Most diesel trucks in California need an emissions inspection, and which program applies comes down to weight. Diesel trucks with a gross vehicle weight rating of 14,000 pounds or less go through the state’s biennial Smog Check program. Trucks over 14,000 pounds GVWR fall under the California Air Resources Board’s Clean Truck Check program instead. The California diesel truck smog check requirements are different enough between those two categories that treating them as one system leads to expensive mistakes.
Light-Duty Diesel Trucks
Since 2010, diesel trucks with a GVWR under 14,001 pounds and a model year of 1998 or newer have been part of California’s standard Smog Check program.1Bureau of Automotive Repair. New Diesel Smog Check Requirements Coming Soon That covers most diesel pickups and SUVs on the road today. Model year 1997 or older diesels are exempt from the Smog Check program entirely.2Bureau of Automotive Repair. Smog Check: When You Need One and What’s Required
A Smog Check is required every other year at registration renewal, and also when the vehicle is sold or transferred.2Bureau of Automotive Repair. Smog Check: When You Need One and What’s Required Two age exemptions that apply to gasoline vehicles do not apply to diesels. Gasoline vehicles less than eight model years old skip the biennial Smog Check; diesels do not.3Bureau of Automotive Repair. Smog Check Reference Guide 2025 Gasoline vehicles under four model years old skip the smog inspection on a change of ownership; diesels do not get that pass either.4California DMV. Smog Inspections A brand-new diesel truck needs a Smog Check at its first biennial renewal.
The inspection itself includes a visual check of the emissions control system, a functional check, and an on-board diagnostics (OBD II) scan to confirm required readiness monitors have run.1Bureau of Automotive Repair. New Diesel Smog Check Requirements Coming Soon Pre-2000 diesels may also undergo a tailpipe emissions test. There is no dynamometer portion for diesel vehicles. A passing certificate is sent electronically to the DMV and stays valid for 90 days.2Bureau of Automotive Repair. Smog Check: When You Need One and What’s Required
Registering a diesel as a collector car does not create an exemption. The Bureau of Automotive Repair specifies that collector cars meeting the standard criteria still need a Smog Check, so a 1998 or newer diesel truck needs one regardless of collector status.2Bureau of Automotive Repair. Smog Check: When You Need One and What’s Required
Heavy-Duty Diesel Trucks
Diesel trucks over 14,000 pounds GVWR are exempt from the regular Smog Check because they are regulated separately under CARB’s Clean Truck Check.5California Air Resources Board. Clean Truck Check – Overview Fact Sheet CARB launched the program with roadside emissions monitoring in January 2023, and mandatory emissions compliance testing took effect on October 1, 2024.6California Air Resources Board. Clean Truck Check-Vehicle Inspection System (CTC-VIS) Online User Guide
The cadence is much tighter than the biennial Smog Check. Almost all heavy-duty vehicles must demonstrate compliance every six months. Agricultural vehicles and non-commercial motorhomes stay on an annual schedule. Passing test results can be submitted up to 90 days before a compliance deadline.7California Air Resources Board. Clean Truck Check – Emissions Compliance Testing Requirements
Which test applies depends on the engine. Trucks with 2013 or newer diesel engines get an OBD-based scan. Trucks with pre-2013 diesel engines get a SAE J1667 smoke opacity test along with a visual and functional inspection of emissions control equipment.8California Air Resources Board. Clean Truck Check (HD I/M) The opacity test measures exhaust smoke during a snap-acceleration procedure. All compliance testing must be performed by a CARB-credentialed tester.5California Air Resources Board. Clean Truck Check – Overview Fact Sheet
Clean Truck Check also applies to heavy-duty diesel trucks operating on California roads even when they are registered in another state.5California Air Resources Board. Clean Truck Check – Overview Fact Sheet Interstate operators need the vehicle reported in the CTC Vehicle Inspection System, the annual compliance fee paid, and a passing emissions test on file before driving on California public roads.9California Air Resources Board. Clean Truck Check Requirements for Vehicles Subject to Semi-Annual Compliance Compliance deadlines for non-California-registered vehicles are set by the last digit of the VIN and recur every six months.
