Emissions Testing

Increasing vehicle use in metropolitan Phoenix and Tucson contributes to air pollution that endangers public health. To improve air quality and reduce vehicle emissions in these heavily traveled areas, ADEQ administers a mandatory vehicle emissions testing and repair program known as the Vehicle Emissions Inspection Program (VEIP).

Vehicle emissions testing in Arizona is performed under contract. Our contractor constructs and equips facilities in the emission control areas in which the tests are performed.


  1. IM 147:

    This is the test used for most 1981 thru 1995 light duty (8500 lbs. or less GVWR) gasoline-powered vehicles in the metro Phoenix inspection program. In this test, the vehicle is driven on rollers (called a dynamometer) at varying speeds to simulate urban driving. The exhaust is continuously measured and the results are shown in grams per mile.

  2. Steady State Loaded/Idle:

    This test is used for most 1967 thru 1995 vehicles in Tucson as well as 1967 through 1980 models and newer heavy-duty gasoline vehicles (GVWR higher than 8500 lbs.) in Phoenix. The vehicle is tested at idle and (depending on vehicle class) at approximately 25 to 30 miles per hour. The results are shown in percent or parts per million.

  3. OBD (On Board Diagnostics)

    The newest test to be used in Arizona is the on-board diagnostic test. Used on 1996 and newer light duty gasoline vehicles, engine operating data is accessed by connecting directly to a computer in the vehicle that continuously monitors engine emission control systems operation. The on-board diagnostic test is also used on 1997 and newer light duty diesel vehicles (8500 GVWR and less) in Phoenix. The on-board diagnostic test can identify problems before they lead to engine damage and emissions system failure.

  4. Diesel

    Diesel vehicles other than 1997 and newer light duty diesel vehicles (8500 GVWR and less) in Phoenix are tested for opacity (smoke density). The test uses an opacity meter, which is an instrument that measures the percentage of opacity of the exhaust. In Tucson, duty diesel vehicles up to 26,000 GVWR are tested under load on a dynamometer. Diesel vehicles over 26,000 GVWR are tested using a procedure called snap acceleration. In metro Phoenix, heavy duty diesel vehicles are tested using a procedure called "snap acceleration".

  5. Tampering

    In addition to one of the above tests, a vehicle may undergo a visual inspection to determine the presence of certain emission control components as installed by the manufacturer. Inspection includes catalytic converter, operational air pump, positive crankcase ventilation system and evaporative control system. These inspections coupled with the evaporative system integrity (pressure) test constitute the tampering inspection.

Testing is quick, easy and accurate; however, at certain times of the month backups can occur. For faster service, it is highly recommended that you avoid the end of the month and middle of the day.

Why & How We Do Emissions Testing