All 1967 and newer diesel powered vehicles registered within the emissions control areas of metro Phoenix (Area A) and Tucson (Area B) are required to be emissions tested annually. The only exception is for apportioned vehicles, which are commercial vehicles that are licensed in multiple states. Diesel vehicles pulling trailers will not be accommodated at the inspection stations.

Diesel emissions testing in Pima County and for light-duty (8,500 lbs GVW and less) vehicles in Maricopa County consists of loading the vehicle on a dynamometer and measuring the opacity of the exhaust plume. The measured opacity must not exceed the established maximum. In Pima County the maximum allowable is 30 percent opacity. In Maricopa County the maximum allowable is 20 percent opacity. (The maximum allowable is determined by the average elevation of the registration area).

Heavy-duty (8,501 lbs and greater) diesel vehicles in Maricopa County are tested using the Society of Automotive Engineers J1667 test protocol, commonly referred to as the "snap-acceleration test." The test consists of measuring the opacity of three, wide open throttle, no-load accelerations from idle to maximum governed engine speed with the transmissions in neutral. The average opacity for the three accelerations cannot exceed the applicable standard for the model year of the engine. The maximum allowable for engine model year 1991 and newer is 40 percent opacity, for engine model year 1990 and older the maximum is 55 percent opacity.

Diesel powered vehicles may be tested at any of the vehicle emissions inspection stations in Maricopa County. In Pima County, heavy-duty diesel vehicles (26,000 lbs GVW or greater, or any truck with tandem drive axles) must be tested at 6661 S. Renaissance Dr., Tucson, AZ 85746.

Testing Fees

All diesel vehicles driven on a dynamometer must be operated by station personnel. The driver will be asked to exit the vehicle or move to the passenger seat. Vehicles tested using the snap-acceleration test will be operated by the person delivering the vehicle for testing. In addition to the opacity test, the vehicle will be checked for the presence of an appropriate fuel tank cap.

The owner of a diesel vehicle that has failed the emissions test twice, and who has attempted repairs that meet or exceeded the maximum repair cost limit, can apply for a waiver. If a waiver has been granted for a particular vehicle since Jan. 1, 1997, the vehicle is not eligible for another waiver. The maximum repair cost limit applies only to the cost of repairs that address the area of the failure, the amounts are as follows.

Pre-1988 Diesel Engines and Vehicle Emissions Inspections

If you've received a letter from ADEQ regarding a diesel-powered vehicle with a gross weight greater than 26,000 pounds that must meet 1988 or newer emission standards, you can click on the following to obtain a copy of the appropriate form.

• Remanufactured engine
• Replaced parts
• Retrofitted engine
• Current engine meets 1988 or newer standards
• Area A Map for Pre-88 Diesel Engines
• Arizona Tailpipe Standards (40 CFR Part 86) for Pre-88 Diesel Engines