About Emissions Testing

In most areas of the United States, used vehicles must pass an emissions test in order to obtain or renew valid registration. Although the federal government has established national emissions standards, these standards can still vary among states. The goal of regular vehicle emissions tests is to preserve the quality of the air by minimizing vehicle-related pollution. Read on to learn more about vehicle emissions and how the tests work.

Emissions Standards

Emissions standards in the United States are set by the Environmental Protection Agency, or the EPA. However, because of its extraordinary air pollution issues, California has the permission of the federal government to establish its own more stringent standards. Every state has a choice of either adopting the national standard or the stricter California standard. Currently, 12 states and the District of Columbia follow the more rigorous California emissions standards, which are set by the California Air Resources Board (CARB). The states that adhere to this standard are thus referred to as "CARB" states.

Types of Emissions Tests

Most states use two types of emissions tests, the ASM2 and TSI tests. Each of these is explained in detail below.

  1. ASM2. This test measures emissions during simulated road conditions using a dynamometer. The ASM2 is basically the vehicular version of a stress test on a treadmill. The ASM2 is a relatively inexpensive test that produces very accurate results. If your vehicle emits too much carbon monoxide, oxides of nitrogen, or hydrocarbons, it will fail the ASM2 test. Some states exempt four-wheel drive vehicles from this test, instead subjecting them to the TSI test.
  2. Two-Speed Idle (TSI) test. The TSI tests your vehicle's tailpipe emissions. An analyzer tool measures the exhaust emissions from your car's tailpipe while the engine idles at a high then low speed. This test is intended to measure the variables that contribute to the creation of ground-level ozone that damages lungs. Your vehicle will fail the TSI test if it emits excessive amounts of carbon monoxide or hydrocarbons. This test is reserved primarily for older cars that do not have the technology for a diagnostic vehicle computer system.

Other Emissions Information

You will need to present evidence to the DMV that your vehicle has recently passed an emissions test in order to register your vehicle or renew your registration. Most states have emissions-testing stations conveniently located near large metropolitan areas. Your state may even allow you to complete the registration process at the emissions-testing station. Typically, the fee for an emissions test is very reasonable (around $20 for most states), and there is usually no charge if your vehicle fails the test. Similarly, some states charge for the initial emissions test regardless of whether the vehicle passes or fails, but will not charge the owner if a retest is needed.