California's Clean Truck Check program has already changed how owners think about emissions. Testing that used to be an afterthought is now a regular part of keeping a heavy duty truck registered and on the road.
And the schedule is about to get tighter. Starting in October 2027, OBD equipped heavy duty vehicles will be tested four times per year instead of twice. For fleets in Ontario, Fontana, Riverside, Corona, Pomona and across the Inland Empire, that means more tests, more deadlines, and less room for a truck with a lingering emissions problem.
Here is what is changing, who is affected, and how to turn this requirement into something that works in your favor.
A Quick Refresher: What Is Clean Truck Check?
Clean Truck Check is the California Air Resources Board's heavy duty inspection and maintenance program. Think of it as smog check for big trucks. It applies to heavy duty vehicles over 14,000 pounds GVWR that operate on public roads in California, including covered on road vehicles powered by off road engines, subject to the program’s exemptions.
How vehicles are tested today
- 2013 and newer diesel engines: an OBD scan using a CARB certified device.
- 2012 and older diesel engines: a smoke opacity test plus a visual inspection of emissions control equipment.
- 2018 and newer alternative fuel engines: an OBD test. Older covered alternative fuel engines use a visual inspection.
- Off road engines: opacity and visual inspection, regardless of model year.
How often
- Most vehicles: twice a year today.
- Agricultural vehicles and California registered non commercial motorhomes: once a year.
- Starting October 2027: four times a year for OBD equipped vehicles. Motorhomes and agricultural vehicles stay annual.
Your due dates are listed in your CTC VIS account, and passing tests can be submitted up to 90 days before a deadline.
What Quarterly Testing Really Means for Your Fleet
On paper, it is just two more tests a year. In practice, it changes the math.
- Small problems become deadline problems. Today, a truck with an intermittent NOx sensor fault might sneak through two tests a year. With four tests, the odds of a failed test go up.
- Scheduling gets harder. A fleet of 20 trucks goes from 40 tests a year to 80. Without a plan, someone ends up chasing deadlines.
- Failed tests cost more than the repair. The real cost is the truck that cannot be dispatched while you wait for parts and a retest.
- Healthy trucks win. A truck with a clean EGR system, a working DPF and good sensors passes quickly every time. Quarterly testing rewards owners who maintain proactively.
Why Trucks Fail Clean Truck Check
For OBD vehicles, the scan reads stored fault codes and readiness monitors. The most common reasons for trouble we see:
- Active emissions related fault codes such as NOx sensor, DEF quality or EGR flow faults
- Readiness monitors not set after a recent repair or battery disconnect
- Aftertreatment problems like a plugged DPF or failing SCR system
- Tampering or missing equipment, which is a fast way to fail
For older non OBD trucks, excessive smoke opacity and missing or damaged emissions labels are common issues.
Our guide to EGR vs DPF warning signs explains many of these problems in plain language.
The Bigger Picture: Where Emissions Rules Are Headed
It helps to understand the larger trend, because it shapes the decisions you will make over the next few years.
- Federal rules are shifting. The EPA's 2027 NOx standard of 0.035 grams per horsepower hour remains, but in 2026 the EPA proposed changes to compliance, including shorter emissions warranty periods and replacing many DEF derates with driver warnings. These are proposed changes, not final requirements. Check the EPA rulemaking page for the latest status.
- Engine makers are adjusting their launch plans. Cummins, for example, announced a phased launch with its new X15 starting limited production in January 2027.
- California is focusing on the trucks already on the road. Clean Truck Check targets real world emissions of existing vehicles, which is why testing frequency is increasing.
Our outlook: many fleets will keep their current trucks longer while new 2027 technology settles in. That makes in-use emissions health more important than ever. Owners who treat emissions maintenance like brake maintenance, routine and scheduled, will have the easiest time.
A Simple Playbook for Staying Ahead
- Know your dates. Log into CTC VIS and put every truck's due date on one calendar.
- Test early. You can submit a passing test up to 90 days before the deadline. Testing early gives you time to fix a problem without missing the deadline.
- Combine visits. Pair your Clean Truck Check test with your 90 day BIT inspection or preventive maintenance. One visit, multiple boxes checked.
- Fix codes when they appear. Do not wait for the test to find them.
- Keep records together. Inspection reports, repair orders and test results in one place make audits and terminal inspections easier.
Serving Fleets Across the Inland Empire
Our Ontario shop is central to the Inland Empire freight corridor along the 10, 15 and 60. We help owners and fleets with Clean Truck Check testing and emissions repairs from:
- Ontario, Rancho Cucamonga and Upland
- Fontana, Rialto and Bloomington
- Chino, Chino Hills and Eastvale
- Pomona, Claremont and Montclair
- Riverside, Jurupa Valley and Corona
If your truck fails, we can diagnose and repair it in the same building, then retest. That keeps your truck moving instead of bouncing between a tester and a repair shop.
Learn more on our CARB compliance service page, or read our earlier articles: Your Roadmap to CARB Compliance and Clean Truck Check in Ontario, CA: Deadlines, Testing, Failures and Repairs.
Why Fleets Trust Rapid Diesel With CARB Compliance
Rapid Diesel Repair holds California CARB emissions compliance certifications and full state and federal DOT certifications. We have served Inland Empire owners for more than 10 years and have earned more than 315 five star Google reviews for fast turnaround and quality work. Financing is available for larger repairs.
Visit us at 251 Kettering Dr, Ontario, CA 91761, or call (909) 701 8755.
Official references: EPA proposed emissions rule and CARB testing requirements.
Frequently Asked Questions
When does Clean Truck Check go to four tests a year? Starting October 2027 for OBD equipped heavy duty vehicles. Non commercial motorhomes and agricultural vehicles stay on an annual schedule.
Which trucks need Clean Truck Check? Heavy duty vehicles over 14,000 pounds GVWR that operate on public roads in California, including out of state trucks that operate in the state.
How early can I test? You can submit a passing test up to 90 days before your deadline.
What happens if my truck fails? The vehicle should be repaired and retested before the deadline. Common causes include active emissions fault codes and aftertreatment problems.
Where can I get a CARB compliance test near Riverside, Corona or Pomona? Rapid Diesel Repair in Ontario, CA serves the Inland Empire. Call (909) 701 8755.
Why This Matters For Your Vehicle
A service decision affects more than the part being repaired. It affects your next trip, your operating costs and the time your vehicle is available. Keep inspection records, follow the engine and chassis manufacturer’s service schedule, and explain when each symptom appears. A diagnosis based on actual test results helps you compare repair options and plan maintenance before a small concern becomes a larger interruption.
Written by the Rapid Diesel Repair team, Ontario, CA. Serving the Inland Empire for more than 10 years with DOT and CARB certified diesel repair.