CARB Clean Truck Check: keep your emissions checks compliant without slowing down your fleet

Antonio Mendoza

For years, emissions compliance followed a pattern where a vehicle was scheduled for testing, removed from service, sent to a shop, passed inspection, and returned to service. If nothing failed between tests, the system held together. Another method was having a third party tester come out to the yard and do testing on all vehicles that needed; it worked, but it still compressed downtime into a single window, pulling multiple units out of rotation at once, creating short-term capacity gaps, and forcing operations to either delay routes, reshuffle assignments, or absorb the hit in service levels.

California’s Clean Truck Check (CTC) changes how that system behaves. Born from Senate Bill 210 in 2019 and administered by the California Air Resources Board (CARB), the program became effective October 1, 2024, with the first deadlines on January 1, 2025. The program evaluates emissions data submitted from vehicles in operation, so issues that previously stayed hidden between inspections now surface when a test is due. Mechanical faults and process gaps show up together.

Nearly all diesel, alternative fuel, and hybrid heavy-duty vehicles over 14,000 pounds in California are included, regardless of where they are based. That means out-of-state fleets passing through California carry the same obligations as in-state operators. Compliance now depends on regular checks over time rather than a single successful test.

Why was Clean Truck Check implemented?

Heavy-duty diesel trucks over 14,000 pounds are among the largest contributors to California’s air quality problems, responsible for the majority of on-road NOx and PM 2.5 emissions even after decades of regulatory efforts to reduce them. The issue isn’t just older trucks. Modern vehicles are equipped with aftertreatment systems designed to control emissions, but when those systems malfunction, pollution spikes. Traditional testing schedules weren’t catching it fast enough. Clean Truck Check closes that gap by requiring consistent, ongoing emissions verification rather than periodic snapshots. When fully implemented, CARB projects the regulation will cut statewide NOx emissions by more than 81 tons per day by 2037 and prevent over 7,500 premature deaths.

What are the Clean Truck Check emissions testing requirements?

The CTC requirements are clearly defined. Complete a test, meet a deadline, submit a result. In practice, each step depends on coordination: vehicles rotate in and out of service, shops manage multiple priorities, routes shift, drivers work against tight schedules, and data is tracked across multiple systems.

Compliance deadlines are assigned per vehicle and tied to either the DMV registration expiration date for California-registered vehicles, or the last digit of the VIN for out-of-state and DMV-exempt vehicles. Each vehicle’s specific deadlines are available in its CTC-VIS account. Passing tests can be submitted up to 90 days before a compliance deadline so fleets have a window to test early and still have time to make repairs and retest if a vehicle doesn’t pass. Wait too long in that window, and there’s little room to recover before the deadline hits.

Semi-annual testing has been required since January 2025. Beginning October 2027, vehicles subject to OBD-based testing will be required to text four times per year. Each additional cycle introduces more scheduling, tracking, and opportunities for delay. Small gaps accumulate, and recovery begins to require more effort than prevention.

Why do good teams fall behind on California emissions checks?

Most compliance issues begin with reasonable operational decisions. A vehicle stays in service to meet demand, a repair takes priority over a scheduled test, or a deadline is missed during a busy cycle. Each decision solves an immediate problem, but over time they create misalignment with compliance requirements.

CARB’s Clean Truck Check program evaluates outcomes based on submitted results. A compliant result must be provided within a defined window. Miss it, and enforcement follows: flags, registration holds, and vehicles taken out of operation.

What will the 2027 testing changes mean for your fleet?

Quarterly testing increases the load across operations, maintenance and administration. That means dispatchers and fleet managers need to schedule and complete more tests. Administrative demands grow, missed windows become more likely, and costs rise with the level of effort required to keep up.

Delays begin to overlap. A missed test affects the next cycle, recovery windows narrow, and fleet operators spend more time reacting instead of maintaining steady compliance. For fleets who have to manage Clean Truck Checks as a manual scheduled task, the operational drain becomes visible through longer downtime, shifting schedules, and lost revenue.

Does it matter how your fleet manages CARB compliance?

Many fleets still manage Clean Truck Check as a scheduled maintenance task, where testing is planned, tracked, and completed as a separate activity. That model made sense when testing happened once a year. It’s harder to sustain at twice a year, and at four times a year starting in October 2027, the math stops working.

Compounding the challenge, each vehicle operates in its own compliance window (often tied to registration timing or VIN) so deadlines are staggered across the fleet rather than aligned. What used to be single event becomes a continuous scheduling problem. Vehicles must be taken out of service, coordinated with emissions check locations, and returned to operations on different timelines, increasing both time and cost. Then, if a vehicle fails, that entire sequence repeats under time pressure, because the compliance deadline hasn’t moved.

