reacts with the nitrogen oxides that are released from car exhausts. This type of smog also occurs when reactions happen between volatile organic compounds and sunlight. VOCs are released from gasoline, chemical cleaners, and paint.

Why Was Smog Testing Implemented?

The first smog check program was started in March of 1984. This program was put into place as a result of SB 33, in hopes of reducing smog and the resultant greenhouse gases that continue to cause problems to the environment.

Over the years, changes have been made to the program, though it remains a joint effort between The California Department of Motor Vehicles, the California Bureau of Automotive Repair, and the California Air Resources Board. Although these efforts were started in California, today, there are other states that require smog checks for older vehicles.

What Do Smog Tests Measure?

A smog check involves multiple steps that check the vehicle’s pollution control systems and exhaust. Smog checks include the following.

  • A visual check is conducted on the system and all its components.
  • A functional check is carried out to evaluate the operation of the system’s parts and ensure they are working properly.
  • A check is performed to determine the level of emissions that are coming from the vehicle’s tailpipe.
  • Finally, the smog check also includes a thorough check of the vehicle’s computer and diagnostics system.

The above outlines the basics of a smog check in the state of California. Each state that has implemented smog checks carries out the test differently. Some states perform a smog check along with the general inspection for the renewal of the registration.

What More Should Drivers Know About Smog Checks?

In the state of California, the price of a smog check can vary considerably because the checks are performed by private businesses that have been authorized by the DMV to perform these tests. Drivers can expect the cost of the smog test to range from $30 to $80.

Each state’s requirements for smog checks vary. In the state of California, drivers are required to have a smog check every two years. In the state of Maine, vehicles must go through a smog check annually.

Should a vehicle fail a smog check, the driver will be given a form that details the reasons for the failure. Vehicle owners can take this form to their mechanic to see what repairs are necessary for passing the smog recheck.

How to Reduce Smog

To reduce smog and ensure a vehicle passes a smog check, it is important drivers maintain their vehicles. Keeping up with maintenance and repairs will help to keep the vehicle running effectively and will help to ensure the emissions coming from the exhaust are within the guidelines of the state.

Drivers can also do their part to improve smog by limiting the number of car trips they take. Planning in advance will help individuals to get all their driving done within one or two trips, versus driving several times a day or week.


California is one of several states that require smog checks. These are required for the vehicle to be legally on the road.

Smog checks are regulated by the Environmental Protection Agency. The goal of these checks is to protect the public from greenhouse gasses that are sometimes carcinogenic and to ensure the environment is protected as much as possible.

While these checks can be an annoyance at times, they are meant for the betterment of society as a whole. Before having a smog check carried out, it is wise to take a vehicle to a mechanic for a tune-up and to ensure there is no need for repairs.