As of 2015, there are four possible emission testing methods that the Arizona Department of Environmental Quality may use, depending on the type and age of the vehicle. The first type of emissions test, IM 147, is mostly used to test gasoline-powered light duty vehicles manufactured between 1981 and 1995.
The IM 147 emission test, which is used by the Phoenix metro inspection program, involves continually monitoring the exhaust as the vehicle is driven on rollers at varying speeds to simulate normal road conditions.
The second type of test is the Steady State Idle/Loaded test, which involves monitoring the exhaust while the vehicle is idle and again at about 25 to 30 miles per hour, depending on the type of vehicle. The Tucson metro inspection program uses this test for the majority of 1967 to 1995 vehicles, while Phoenix uses this test for 1967 to 1980 heavy duty gasoline-powered vehicles.
For 1996 and newer model light duty vehicles, Arizona generally uses the vehicle's onboard diagnostics system. This involves connecting to the vehicle's computer, which monitors its emissions and can identify any problems.
Arizona has separate emissions testing procedures for all diesel vehicles. All diesel vehicles are tested for opacity, which measures the density of the smoke coming from the exhaust. All light duty diesel vehicles in the state and all diesel vehicles in Tucson are rested under load on a dynamometer, while all heavy duty diesel vehicles in the Phoenix area are tested through a process known as snap acceleration.