In 2026, most heavy-duty trucks need Clean Truck Check testing twice a year (semi-annual). Starting October 2027, OBD-equipped trucks — generally 2013+ diesel and 2018+ alternative fuel — move to four times a year (quarterly). Non-OBD vehicles and agricultural vehicles stay on their current schedule.
If you run heavy-duty trucks in California, the testing rules have been a moving target since the program started — and they're about to change again. Here's exactly how often you need to test right now, what's coming, and how to stop it from eating your time.
What is Clean Truck Check?
Clean Truck Check — officially the Heavy-Duty Inspection and Maintenance (HD I/M) program — is California's emissions testing requirement for heavy-duty vehicles. It applies to most trucks over 14,000 pounds GVWR operating on California roads, whether they're registered in California or out of state. The program requires periodic emissions testing, an annual compliance fee, and reporting to CARB's CTC-VIS system.
The part that trips people up is the periodic testing — because how often you test has been increasing over time, and it's not the same for every truck.
How often do you test in 2026?
For 2026, the requirement for most non-agricultural heavy-duty vehicles is semi-annual testing — twice per year. Your two deadlines are set by your California registration renewal date, or, for out-of-state and DMV-exempt vehicles, by the last digit of your VIN. The second test each year is due about six months after the first.
One detail worth knowing: you can submit a passing test up to 90 days before your deadline. That early window matters, because it gives you time to fix and retest if a truck fails. Don't test earlier than 90 days out, though — a test submitted outside the applicable compliance window may not satisfy the upcoming testing requirement.
| Vehicle type | 2026 frequency |
|---|---|
| Most non-agricultural heavy-duty trucks | Twice a year (semi-annual) |
| OBD vehicles (2013+ diesel, 2018+ alt-fuel) | Twice a year — until Oct 2027 |
| Older diesel (2012 & older, smoke-tested) | Twice a year |
| Agricultural vehicles & some motorhomes | Annual (once a year) |
The big change: quarterly testing in October 2027
Here's the part most fleet owners haven't caught yet. Beginning October 2027, OBD-equipped vehicles move from twice a year to four times a year. That's the newer trucks — generally 2013-and-newer diesel and 2018-and-newer alternative fuel engines with an OBD connection.
To be precise, because the exact date matters: CARB's own guidance states the quarterly requirement begins October 2027, and it applies specifically to OBD vehicles. Older smoke-and-visual (opacity) tested trucks are not moving to quarterly — they stay on their existing schedule. Agricultural vehicles and qualifying motorhomes remain on an annual schedule.
So if your fleet is mostly newer diesels, your testing workload is about to double — from two events a year per truck to four. For a 10-truck fleet, that's the difference between 20 testing events a year and 40.
Which test does your truck need?
Two different tests, depending on the engine:
OBD test — for 2013-and-newer diesel and 2018-and-newer alternative-fuel engines. A certified device scans the engine's onboard diagnostics and submits the result to CARB. This is the group moving to quarterly in October 2027, and the group the CC40 can automate.
Smoke and visual (OVI) test — for 2012-and-older diesel engines. This is a smoke opacity test plus a visual inspection of the emissions equipment, performed by a credentialed tester. It can't be automated by a device — it needs a person.
Many fleets are mixed, which means both tests apply across the yard. You can have one truck on the OBD/quarterly path and the one parked next to it on the older semi-annual smoke test.
What happens if you miss a deadline?
This is where it gets expensive. CARB tracks compliance in its database, and your test status is visible to enforcement and the DMV. Miss a deadline and you can face a DMV registration hold — which stops you from renewing plates and can take the truck off the road entirely — along with fines and civil penalties. There's no informal grace period; the system runs on submitted results and dates.
The more often you have to test, the more chances there are to miss one. Which is exactly why the 2027 quarterly change matters more than it first sounds.
How to make testing frequency a non-issue
There are two honest ways to handle a rising testing schedule.
Keep scheduling it manually. Track every truck's deadlines, book a tester or a shop each cycle, and pull trucks off the road for it. This works — it's just more work every year as the frequency climbs, and every missed date is a registration risk.
Automate the OBD trucks. For OBD-eligible vehicles, an automatic testing device like the CC40 handles the testing on its own. It stays plugged into the truck, runs the test when the vehicle is ready, and submits it to CARB over its own cellular connection. Whether the requirement is twice a year or four times a year, the device just does it — the workload doesn't change for you.
That's the real point of automating: for fleet staff, quarterly testing creates far less recurring scheduling work when eligible OBD testing is automated. Four cycles or two, you're not scheduling, not booking, not pulling trucks off the road. For the older trucks that still need a smoke test, mobile testing comes to your yard so you're not driving those anywhere either.
Tell us what you're running and we'll tell you which trucks are OBD, which need smoke testing, when each one is due, and what's changing for you in 2027. One call, no obligation.
Frequently asked questions
How often is Clean Truck Check testing in 2026?
When does quarterly testing start?
Does quarterly testing apply to all my trucks?
Can I test early?
Can a device handle the testing automatically?
Sources: California Air Resources Board, Clean Truck Check / HD I/M program guidance. Deadlines and requirements are set by CARB and subject to change — verify your vehicle's status in CTC-VIS.