Clean Truck Check 2027 quarterly testing and deadlines

Short answer: Most trucks covered by Clean Truck Check currently test twice a year. Under CARB's original rule, OBD-equipped vehicles move to four tests a year (quarterly testing) starting October 1, 2027. A bill has proposed cutting testing to once a year, so the schedule may change; your own deadlines are always in CARB's CTC-VIS system.

Where Clean Truck Check stands in late 2026

Clean Truck Check is CARB's heavy-duty inspection and maintenance program, often called HD I/M. It covers most diesel and alternative-fuel vehicles over 14,000 lb GVWR that operate in California, including out-of-state and international trucks.

Today, the picture for most owners is:

• Each vehicle is reported in CTC-VIS and the owner pays CARB's annual compliance fee per vehicle.
• Most covered vehicles test twice a year.
• Each vehicle has its own deadlines, shown in CTC-VIS.
• Missing a deadline can lead to a DMV registration hold for California-registered vehicles, plus CARB citations and penalties.

When is my Clean Truck Check due in 2026?

Your deadline is specific to your vehicle, and the only reliable place to see it is CTC-VIS. Log in, find the vehicle by VIN and look at the next compliance deadline.

People often ask whether the deadline is tied to the DMV registration month, and how the testing window works. CARB sets those details, and how they apply can depend on the vehicle and its registration. We don't want you to plan around a guess, so check the deadline and window shown for your vehicle in CTC-VIS, or check CARB's rules. If you want a second pair of eyes, we can help you read what CTC-VIS shows.

Clean Truck Check 2027: quarterly testing for OBD trucks

Under CARB's original rule, OBD-equipped vehicles move from twice-a-year testing to four tests a year from October 1, 2027. That affects:

• 2013 and newer diesel engines, which use the CARB-verified OBD test.
• 2018 and newer alternative-fuel engines, which also use the OBD test.

For a fleet, quarterly testing roughly doubles the number of OBD tests per truck each year. That means more scheduling, more chances to miss a deadline and more value in keeping trucks fault-free between tests.

Non-OBD vehicles (2012 and older diesels getting a smoke opacity test and visual inspection, and 2017 and older alternative-fuel engines getting a visual inspection) are not part of that OBD change. Check CTC-VIS for their schedule.

What might change: the once-a-year bill

A bill has proposed cutting Clean Truck Check testing to once a year. If it passes, the October 2027 quarterly schedule and today's twice-a-year schedule could change. Until something is final, plan on the rule as it stands and watch CARB updates and CTC-VIS.

We won't predict how it turns out. What we can say is that owners who keep testing on time under the current rule are not hurt by any change. Owners who wait for a change and miss a deadline can end up with a registration hold.

How to plan your 2026-2027 testing now

You don't need to wait for January 2027 or for the bill to settle. A few steps make the next year easier:

1. List every covered vehicle. Include out-of-state units that run in California.
2. Pull each deadline from CTC-VIS. Put them in one calendar.
3. Group trucks by deadline. One visit can cover several trucks due around the same time.
4. Pay the annual compliance fee for each vehicle. The fee is separate from the testing fee. See the compliance fee explained.
5. Keep trucks ready to pass. Fix check engine lights, readiness monitor issues and DPF faults between tests. See readiness monitors and the check engine light.
6. Set up recurring testing. If quarterly testing takes effect, a standing schedule is easier than booking truck by truck.
7. Plan for retests. A failed truck needs repair and a retest before the deadline. See what to do after a failed test.

What a missed deadline costs you

Deadlines matter more as testing gets more frequent. For California-registered vehicles, a missed Clean Truck Check deadline can lead to a DMV registration hold. CARB can also issue citations and penalties. Out-of-state and international trucks are covered too when they operate in California, so their deadlines matter just as much. If a deadline has already passed, test as soon as you can. See missed Clean Truck Check deadline and DMV registration holds.

How early can I test before my deadline?

CARB sets when a test counts toward a deadline. Check the testing window shown for your vehicle in CTC-VIS or in CARB's rules before you book far ahead. If you are close to a deadline, book now; there is little upside in waiting.

How Diesel Dynamix helps

Diesel Dynamix is an independent mobile testing service in Southern California, not CARB. As testing gets more frequent, the time lost driving trucks to a test site adds up. We test at your yard, terminal, jobsite or port, so trucks stay close to work.

• We give you the next due date after each test and can send reminders.
• Fleets get recurring visits, early-morning visits, per-truck pricing and records per VIN. See fleet testing.
• We help with CTC-VIS questions and explain results in plain English.

For background on frequency, read how often trucks need Clean Truck Check. To get on a schedule, call or text (858) 342-8328 or book a test.