Conversely, automating CTC checks through telematics distributes compliance across daily operations. Approved telematics devices capture vehicle data during normal use but only perform and submit an emissions compliance scan at the start of each 90-day testing window. If the vehicle passes, no additional data is sent to CARB for that period; only what is required, when it is required. Issues appear earlier, giving time to respond within existing workflows, and fewer steps depend on timing and manual follow-through. Along with automating checks, these approved telematics devices can also alert fleet managers to preventive maintenance needs, helping maintain vehicle health and reduce the likelihood of future emissions check failures.

What does it look like to automate your emissions checks?

Zonar has offered a CARB-certified, automated path to Clean Truck Check compliance for over a year, when it became the first telematics provider to receive a CARB executive order for continuously connected remote OBD testing. The V4 telematics device, installed directly on a vehicle and connected to the OBD system, captures emissions data continuously during normal operation and submits it automatically. No separate testing event, no shop visit, no scheduling coordination.

That’s been the baseline. Zonar now extends that model with an additional installation path, becoming the first company in California certified for Clean Truck Check compliance through OEM-installed vehicle hardware. This means fleets can use factory-installed telematics where available, alongside Zonar devices where needed, to support compliance across mixed vehicles, protocols and configurations. OEM telematics (sensors and software built directly into the vehicle) collect engine, component, and vehicle data during normal operation. That data can now be submitted and accepted for compliance without requiring a separate test.

For vehicles like Thomas Built Buses, Freightliner Cascadia, and Western Star trucks that come equipped with compatible, Zonar-certified OEM telematics hardware, there’s no additional equipment to install and no need to route vehicles through a shop. Activation happens at the system level, and data begins flowing through an approved compliance pathway as part of normal operation.

Zonar is also the only provider whose executive order explicitly permits compliance through a hardwired vehicle harness, not just a direct OBD port connection. That matters for vehicles that are factory-equipped with Zonar hardware, where compliance can be supported without additional installation or modification.

Either way, V4 aftermarket install or OEM-installed hardware, the outcome is the same: vehicle data flows through an approved compliance pathway automatically, starting on the first day of the 90-day testing window, without disrupting operations.

How does your CTC check process change in practice?

The shift is straightforward to describe but significant in practice. Instead of building compliance around a testing event, you build it into how vehicles already operate.

Using an automated emissions check through either an approved telematics device or an approved OEM-installed device allows for complete automation. Your vehicles are collecting and submitting compliant emissions data automatically during every route. Vehicles stay in service while data is collected and submitted automatically, issues surface earlier in the cycle, and fleet-wide coverage expands without adding coordination overhead.

What that means day-to-day:

The work disappears and shifts into the flow of operations where it can be managed proactively rather than reactively. You get time back and less downtime with your vehicles.

Issues surface earlier. Because data is collected continuously, emissions faults show up during normal operation, not on the day of a scheduled test. That gives your maintenance team time to address problems before they become violations, within your existing workflow rather than outside it.

Fleet-wide coverage scales without added effort. Whether you’re managing 10 vehicles or 1,000, the compliance process doesn’t grow more complex as your fleet does. Each vehicle handles its own submission. Your job is to monitor, not to coordinate.

The 2027 shift to quarterly testing doesn’t change any of that. Four cycles a year with automated compliance looks the same as two. The manual model doesn’t have that flexibility.

How does this impact you with the 2027 CARB CTC changes?

Under CARB’s Clean Truck Check (CTC) program, emissions testing frequency will increase to quarterly in 2027. Coordination demands will continue to grow. The difference will come down to how compliance is handled inside your operation.

Fleets that continue to manage compliance as a scheduled task will see greater time demands, administration, vehicle out of service time and increased risk of missed deadlines as the system scales.

Fleets that automate compliance into daily operations reduce that dependency on timing, scheduling, and manual follow-through.

What to do next if you want to improve your Clean Truck Check process?

If your current process depends on pulling vehicles out of service, coordinating tests, and tracking deadlines across systems, how will you sustain the workload on a quarterly frequency?

If your vehicles are already equipped with Zonar OEM telematics or a Zonar V4 device, you may already have a path to reduce that load. To learn more about how Zonar’s certified approach automates CARB emission checks, without interrupting service schedule a meeting with a Zonar consultant. Don’t treat compliance like a calendar event. Build it into how your fleet already operates.