Emissions tests measure vehicle pollution and are required every two years in most states. Failing vehicles must be repaired before use. Testing requirements have changed since the Clean Air Act of 1970, and different tests are used based on vehicle age. The I/M 240 test is used for vehicles built between 1981 and 1995, while newer vehicles undergo OBDII testing. Some states require a single-speed idle exhaust test for older vehicles.
Emissions tests are procedures used to measure the amount of pollution emitted into the air by a motor vehicle. Most states require a vehicle to be tested every two years. The main goal of an emissions test is to reduce pollution from vehicles that release hydrocarbons and other pollutants into the air. Vehicles that are tested and fail to meet National Environmental Air Quality Standards (NAAQS) must be repaired before their owners can legally use them. Vehicle emissions testing requirements have changed over the years.
Originally enacted in 1970, the Clean Air Act was amended in 1990 and mandated that areas with lower than normal pollution rates and areas with more than 100,000 people institute vehicle emissions tests. Subsequently, the Environmental Protection Agency (EPA), responsible for administering the Clean Air Act, was required to create standard operating procedures for emissions testing. After issuing its standards in late 1992, all areas requiring emissions testing were forced to use a 240-second inspection and maintenance test (I/M 240).
The I/M 240 test identifies a vehicle’s pollution problems by measuring the amount of hydrocarbons, carbon dioxide, and nitrogen oxides as a vehicle goes through a simulated drive cycle. Drivers must take their vehicle to a test station where they are instructed to drive on a device similar to an automobile treadmill called a dynamometer. Pollution is collected from a vehicle’s tailpipe while it is idling, accelerating, cruising and decelerating.
Vehicle emissions testing changed again in 1995 when the US Congress passed the National Highway System Designation Act. The act barred the EPA from requiring I/M 240 testing. As long as affected areas met NAAQS, states were given the freedom to use whatever technology they preferred to test vehicles. There are different types of emissions tests administered based on the age of the vehicle.
As of August 2009, the most current version of the 240 I/M test is the 93 I/M test, which is primarily used on vehicles built between 1981 and 1995. Vehicles built in 1996 or later usually receive a second diagnostic test on-board generation (OBDII) where information is taken from the vehicle’s computer system. In some states, vehicles older than 1981 require a single-speed idle exhaust test, in which an exhaust probe measures pollutants released into the exhaust.
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