Note that a separate program, the Truck and Bus Regulation, requires older heavy-duty diesels to be replaced or repowered with a 2010 or newer engine.10California Air Resources Board. Truck and Bus Regulation Requirements A heavy-duty truck has to comply with both this rule and Clean Truck Check to operate legally.
Exemptions
- Light-duty diesel trucks model year 1997 and older are exempt from the Smog Check program.2Bureau of Automotive Repair. Smog Check: When You Need One and What’s Required
- Under the Truck and Bus Regulation, heavy-duty vehicles operating less than 1,000 miles per calendar year in California can qualify for a low-use exemption from that regulation’s engine upgrade requirements. Vehicles using stationary power take-off equipment must also run the engine less than 100 hours per year.11California Air Resources Board. Truck and Bus Regulation Low-Use Vehicle Exemption FAQ
- Authorized emergency vehicles are exempt from Clean Truck Check if they meet the definition under California Vehicle Code 165 or Health and Safety Code 1797.84. Government ownership alone does not qualify a vehicle; it has to meet the authorized emergency vehicle definition specifically.12California Air Resources Board. Clean Truck Check – Authorized Emergency Vehicles and Out of State Vehicles Operating Under Emergency Declaration/EO
- During the first four years of CTC implementation (2023 to 2027), new heavy-duty vehicles with engines certified to the most stringent optional NOx standard are temporarily exempt from compliance testing.5California Air Resources Board. Clean Truck Check – Overview Fact Sheet
What It Costs
For heavy-duty trucks in Clean Truck Check, CARB charges an annual compliance fee of $32.13 per vehicle as of January 1, 2026, up from $31.18 the prior year.13California Air Resources Board. Clean Truck Check Compliance Fee Update Effective 1/1/2026 That covers the regulatory side only. The testing itself, performed by a CARB-credentialed tester, is a separate cost that varies by provider.
For a light-duty diesel Smog Check, you pay the station’s inspection fee plus a state certificate fee if the vehicle passes. Average inspection costs at California stations run roughly $58 to $73 depending on station type, though diesel inspections may run higher. The state does not cap inspection prices, but stations cannot enter inspection costs exceeding $99 into the BAR system.
What Happens If You Don’t Comply
For heavy-duty trucks, CARB uses roadside emissions monitoring devices and automated license plate readers to screen for high emitters. Flagged vehicles receive a Notice to Submit to Testing from CARB Enforcement, and CARB and the California Highway Patrol also run field inspections at weigh stations.8California Air Resources Board. Clean Truck Check (HD I/M)
The DMV automatically places registration holds on trucks that are not compliant with Clean Truck Check. A hold under SB 210 blocks most DMV transactions, including registration renewal.14California Air Resources Board. Clean Truck Check – CA DMV Registration Hold (SB 210) To clear it, you have to report the vehicle in CTC-VIS, pay the annual fee, and submit a passing test. The hold lifts one to three business days after that, but the DMV will not automatically send registration tags. You need to contact them to finish the transaction. Non-compliant trucks can also be turned away at ports and railyards, which shuts down commercial operations.
For light-duty diesel trucks, a failed Smog Check means you cannot renew your registration until the vehicle passes.
Repair Help for a Failed Smog Check
If your light-duty diesel truck fails its Smog Check and you meet income limits, the Bureau of Automotive Repair’s Consumer Assistance Program may help cover repairs. Vehicles model year 1996 or newer can qualify for up to $1,450 toward emissions-related repairs, and model years 1976 through 1995 can qualify for up to $1,100.15Bureau of Automotive Repair. Apply for Repair Assistance
To qualify, your gross household income must be at or below 225% of the federal poverty level, you must be the registered owner with the title in your name, and the vehicle must have failed its biennial inspection without any tampered emissions equipment. Registration must be current or expired no more than 365 days ago. Vehicles registered to businesses, government agencies, or nonprofits are not eligible, and the program does not cover vehicles undergoing initial registration or ownership transfers.