Clean Truck Check, California heavy duty smog check rules

What is Clean Truck Check

Clean Truck Check is California's smog check for heavy trucks. The California Air Resources Board, or CARB, runs it. It covers nearly every diesel and alternative fuel vehicle over 14,000 pounds gross vehicle weight rating that drives on California roads. The state law behind it is SB 210, signed in 2019.

This is a different program from the regular Smog Check that the Bureau of Automotive Repair runs for cars and light trucks. If your vehicle weighs 14,000 pounds or less, read the diesel smog check guide or the regular rules instead. If it weighs more, this page is for you.

The 14,000 pound line is the key. A big pickup that sits at or under it stays in Smog Check if it is diesel and model year 1998 or newer. A box truck, tractor or bus above it is a Clean Truck Check vehicle. The rating that counts is the gross vehicle weight rating, which is the most the truck is built to carry, not its empty weight.

Which vehicles must pass Clean Truck Check

The rule reaches almost all heavy diesel and alternative fuel vehicles, no matter who owns them or where they are registered.

• Trucks and tractors of every kind over 14,000 pounds
• Buses
• Government owned vehicles
• Out of state trucks that drive on California roads
• California registered motorhomes over 14,000 pounds
• Alternative fuel engines such as natural gas

Some vehicles are left out.

• Zero emission vehicles
• Emergency vehicles
• Military tactical vehicles
• Historical vehicles
• Out of state motorhomes
• Very low nitrogen oxide engines, through 2027

DMV counted 664,319 heavy duty diesel vehicles registered in California at the end of 2024, and 26,426 heavy natural gas vehicles. DMV marks each record light or heavy but does not publish the weight line in the file. So treat those counts as a rough guide to the size of the fleet, since out of state trucks are covered too.

Clean Truck Check timeline

The program rolled out in steps. Roadside monitoring came first. Required testing came next. The big change is still ahead in October 2027.

How often you have to test

Most vehicles test twice a year. CARB calls this semi annual testing. Your deadlines are tied to your DMV registration month and to the month six months later. A truck registered in March has deadlines in March and September.

You can send in a passing test up to 90 days before the deadline. Do not wait. If a truck fails you need time to fix it and test again before the deadline passes.

Every deadline on or after January 1, 2025 needs a passing test. Motorhomes and agricultural vehicles stay on an annual schedule. Beginning in October 2027, vehicles that have OBD, which is the onboard diagnostic system, move to testing four times a year. CARB sets exact dates for your truck in its system, so check the portal for your own deadlines.

How much does Clean Truck Check cost

Each vehicle pays an annual compliance fee to CARB. It is $31.18 for 2025, $32.13 for 2026 and $33.12 for 2027. The fee is adjusted for California inflation, so it rises a little each year. The 2026 fee was up 3.0% from 2025, and the 2027 fee is up 3.1% from 2026.

That fee is separate from what a tester charges to run the test. This page has no price list for testers, so ask for a quote before you book. Fees on a fleet add up. A company with 50 trucks pays $1,606.50 in compliance fees for 2026.

Planning for a fleet

Fleet managers should count tests and not only fees. A truck that tests twice a year needs two passing results a year. After October 2027 a truck with OBD needs four. A yard with 50 OBD trucks goes from 100 tests a year to 200. The table below shows the math.

The fee is only part of the cost, since testers charge for the test and a failed truck needs repairs. Build a calendar with each truck's two deadlines. Add the test window, which opens about 90 days earlier. Then assign one person to watch the results. Because a registration hold stops a truck from renewing, one missed deadline can park a revenue truck.

• Group trucks by registration month. Trucks that renew in the same month test at the same time, so one tester visit can cover them.
• Scan before you test. A truck with a stored fault code is more likely to fail an OBD test. Fix the code first.
• Keep your passing test records where your manager can find them fast.
• Budget for the 2027 jump. The fee rises with inflation, and the test count doubles for OBD trucks.

What tests do trucks get

The test depends on the engine and its year. Newer diesels get a computer scan, and older ones get a smoke test.

An OBD scan reads the truck's own computer. It looks for stored fault codes. A smoke opacity test measures how dark the exhaust is. The tester also does a visual check for missing or changed emissions parts. Alternative fuel engines from 2017 and earlier only get the visual check.

Testers must have passed CARB's free online course with a score of 80% or better. They must renew every two years.

About 77% of the heavy diesel vehicles in DMV's file are model year 2013 or newer, so most will get the OBD scan.

The truck fleet behind the rule

DMV data gives a picture of who the rule reaches. At the end of 2024, California had 664,319 registered diesel vehicles that DMV marks as heavy. About 511,972 of them, or 77%, are model year 2013 or newer and should get the OBD scan. Another 152,347 are 2012 or older. Of those, 108,113 are model year 2010 or older, and DMV groups them in one line. Those older engines get the smoke opacity test and the visual check.

The most common model year among the heavy diesels from 2011 on is 2020, with 56,770 vehicles. The newest model year, 2025, shows only 3,229 because the DMV snapshot was taken at the end of 2024.

DMV also lists 599,938 diesel vehicles it marks light. Those that weigh 14,000 pounds or less and are model year 1998 or newer stay in the BAR Smog Check program. The light and heavy marks in the DMV file do not match the 14,000 pound line exactly, so use these as a size guide, not a headcount of who must test.

Common mix ups

• My pickup is a diesel, so I need Clean Truck Check. Not if its rating is 14,000 pounds or less. It goes to a regular smog station. Check the door sticker, because some heavy pickups sit above the line.
• My truck is registered in another state. It is still covered when it drives in California.
• My motorhome is a gas rig. The rule covers diesel and alternative fuel vehicles. Check the engine type and the weight rating.
• The regular smog check exemptions apply to trucks. They do not. The eight year and four year exemptions are for gas cars in the BAR program.
• One test a year is enough. Most vehicles need two. Motorhomes and agricultural vehicles are the annual ones.

What happens if you do not comply

CARB can ask DMV to put a hold on a truck's registration. You cannot renew while a hold is in place. CARB also sends a Notice to Submit to Testing. It gives you 30 days to test. Skip it and the registration hold becomes more likely.

• Keep your passing test record. It is your proof.
• Test early. The 90 day window is there so you can fix problems.
• If a truck fails, fix the fault and test again before your deadline.
• Call the Clean Truck Check hotline at (866) 634-3735 if you get a notice you do not understand.

Roadside emissions monitoring began in January 2023, so CARB can watch trucks on the road, not only at your yard.

Out of state trucks and motorhomes

Out of state trucks are covered if they drive on California roads. You do not escape the rule by registering in another state. The one exception is the out of state motorhome, which is not covered. California registered motorhomes over 14,000 pounds are covered and test once a year.

If you drive a big motorhome and you are not sure of its weight rating, read the sticker on the door frame. If it is 14,000 pounds or less and it runs on diesel, the regular smog check may apply instead, as long as it is model year 1998 or newer.

Step by step to comply

1. Check the weight. Find the gross vehicle weight rating on the door sticker. Over 14,000 pounds means Clean Truck Check.
2. Register your vehicles. Many owners look for the Clean Truck Check login. Start at the CARB program page in the sources below and follow its links.
3. Find your deadlines. They follow your DMV registration month and the month six months later.
4. Pay the annual compliance fee for the year.
5. Book a credentialed tester within 90 days before the deadline.
6. Fix any failure and retest.
7. Keep your proof and watch for the October 2027 change to four tests a year.

Own a pickup or a van and not a big rig? Go to the smog station finder to find a regular smog check station. If you are curious how the state compares, see California smog check by the numbers.