What the California Clean Truck Check program asks of you
The California Clean Truck Check program requires most diesel and alternative-fuel vehicles over 14,000 lb GVWR to report to CARB and pass periodic emissions tests. Its formal name is the Heavy-Duty Inspection and Maintenance program. You may see it called the HD I/M program in California, or CARB HD I/M, but most drivers just call it Clean Truck Check.
For an owner, CARB Clean Truck Check comes down to three jobs:
- Report each vehicle in CARB's CTC-VIS system and pay the annual compliance fee shown there.
- Pass each Clean Truck Check test by your deadline. Most covered vehicles currently test twice a year.
- If a truck fails, get it repaired and pass a retest.
The rules cover California-registered trucks and also out-of-state and international trucks that operate in California. Buses, refuse trucks, construction and agricultural vehicles and motorhomes over 14,000 lb can be included too, so check CARB's rules for your vehicle if you are unsure.
The Clean Truck Check requirements page walks through each step in more detail, and our FAQ answers the do-I-need-it questions.
Truck smog check or Clean Truck Check? Same need, different program
If you are searching for a truck smog check in California, the test you most likely need is Clean Truck Check. Drivers still say semi truck smog check, big rig smog check or heavy duty smog check, but for vehicles over 14,000 lb GVWR the emissions testing is run by CARB under Clean Truck Check.
Which test your truck gets depends on the engine:
- 2013 and newer diesel and 2018 and newer alternative-fuel engines get a CARB-verified OBD test.
- 2012 and older diesel without OBD gets a smoke opacity test plus a visual inspection.
- 2017 and older alternative-fuel without OBD gets a visual inspection.
So a diesel truck smog check in California, or a semi truck smog check in California, for a newer tractor usually means plugging in to read the engine's own emissions data, while an older dump truck gets a smoke test. Either way, it is a commercial truck smog test with its own rules and its own reporting in CTC-VIS. For a side-by-side look, read Clean Truck Check vs. smog check.
Clean Truck Check service that comes to your trucks
Diesel Dynamix is a mobile Clean Truck Check company offering Clean Truck Check in Southern California only. Our testers drive to your yard, jobsite, terminal, port or home, so your trucks never leave to find a test site.
That matters most for carb truck emissions testing on a working fleet. A truck that sits for a test still earns money. A truck that drives across town to one does not. We schedule around your routes, offer early-morning visits and can test many trucks in one stop.
We cover Los Angeles, Long Beach, Orange County, the Inland Empire, San Diego and El Centro, plus the Ports of Los Angeles and Long Beach. See every city on our service areas page.
After the test we explain the result in plain English, give you the next due date and can send reminders before it comes around. If a truck does not pass, we tell you why so your mechanic knows where to look. We do not do repairs, and we never help with deleted or tampered equipment.
Diesel Dynamix is an independent testing service, not CARB or a government agency.
Keeping up with California truck emissions compliance
California truck emissions compliance is ongoing, not a one-time box to check. Each covered vehicle has a deadline in CTC-VIS, a yearly compliance fee owed to CARB, and a test to pass on schedule.
Missing it has real costs. California-registered vehicles can get a DMV registration hold, and CARB can issue citations and penalties to trucks that operate in the state without being compliant.
The schedule may also change. Most covered vehicles test twice a year today. Under CARB's original rule, OBD-equipped vehicles move to four tests per year from October 1, 2027, though a bill has proposed cutting testing to once a year. Keep an eye on 2026 and 2027 deadlines.
We help make CARB compliance for trucks in California simple:
- Answers to your CTC-VIS questions
- Records kept per truck and VIN
- Reminders before each due date
- Recurring visits for fleets
Call or text (858) 342-8328, message us on WhatsApp, or book online.
