What is Emission Testing and Why It Is Important

Emission testing in raleigh

Emission testing for your vehicle is important to you, for your car or truck, and for the environment.  This test indicates the levels of pollutants your vehicle is emitting in order to comply with standards set by the Environmental Protection Agency.

The first emission test was performed in 1966 in California. Now, it is required by law in more than 30 states on regular schedules. If your vehicle fails the emissions test, you must make the appropriate repairs and have the vehicle retested.

In North Carolina, 22 counties require emissions testing annually for cars between 3 and 20 years old. At Reliable Imports, we perform the necessary emission testing as part of the annual inspection on your vehicle. In this article, we wanted to discuss what emission testing is and why it is important.

What is Emission Testing?

Emission tests are standard tests that measure exhaust emission for different types of engines and vehicles. After this test is performed, you know how much pollution your vehicle is producing. In 1990, the Federal Clean Air Act was amended to significantly reduce air pollution. This resulted in the Environmental Protection Agency creating a set of emissions standards to minimize the amount of hazardous air pollutants released by motor vehicles. 

The test indicates levels of hydrocarbons, nitrogen oxide, carbon monoxide, carbon dioxide, and emissions from evaporation. Ultimately, the emissions test ensures that your vehicle is within the EPA standards and is, therefore, limiting its negative impact on the environment. 

Why It is Important to Have the Emissions Tested

When you know that the emissions from your vehicle are in compliance with regulations, you can be assured that it is running efficiently and is safe. You can have peace of mind that the air you and your family are breathing from the automobile is as clean as possible. You can also know that your vehicle isn’t contributing to harmful pollutants that are adversely affecting the environment. Most of the pollutants result from unburned or partially burned fuel that passes through the combustion of the engine while other pollutants are produced from naturally occurring chemical reactions that occur from the temperature and the air mixing together when the vehicle is running.

What is the Emission Test Procedure?

Testing procedures measure your vehicle’s emissions and track the pollutants it releases. The test can take 15 to 30 minutes, depending on the state’s process. There are a variety of inspections that check for your vehicle’s emissions. 

On-Board Diagnostic (OBD) Inspection

The On-Board Diagnostic (OBD) inspection is the most common test for vehicles that are 1996 and later models. It verifies the data from your vehicle’s internal emissions diagnostics system. This test also makes sure that the Check Engine light is working properly.

Acceleration Simulation Mode (ASM) Test

Many automobiles made in 1995 or earlier don’t have an OBD system installed, so the Acceleration Simulation Mode (ASM) test is used. The ASM test uses a dynamometer and a tailpipe sensor to simulate driving conditions in measuring the vehicle’s emissions.

Two-Speed Idle (TSI) Test

The Two-Speed Idle (TSI) test is generally used for older cars. It tracks exhaust emissions when the engine is idling at a high and a low speed.

What If Your Vehicle Fails the Emission Test

If your vehicle does not pass the test, you won’t be able to drive it until you have made the necessary repairs and pass another test. The results of the test will indicate the fixes that you need to make. If Triangle Imports performs the emission test, our mechanics will know exactly what to do in rectifying any problems. Here are some of the common reasons why your vehicle might fail the test:


  • Excessive hydrocarbon or carbon monoxide levels can cause test failure.

  • A leak in the exhaust system or poor engine adjustments means a valid exhaust sample can’t be taken, which causes test failure.

  • OBD emissions control components or the dashboard’s Malfunction Indicator Light (“check engine” light) are malfunctioning.

  • A loose gas cap can cause the test to fail because the seal isn’t tight and is leaking vapors.

  • Missing emissions control equipment is absent or has been disconnected can cause a test to fail.

Call Us to Schedule Your Inspections and Emissions Test

Come to Reliable Imports for your annual inspection and emissions testing. We know your vehicle and can make the necessary repairs if there are any needed. Call us at (919) 324-3019 to schedule an appointment!


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