Your complete guide to California's heavy-duty vehicle emissions testing requirements. Everything fleet owners and operators need to know about compliance.
Clean Truck Check (formerly known as Heavy-Duty Inspection and Maintenance or HD I/M) is California's mandatory emissions testing program for heavy-duty vehicles. Approved by the California Air Resources Board (CARB) in December 2021, this program ensures that emissions control systems on trucks, buses, and other heavy-duty vehicles are functioning properly.
The program applies to nearly all diesel and alternative fuel vehicles with a Gross Vehicle Weight Rating (GVWR) over 14,000 pounds that operate on California public roads and highways — even if the vehicle is registered in another state.
| Vehicle Type | Testing Required |
|---|---|
| Semi-trucks and tractors | |
| Delivery and distribution trucks | |
| Buses (transit, shuttle, school) | |
| Motorcoaches | |
| Heavy-duty work trucks | |
| Diesel RVs/Motorhomes (14,001+ lbs) | |
| Diesel hybrid vehicles | |
| Alternative fuel vehicles (natural gas, propane) | |
| Out-of-state vehicles operating in CA |
Not sure if your vehicle qualifies? Check your door jamb sticker for the manufacturer's GVWR. If it's over 14,000 lbs and powered by diesel or alternative fuel, you likely need testing.
Applies to:
Test Type:
OBD (On-Board Diagnostics) scan using CARB-certified testing device
What happens:
A credentialed tester connects to your vehicle's OBD port and downloads an emissions data snapshot. Results are uploaded to CARB in real-time.
Pro tip:
Don't clear diagnostic codes or disconnect your battery before testing. Your vehicle needs time to complete OBD system checks.
Applies to:
Test Type:
Smoke opacity test + visual inspection
What happens:
The tester performs a smoke opacity measurement and visually inspects your emissions control equipment for proper operation and tampering.
Applies to: Non-commercial motorhomes registered in California for recreational or emergency use with GVWR over 14,000 lbs
Testing frequency: Once per year (annual)
Commercial motorhomes follow the standard semi-annual testing schedule.
Applies to: Vehicles meeting CARB's agricultural vehicle definition
Testing frequency: Once per year (annual)
You must attest that your vehicle meets the agricultural definition when registering in CTC-VIS.
| Vehicle Type | Testing Frequency |
|---|---|
| Most commercial vehicles (OBD & non-OBD) | 2 times per year (semi-annual) |
| California motorhomes (recreational) | 1 time per year (annual) |
| Agricultural vehicles | 1 time per year (annual) |
Important Change: Starting October 2027, OBD-equipped vehicles (2013+ diesel, 2018+ alternative fuel) will be required to test 4 times per year (quarterly).
| Vehicle Type | Testing Frequency (Oct 2027+) |
|---|---|
| OBD-equipped vehicles | 4 times per year (quarterly) |
| Non-OBD vehicles | 2 times per year (semi-annual) |
| California motorhomes (recreational) | 1 time per year (annual) |
| Agricultural vehicles | 1 time per year (annual) |
Your compliance deadlines are tied to your DMV registration expiration date:
Example: If your registration expires January 31st, your deadlines are January 31st and July 31st.
Deadlines are based on the last digit of your VIN:
| Last VIN Digit | Compliance Months |
|---|---|
| 1 | January & July |
| 2 | February & August |
| 3 | March & September |
| 4 | April & October |
| 5 | May & November |
| 6 | June & December |
| 7 | July & January |
| 8 | August & February |
| 9 | September & March |
| 0 | October & April |
Create an account in CARB's Clean Truck Check Vehicle Inspection System (CTC-VIS) and report your vehicle(s).
CTC-VIS Registration Portal$31.18 per vehicle (2025). Payment must be made through CTC-VIS via credit/debit card or eCheck. Paper checks are NOT accepted.
Tests can be submitted up to 90 days before your compliance deadline. Find a credentialed tester or schedule mobile testing. Plan ahead in case repairs are needed.
Testing must be performed by a CARB-credentialed tester using approved equipment.
Once compliant, download your certificate from CTC-VIS. Keep it accessible in your vehicle.
| Consequence | Details |
|---|---|
| DMV Registration Hold | Cannot renew registration until compliant |
| Port/Railyard Denial | Non-compliant vehicles may be denied entry |
| Roadside Enforcement | CHP and CARB conduct inspections at weigh stations |
| Fines | Up to $10,000 per vehicle per day |
| Tampering Penalties | Up to $37,500 per violation for modified emissions systems |
You'll receive a detailed report showing the issue
You have 90 days from your original deadline to make repairs and retest
Schedule a retest after repairs are complete
We offer discounted retesting rates
Don't wait until your deadline approaches. Schedule your Clean Truck Check testing today and stay compliant with California regulations.
CTC Mobile Services brings testing directly to your location — at your warehouse, yard, or fleet facility. No downtime. No towing. No hassle.
Last updated: January 2026
This page is provided for informational purposes. For official requirements, always refer to CARB's Clean Truck Check program page.