Yes, almost every diesel truck registered in California needs an emissions inspection, but which program applies depends on the truck’s weight. California diesel truck smog check requirements split at a gross vehicle weight rating of 14,000 pounds. Light-duty diesel pickups and SUVs at or below that weight go through the Bureau of Automotive Repair’s biennial Smog Check program. Heavier diesels fall under the California Air Resources Board’s Clean Truck Check program, which runs on its own schedule and has its own fees.
Light-Duty Diesel Pickups and SUVs
Since 2010, diesel vehicles with a GVWR under 14,001 pounds and a model year of 1998 or newer have been part of the standard Smog Check program.1Bureau of Automotive Repair. New Diesel Smog Check Requirements Coming Soon That covers the vast majority of diesel pickups on California roads. Model year 1997 and older diesels are exempt from the program entirely.2Bureau of Automotive Repair. Smog Check: When You Need One and What’s Required
If your truck is in the program, you need a passing Smog Check every other year at registration renewal, and again whenever you sell or transfer ownership.2Bureau of Automotive Repair. Smog Check: When You Need One and What’s Required A passing certificate transmits electronically to the DMV and stays valid for 90 days.
Two exemptions that gasoline owners rely on do not apply to diesels, and this is where people get caught. 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 A brand-new diesel pickup is due for inspection at its first biennial renewal. Gasoline vehicles under four model years old also skip the smog step on a change of ownership; a diesel in the same situation does not get that pass.4California DMV. Smog Inspections
What the Light-Duty Inspection Involves
For a diesel in the Smog Check program, the inspection has three parts: a visual check of the emissions control system, a functional check, and an on-board diagnostics (OBD II) scan to confirm the required readiness monitors have run and are set.1Bureau of Automotive Repair. New Diesel Smog Check Requirements Coming Soon Pre-2000 model year diesels may also get a tailpipe test.2Bureau of Automotive Repair. Smog Check: When You Need One and What’s Required There is no dynamometer portion for diesel vehicles.
Heavy-Duty Diesel Trucks Over 14,000 Pounds
Diesel trucks with a GVWR above 14,000 pounds are not inspected under Smog Check. They fall under CARB’s Clean Truck Check program, which started roadside monitoring in January 2023 and began mandatory compliance testing on October 1, 2024.5California Air Resources Board. Clean Truck Check-Vehicle Inspection System (CTC-VIS) Online User Guide
The schedule is far more frequent than Smog Check. Almost all heavy-duty vehicles have semi-annual compliance deadlines, so a passing emissions test is required every six months.6California Air Resources Board. Clean Truck Check – Emissions Compliance Testing Requirements Starting in October 2027, OBD-equipped vehicles move to four tests per year. Agricultural vehicles and non-commercial motorhomes stay on an annual cycle. Owners can submit a passing test up to 90 days before a deadline.
The test itself depends on the engine. Trucks with 2013 or newer diesel engines get an OBD scan. Pre-2013 diesel engines get a SAE J1667 smoke opacity test under snap acceleration, along with a visual and functional inspection of the emissions equipment.7California Air Resources Board. Clean Truck Check (HD I/M) All testing must be done by a CARB-credentialed tester.8California Air Resources Board. Clean Truck Check – Overview Fact Sheet
Vehicles that operate under 1,000 miles per calendar year in California may qualify for a low-use exemption; vehicles with stationary PTO equipment must also run the engine under 100 hours per year to qualify.9California Air Resources Board. Truck and Bus Regulation Low-Use Vehicle Exemption FAQ New vehicles with engines certified to the most stringent optional NOx standard are temporarily exempt from compliance testing during the 2023–2027 implementation window.8California Air Resources Board. Clean Truck Check – Overview Fact Sheet
Out-of-State Heavy-Duty Trucks
Clean Truck Check applies to any heavy-duty diesel vehicle operating on California public roads, not just those registered in the state.8California Air Resources Board. Clean Truck Check – Overview Fact Sheet Before driving an out-of-state truck over 14,000 pounds GVWR into California, the vehicle must be reported in the CTC Vehicle Inspection System, the annual compliance fee must be paid, and a passing emissions test must be on file.10California Air Resources Board. Clean Truck Check Requirements for Vehicles Subject to Semi-Annual Compliance Compliance deadlines for non-California-registered vehicles are set from the last digit of the VIN and recur every six months.
What the Inspections Cost
Clean Truck Check carries an annual compliance fee of $32.13 per vehicle as of January 1, 2026, up from $31.18 the year before.11California Air Resources Board. Clean Truck Check Compliance Fee Update Effective 1/1/2026 That is the regulatory fee only. The emissions test itself is billed separately by the credentialed tester and varies by provider.
For a light-duty diesel Smog Check, you pay the station’s inspection fee plus a state certificate fee if the truck passes. Typical station prices run roughly $58 to $73, with diesel inspections sometimes higher. California does not cap inspection prices, though stations cannot enter inspection costs above $99 into the BAR system.
What Happens If You Skip or Fail
For a light-duty diesel, a failed Smog Check blocks registration renewal until the truck passes. There is nothing further to do once it passes: the certificate goes to the DMV electronically.2Bureau of Automotive Repair. Smog Check: When You Need One and What’s Required
For heavy-duty trucks, the consequences stack. CARB screens vehicles with roadside emissions monitors and automated license plate readers, and flagged trucks receive a Notice to Submit to Testing. CARB and the California Highway Patrol can also inspect trucks at weigh stations.7California Air Resources Board. Clean Truck Check (HD I/M) The DMV automatically places a registration hold on non-compliant vehicles under SB 210, which blocks renewal and most other transactions.12California Air Resources Board. Clean Truck Check – CA DMV Registration Hold (SB 210) Clearing the hold requires reporting the vehicle in CTC-VIS, paying the annual fee, and submitting a passing test. The hold lifts one to three business days after compliance is shown, but the DMV will not send registration tags automatically; you have to contact them to finish the transaction. Non-compliant trucks can also be refused entry to ports and railyards, which effectively parks a commercial vehicle.
Help With Repairs for a Failed Light-Duty Smog Check
If your light-duty diesel truck fails its biennial Smog Check and your household income is at or below 225% of the federal poverty level, the Bureau of Automotive Repair’s Consumer Assistance Program can help cover emissions-related repairs. Vehicles from model year 1996 or newer can qualify for up to $1,450; model years 1976 through 1995 can qualify for up to $1,100.13Bureau of Automotive Repair. Apply for Repair Assistance
To qualify, you must be the registered owner with the title in your name, and the vehicle must have failed its biennial inspection without tampered emissions equipment. Registration must be current or have 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 going through initial registration or ownership transfer.