How often do trucks need Clean Truck Check?

Clean Truck Check frequency in 2026 and 2027

Most covered trucks test twice a year in 2026. Under CARB's original rule, that changes for OBD-equipped trucks on October 1, 2027.

Now (2026):

• Most covered vehicles: two tests a year, which works out to roughly one every six months.
• This applies to OBD trucks and to older diesels that take the smoke opacity test.

From October 1, 2027 (original rule):

• OBD-equipped vehicles: four tests a year.
• The quarterly change applies to OBD trucks. Non-OBD trucks that take the smoke opacity test are not part of that change under the original rule.

What could change: a bill has proposed cutting Clean Truck Check to once a year. Until a change is final, plan for the current schedule.

How often semi trucks need emissions testing in California is the same answer as any other covered truck: it depends on the engine type and CARB's current rule. Your own due dates are always in CTC-VIS.

Building a Clean Truck Check schedule by truck

Each truck has its own due dates, so the schedule has to be by truck, not by fleet. Two trucks in the same yard can be due months apart.

A simple way to set it up:

1. Pull every truck's deadline from CTC-VIS.
2. Make one list by VIN with the test type (OBD or smoke) and next due date.
3. Group trucks with nearby deadlines so one visit covers several.
4. Leave time for a retest in case a truck fails and needs a repair.

When quarterly testing starts for OBD trucks, the same list keeps working. It just has more dates on it.

Diesel Dynamix does this tracking for you. After each test we give you the truck's next due date, keep the record by VIN, send reminders and can set up recurring visits to your yard. See fleet testing or call (858) 342-8328.