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Current Opacity Inspection Programs

In 2019, changes were made to the Periodic Smoke Inspection Program (PSIP) and the Heavy-Duty Vehicle Inspection Program (HDVIP). The California Air Resources Board approved a new opacity limit of 5 percent for heavy-duty vehicles equipped with diesel particulate filters (DPFs). Other amendments include additional smoke tester training requirements and voluntary submittal of on-board diagnostic (OBD) data in lieu of annual PSIP opacity tests.

The PSIP is an annual self-testing program for smoke opacity and is applicable to California-based fleets of two or more heavy-duty diesel vehicles. HDVIP is a roadside inspection program conducted by the California Air Resources Board (CARB) enforcement staff and is applicable to diesel and gasoline heavy-duty (HD) vehicles operating in California over 6,000 pounds gross vehicle weight rating (GVWR).

The following frequently asked questions (FAQs) provide basic information related to CARB’s regulatory revisions to the PSIP and HDVIP to reduce the opacity threshold. For additional information, please see the offical CARB webpage.

Opacity Standards - PSIP Advisory 298

SMOKE TESTING COMPLIANCE ADVISORY – CALIFORNIA’S PERIODIC SMOKE INSPECTION PROGRAM (PSIP) FOR HEAVY-DUTY DIESEL VEHICLES (HDDVs) - This regulatory advisory is to help inform the end user on the proper reading and interpretation of opacity test results using currently available smoke meters for HDDVs.

What are California’s heavy-duty vehicle inspection programs?

CARB’s Periodic Smoke Inspection Program (PSIP) and Heavy-Duty Vehicle Inspection Program (HVDIP) were adopted to control excessive smoke emissions and tampering from heavy-duty diesel trucks and buses. The regulations, title 13 CCR, sections 2190-2194 for PSIP and title 13 CCR, sections 2180-2189 for HDVIP, govern these programs.

How do the PSIP and HDVIP programs work?

Periodic Smoke Inspection Program (PSIP)

PSIP is an annual self-testing program for smoke opacity and is applicable to California-based fleets of two or more heavy-duty diesel vehicles over 6,000 pounds GVWR with engines over four years old (note: 1998 and newer diesel vehicles subject to biennial smog check with a GVWR between 6,000 and 14,000 pounds are not subject to PSIP).  The PSIP program requires that fleet owners conduct annual smoke opacity inspections of their HD diesel vehicles and repair those with excessive smoke emissions to ensure compliance.  All vehicles that do not pass the test must be repaired and retested.  All testing records must be maintained for a period of two years.  CARB audits fleet maintenance and inspection records and tests a representative sample of vehicles.  A fleet owner that neglects to perform the requirements of the PSIP regulation is subject to penalties.

Heavy-Duty Vehicle Inspection Program (HDVIP)

All heavy-duty trucks and buses over 6,000 pounds GVWR operating in California are subject to HDVIP roadside inspections by CARB staff.  This includes vehicles registered in other states or foreign countries.  CARB inspectors may conduct unannounced tests at border crossings, CHP weigh stations, fleet facilities, and other selected roadside locations.  Vehicles are inspected for excessive smoke and tampering, and engine certification label compliance.  Owners of trucks and buses found in violation are subject to minimum penalties starting at $300 per violation.

What are the program requirements?

The table below depicts the opacity limits for the PSIP & HDVIP programs.     

Engines Equipped with a DPF

5% Opacity Limit

Pre-2007 Model Year (MY) Engines not Equipped with a DPF

1997-2006 MY Engines

20% Opacity Limit

1991-1996 MY Engines

30% Opacity Limit

Pre-1991 MY Engines

40% Opacity Limit

Engines Equipped with a Level 2 Verified Diesel Emission Control Device

20% Opacity Limit

Two Engine Cranes Driven by a non-DPF Off-Road Engine

40% Opacity Limit

-For OBD-equipped engines (2013 Model Year and Newer), fleets can choose to submit a vehicle’s OBD data to CARB in lieu of performing annual opacity tests.  OBD-equipped engines with PM related fault codes will need to undergo repairs to clear the codes.

-Training is required to conduct opacity tests. Commercial smoke testers conducting smoke tests for a fee must complete the California Council on Diesel Education Technology (CCDET) in-person training course, also known as CCDET I, or another CARB approved in-person smoke tester course. Fleet employees testing their own company vehicles can also fulfill the training requirement by completing the CARB online training course available at the Learning Management System, see course MS529 – Online Smoke-Test Training.

To become a CARB-approved provider of an in-person training course for commercial smoke test providers, see PSIP Advisory 294.

Is this part of longer-term development of a Heavy-Duty Inspection and Maintenance Program?

Yes, the California Air Resources board has adopted the Heavy-Duty Inspection & Maintenance program (HD I&M) and will be effective soon. View more information on the HD I&M TruckStop page.

Where do I get additional Information?

Visit the Smoke Inspection Programs page for information on development of regulation.

If you have questions regarding PSIP and HDVIP implementation, please contact If you have questions regarding development of a longer term comprehensive Heavy-Duty Inspection and Maintenance Program, please contact Krista Fregoso at (916) 445-5035 or at

Visit for information on preventive maintenance techniques and smoke test training.

How can I receive information on future regulatory developments?

To receive information on the implementation of the Heavy-Duty Inspection and Maintenance Program, sign up on the GovDelivery list (check the Heavy-Duty Vehicle Inspection and Maintenance box).