If you own or operate a diesel truck, bus, or motorhome in California, the CARB Clean Truck Check program applies to you. Launched by the California Air Resources Board (CARB), the program requires periodic emissions testing to ensure heavy-duty diesel vehicles meet the state's air quality standards.
Whether you run a single box truck or a fleet of semis, understanding what testing you need — and when — is essential to avoiding fines and keeping your vehicles on the road.
Two types of testing: OBD and OVI
The Clean Truck Check program uses two distinct testing methods, depending on your vehicle's engine year and configuration.
OBD (On-Board Diagnostics) testing
OBD testing applies to most diesel vehicles with engines from 2013 and newer. The test connects to your truck's OBD port — the same diagnostic port your mechanic uses — and reads emissions-related fault codes directly from the engine control module.
The test takes about 10 to 15 minutes per vehicle. If your OBD system reports no active emissions faults, you pass. It is the faster and less expensive of the two methods — $75 per vehicle with NorCal CARB Mobile.
OVI (Opacity / Visual Inspection) testing
OVI testing, also called a smoke opacity test or SAE J1667 test, applies to vehicles with pre-2013 engines or engines that do not have a compatible OBD system. This test measures the density of smoke coming from the exhaust under a controlled snap-acceleration procedure.
A certified tester uses a calibrated opacity meter to measure the smoke level as a percentage. If the reading is below the allowable threshold, you pass. OVI testing costs $199 per vehicle with NorCal CARB Mobile.
Who needs a Clean Truck Check?
The program applies broadly to heavy-duty diesel vehicles operating in California:
- Class 4 through Class 8 diesel trucks (over 14,000 lbs GVWR)
- Diesel buses and transit vehicles
- Diesel motorhomes and RVs
- Agricultural diesel vehicles (with some exemptions)
- Out-of-state trucks operating in California
If your vehicle has a diesel engine and operates on California roads, you almost certainly need periodic Clean Truck Check testing. The consequences of non-compliance include fines starting at $1,000 per vehicle and potential registration holds.
How often do you need testing?
As of 2026, CARB requires testing at least once per year for most vehicles, with some fleet operators required to test twice per year. Testing frequency depends on your vehicle's compliance history and fleet size.
CARB tracks compliance through the CTC-VIS (Clean Truck Check Vehicle Information System) portal. Your test results are submitted electronically by your tester — you do not need to file anything separately.
Mobile testing vs. stationary testing centers
You have two options for getting tested: drive to a stationary testing center, or have a mobile tester come to you.
For fleet operators with multiple trucks, mobile testing saves hours of downtime. Instead of driving each truck to a center and waiting in line, a certified tester comes to your yard and tests every vehicle on-site. A fleet of six trucks that would take an entire day at a testing center can be done in under two hours at your location.
NorCal CARB Mobile provides on-site testing across Sacramento, Stockton, Fairfield, San Jose, and the Bay Area — including Saturday appointments.
What happens if you fail?
If your vehicle fails its Clean Truck Check, you are given a window to make repairs and retest. Common reasons for failure include faulty sensors, exhaust leaks, DPF (diesel particulate filter) issues, and engine control module faults.
Your tester can often identify the specific issue during testing and point you toward the right repair. After repairs, you schedule a retest to clear the failure and restore compliance.
Get tested
NorCal CARB Mobile makes compliance straightforward. We come to your yard, test your vehicles on-site, and handle the CARB paperwork. OBD testing starts at $75, OVI at $199, and we offer fleet discounts for multi-truck yards.
Book a test or call (916) 890-4427 to schedule same-week testing.
Ready to get compliant?
Book mobile Clean Truck Check testing anywhere in Northern California.