Heavy Duty Diesel Inspection Program

The Diesel Inspection Program is jointly administered by:


To ensure the Roadside Enforcement Program and Periodic Inspection Program operate effectively, the Diesel I/M unit:

  • Develops and refines the procedures and standards for testing diesel vehicles
  • Collects and analyzes inspection data from the licensed inspection centers as well as the roadside teams
  • Audits the roadside teams to ensure proper operation of equipment and correct procedures
  • Coordinates with the NJ MVC on licensing procedures and enhancements to these two inspection programs.

This unit maintains its leadership role by promoting more stringent inspection requirements for heavy duty diesel vehicles. This unit continues to explore ways to enhance its program by increasing outreach, developing partnerships, and testing new equipment and concepts.

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The intent of the diesel inspection program is to identify diesel vehicles with excessive smoke emissions as these emissions are an indicator of poor vehicle maintenance and contribute to air pollution. Diesel engines emit soot, or black carbon particles, which then become airborne.

Over 100,000 vehicles that are subjected to annual inspections must pass an emission test for smoke opacity within 90 days of their annual registration.

Roadside Enforcement Program

All HDDVs, New Jersey registered or out of state, are subject to random roadside inspections. Teams of MVC inspectors and State Police monitor a network of inspection sites that cover the entire state. The inspection sites are selected to provide maximum safety for the motoring public, the truck drivers, and the inspection team. The roadside inspection utilizes the snap-acceleration test, one of three test methods adopted by DEP. Penalties, in the form of fines, are issued for exceeding the emission standards, and for failing to have the annual inspection performed.

Periodic Inspection Program

All diesel-powered vehicles 18,000 pounds or more GVWR must undergo an annual emissions inspection within 90 days after the date of initial or renewed registration.

The inspection, which utilizes one of the three test methods adopted by DEP, must be performed at a MVC licensed diesel Private Inspection Facility (PIF). A network of almost 300 diesel PIFs has been developed across the state, in all 21 counties.

Not all diesel PIFs are repair facilities. If your vehicle needs repairs or maintenance, check with your local diesel PIF to see if they provide the services you need.

Find a diesel PIF near you: New Jersey Motor Vehicle Commission

Inspections are performed at licensed diesel PIFs under our Periodic Inspection Program. The Roadside Enforcement Program fields teams of MVC inspectors and State Police. Smoking vehicles and excessive idling of diesel engines are also prohibited.

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Other Info

Test methodologies adopted by the Department of Environmental Protection include the snap-acceleration test, rolling-acceleration test, and power brake test for determination of exhaust smoke opacity from heavy-duty diesel vehicles (HDDVs). In a roadside environment the snap acceleration test is utilized. Periodic inspection of HDDVs may utilize either of the snap-acceleration, rolling-acceleration or the power brake tests.

Measurement apparatus (opacimeters) must conform to the specifications set forth by the Society of Automotive Engineers Recommended Practice J-1667.


This test can be performed on any vehicle regardless of engine speed or transmission type. Vehicles are rapidly accelerated in low gear or “Drive” – for manual or automatic transmissions respectively – to maximum governed RPM while the smoke opacity is measured.


During this test, the vehicle is held stationary with wheel chocks as the engine is rapidly accelerated – “snapped” – to maximum governed RPM with the transmission in neutral. A smoke meter is used to determine the average opacity over several accelerations.


This test is only required on vehicles with an automatic transmission AND a high-speed engine. The vehicle is held stationary with all brakes applied and the transmission placed in “Drive”. The accelerator is fully depressed and held up to ten seconds but typically about three seconds while the smoke opacity is measured.

Smoke opacity is a measurement of light extinction, or the blackness of the exhaust plume, expressed as a percentage. 100% opacity would be completely dark, and 0% would be totally transparent. The black smoke we see in diesel exhaust is composed primarily of carbon particles resulting from the combustion of diesel fuel.

The opacity limit is measured at the peak, or darkest point, of the exhaust cloud. This measurement is most commonly taken during the snap acceleration test, where the vehicle is at idle, with all brakes off, and the throttle is “punched” to the floorboard, initiating the exhaust cloud. Opacity is measured as a surrogate for particulate matter.

The table below illustrates the approximate opacity of our current emission standards.

opacity chart

HDDVs are subject to opacity standards based on the production year of the vehicles’ engine. The standards were devised to take into account the state of engine technology, and typical wear conditions. The opacity standards are:

Current Opacity Cutpoints

Heavy-duty trucks – 18,000 pounds or more
1990 and older
1991 or 1996
1997 and newer
No visible smoke >3 consecutive seconds


Commercial & School Buses – 18,000 pounds or more
1987 and older
1988 – 1993
1994 and newer
No visible smoke >3 consecutive seconds


Retrofitted* Diesel Buses – 18,000 pounds or more
1993 and older
1994 and newer
No visible smoke >3 consecutive seconds
* Equipped with post-manufacture internal and/or external emissions control technology, and/or exhaust after-treatment devices, as required under the USEPA Urban Bus Program


Opacimeters use a light beam directed at a photo-receptor cell, to measure the exhaust smoke plume. The light is either directed through the plume itself, or a sample, or “plug” of smoke is directed into a chamber through which the light beam passes. As noted above, the degree to which the beam is obscured from the receptor cell is translated into a percentage, where a value of 100% means that the light is completely blanked out.

NJDEP approves opacimeters for use by the diesel PIFs.

List of approved opacimeters

Violations for roadside inspections are placed upon owner or lessee, not the operator. Penalties are only issued at roadside inspections.

  • The fine for a first offense is $700, reducible to $150 with proof of repair.
  • For second and subsequent offenses the fine is $1300, reducible to $500 with proof of repair.
  • Failure to comply with the annual inspection requirement carries a fine of $500.

Established by Public Law 1995, Chapter 157, the rules that govern the heavy duty diesel inspection and maintenance are:
NJ Department of Environmental Protection
N.J.A.C. 7:27-14 – Control and Prohibition of Air Pollution from diesel- fueled Motor Vehicles
N.J.A.C. 7:27B-4 – Air Test Method 4: Testing procedures for Motor Vehicles
NJ Department of Transportation
N.J.A.C. 13:20-26 – Periodic Diesel Inspection Program
N.J.A.C. 13:20-46 – Diesel Emission Inspection and Maintenance Program
N.J.A.C. 13:20-47 – Diesel Private Inspection Facility – Licensing
NJ State Police
N.J.S.A. 39:8-59 – 76 – Periodic Diesel Inspection Program