An emissions test is a test that measures the level of pollutants released by a vehicle to ensure that it falls within the greenhouse gases and pollutants standards set by the Environmental Protection Agency (EPA) . The test is also known as a smog check and is required by law in many states in the US. The test can potentially review the levels of carbon dioxide (CO2), hydrocarbons (HC), carbon monoxide (CO), oxides of nitrogen (NOx), and other emissions coming from the vehicle. The test can take between 15 to 30 minutes, depending on the states requirements. There are different types of inspections that can check a vehicles emissions, but the most common types are:

• On-Board Diagnostics Generation II (OBDII) Inspection: This test checks that the vehicle is running to its standards by tapping into its computer system. If any issues are detected, the vehicle will fail the test.

• Two-Speed Idle (TSI) Test: This test is generally reserved for older cars and tracks exhaust emissions.

• Acceleration Simulation Mode (ASM) Test: This test is used for newer cars and measures emissions while the vehicle is accelerating.

During the test, the vehicles emission system will be visually inspected to ensure that it is operating properly and reducing the harmful gases that escape into the air. The emission system can sustain wear-and-tear with every mile driven, so it is important to keep it properly maintained to pass the test. If the vehicle fails the emissions test, it may not be able to become registered or, if already registered, the registration may not be renewed.