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Changes Are In the Air: New CARB Inspection and Maintenance Requirements Take Aim at Heavy Duty Diesel Emissions

The role of the California Air Resources Board (CARB) is to implement effective solutions to curb air pollution in our state. In 2006, they additionally became the steward of the world’s first comprehensive programs to regulate mechanisms to achieve greenhouse gas reductions. CARB is in the driver’s seat on researching, monitoring, and adopting standards to thwart the effects of climate change, and to this end, they are stepping up their game.

To ensure the emissions control systems of heavy duty diesel vehicles maintain efficiency and continue to operate properly as they age, CARB is introducing a new program: The Heavy-Duty Inspection Maintenance Regulation (HD I/M). By monitoring, if factory-installed emissions control systems are working properly while minimizing inspection downtime for vehicle owners, CARB intends to reduce the NOx and fine particle diesel pollution by 82 tons per day by 2037.

Fleet owners and owner/operators of heavy-duty diesel equipment: Learn about the HD I/M Regulation now or be left in the dust. Consequences for non-compliance include a violation citation that comes with a financial penalty, plus a DMV block on your vehicle’s registration. 

The Nuts and Bolts of the CARB Heavy Duty Inspection & Maintenance Program

In 2019, Senate Bill 210 paved the way for CARB’s HD I/M program to deal with updating the periodic smoke inspection program. Their goal is to make this program more like a smog inspection program that works with partner state agencies—the DMV, CHP, and the BAR (Bureau of Automotive Repair)—for monitoring and enforcement.

In December 2021, CARB approved the HD I/M Regulation for adoption to:

• Target malfunctioning vehicles with high emissions
• Require all vehicles in the state of California to comply
• Utilize the tech of on-board diagnostic (OBD) telematics systems to identify faulty emissions-related components
• Conduct smog checks for heavy-duty diesel trucks

Do You Need to Comply, or Are Your Vehicles Exempt?

The HD I/M Regulation applies to both owners and operators of:

• Non-gasoline, diesel, and alternative fuel vehicles registered in California with a gross vehicle weight rating (GVWR) of more than 14,000 lbs.
• Vehicles of non-California registered vehicles operating in the state with a GVWR of more than 14,000 lbs.

Unlike the existing Smoke Inspection Program, there are limited exemptions for:

• Zero emission trucks
• Emergency vehicles
• Military tactical vehicles
• The newest HD vehicles with engines certified by the most recent NOx standards
• Historical vehicles
• Motorhomes with out-of-state registrations


• Gasoline heavy-duty vehicles that have a GVWR of more than 14,000 lbs. (These vehicles must continue to be compliant with the BAR’s Smog Check Program)

Keep in Mind: All previous CARB emissions requirements remain in force as the new requirements are phased in. To find out whether you are up-to-date on the present Truck and Bus Rules set forth by the California Air Resources Board, contact our in-house emissions consultants.  

The HD I/M Regulation Rollout Timeline

Effective January 1, 2023, high-emitter vehicle screening and follow-up compliance testing begins. To be compliant:
• You must have no outstanding enforcement actions against your vehicle
• You must have no outstanding emissions or OBD-related recalls on your vehicle (OBD are the on-board diagnostics, the computer system that runs the engine and monitors all the emissions-related components on the engine)

Effective no earlier than July 1, 2023, to be compliant:
• The annual compliance fee is due to CARB
• Your owner and vehicle information is reported to CARB’s HD I/M database
• Freight contractor and facility verification begins

Effective no earlier than January 1, 2024, the full HD I/M program is implemented. To be compliant:
• You must submit a passing Periodic Vehicle Emission Compliance Test to CARB

How Are Vehicles Monitored?

Roadside emissions monitoring devices (REMDs) are the timesaving method this new program employs to keep you on the road. Along with roadside cameras, REMDs will assist in taking an instantaneous reading of the emissions coming from vehicles passing them and will capture info about the vehicle itself and the ownership of the vehicle. Imagine license plate cameras that can additionally take emissions readings and you have a picture of the future of vehicle pollution monitoring.

This REMD network will phase in throughout California in January of 2023, identifying potential high-emitting vehicles for follow-up compliance testing. You’re likely to see these emission-reading devices at weigh stations and at random roadside areas, such as onramps—Wherever there is the potential for high-emitting vehicles to pass through.

If your vehicle is flagged as a potential high emitter, you’ll receive a notice to submit to testing (NSA). This isn’t a citation—Just a notice that requires that you must have your vehicle pass a compliance test within 30 days.

Even if your vehicle is not flagged as a potential high emitter, you will need to submit your vehicle to periodic vehicle testing on emissions-related components:

For 2013 and newer model year engines and 2018 and newer model year engines for alternative fuel OBD-equipped vehicles:

• OBD test submission 2x/year. This increases to 4x/year three years after the start of periodic inspections
• CA motorhomes and on-road ag vehicles: 1x/year

For Pre-2013 model year engines: non-OBD-equipped vehicles:

• Smoke opacity test from the Periodic Smoke Inspection Program (a device that reads the amount of smoke coming from the stack) and visual/functional emissions control component inspection will need to occur 2x/year
• On–road ag vehicles and California motorhomes will need to pass the smoke opacity test and a visual/functional emissions control component inspection 1x/year

How compliance deadlines are determined:

For CA-registered vehicles: your DMV registration date will determine when you’ll need to perform this test. Whatever your registration date is, you’ll have a 90-day window to submit a passing test. Six months from that registration date is when the second test will need to be performed and submitted, again, with a 90-day window to complete the second test.
For out-of-state registered vehicles: The month that the last number of VIN number corresponds to is when the data initially needs to be submitted within a 90-day window. Six months from that date, the second test would need to be submitted within 90 days from that date.

How Are Vehicles Tested?

Testing is easy when you have a telematics system that meets CARB’s data format requirements for the OBD data scan. These telecommunication devices can transmit info about your emission-related components to the REMD system. You wouldn’t need to worry about taking your vehicles offline to submit to tests because these devices allow the testing to happen automatically!

For non-OBD vehicles, a smoke opacity test using SAE J1667 specifications for diesel vehicles, along with a vehicle emissions control equipment inspection (the visual/functional test performed on all non-OBD vehicles), are required. A CARB-approved HD tester must perform all testing.

How to Prepare for the HD I/M Testing

Don’t let these upcoming changes from the California Air Resources Board catch you off guard. Learn which devices fit your OBD fleet, and learn how your non-OBD vehicles can be compliant with CARB from the CARB emissions experts at Advanced Emission. Reach out to our emissions consultants at (559) 240-6076 for a comprehensive CARB analysis, and be code compliant for the long haul. Bookmark this page and check back here on the blog to stay tuned for future updates. 

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