California’s Clean Truck Check (CTC) program represents one of the most important changes in trucking regulations in recent memory. The state is no longer relying on occasional inspections or targeted enforcement to catch high-polluting vehicles. Instead, California now monitors truck emissions every day, in real time, using an expanding network of Remote Emissions Monitoring Devices (REMDs).

For drivers, owner-operators, and fleet managers, understanding the Clean Truck Check — and the technology behind it — is critical to staying compliant, avoiding fines, and keeping trucks legally operating in the state. This blog explains what the Clean Truck Check requires, how REMDs work, which companies are leading this technology shift, and how DPF Guys can help fleets and drivers stay ahead of these strict new rules.

The Basics of California’s Clean Truck Check

The Clean Truck Check was developed by the California Air Resources Board (CARB) after Senate Bill 210 was signed into law in 2019. Its purpose is straightforward: ensure that heavy-duty diesel and alternative-fueled trucks continue to meet emissions standards throughout their operating lives — not just when new.

The program officially launched in January 2023 with the use of roadside monitoring technology.
Beginning in October 2024, trucks must undergo regular compliance testing, and by October 2027, testing frequency will increase for newer, OBD-equipped trucks. Any vehicle over 14,000 pounds GVWR operating in California falls under these rules, including out-of-state trucks. There are limited exemptions, mostly for emergency vehicles, but the vast majority of trucks on California roads are required to comply.

What Compliance Looks Like for Drivers and Fleets

Under the Clean Truck Check, drivers and fleet owners must take specific steps to stay compliant. Each truck must be registered in CARB’s online Vehicle Inspection System (CTC-VIS), and operators must pay an annual compliance fee — $31.18 per vehicle in 2025.

Emissions testing requirements depend on the type of truck. Newer trucks with On-Board Diagnostics (OBD) systems must complete emissions tests twice a year beginning in 2024, increasing to four times a year by 2027. Older trucks without OBD systems are subject to a visual inspection and opacity (smoke) test twice annually.

If a vehicle is found to emit more pollution than allowed, either through a compliance test or a roadside scan, the operator must correct the problem and submit passing results within 30 days. Failure to comply can lead to heavy fines, registration holds, and operational shutdowns.

The Costs of Staying Compliant

Compliance is not free, and drivers should plan accordingly. Emissions testing typically costs between $70 and $150 per test for OBD-equipped vehicles and $60 to $120 per test for older trucks requiring opacity testing. Because most trucks will be tested multiple times a year, these costs are now a regular part of doing business in California — not a one-time expense.

A New Era of Enforcement: How Remote Emissions Monitoring Devices (REMDs) Work

The biggest change under the Clean Truck Check is not the testing schedule — it’s how CARB enforces emissions compliance in the first place. California has deployed a statewide network of Remote Emissions Monitoring Devices (REMDs) at major highways, ports, and freight corridors. These small, roadside units measure truck emissions as vehicles drive past at highway speeds, without stopping them or requiring a manual inspection.

Each REMD uses a combination of technologies:

• Infrared and ultraviolet sensors detect gases like NOx and hydrocarbons
• Laser sensors measure particulate matter (soot)
• High-speed cameras capture license plates to match emission readings with specific vehicles
• Environmental sensors adjust readings for temperature, wind, and humidity

The entire process happens in about one second. Drivers often pass an REMD without even realizing they were scanned. If a truck’s emissions are too high, the system automatically generates a Notice to Submit to Testing (NST), giving the operator 30 days to complete and pass a certified test. If ignored, the truck’s DMV registration can be blocked, effectively removing it from legal operation.

The Scale of REMD Coverage

While CARB has not disclosed the exact number of deployed REMDs, the network already covers most major trucking routes, and continues to expand. For most trucks operating regularly in California, it is not a matter of if they will be scanned — it is a matter of how often. Any assumption that emissions enforcement can be avoided by avoiding weigh stations or rare inspections is now outdated. With REMDs, monitoring happens constantly and automatically.

The Technology Behind REMDs: Key Players and Innovations

Several established companies supply the technology powering California’s Clean Truck Check:

• Opus Group, based in Sweden and the United States, is a leader in roadside remote sensing devices, specializing in real-time vehicle emissions measurement for regulatory programs around the world.
• ABB, a Swiss-American corporation, supplies precision industrial emissions monitoring systems that support calibration and validation of remote roadside measurements.
• HORIBA, a Japanese-American firm, is globally recognized for emissions analysis tools used in labs, on vehicles, and increasingly in mobile roadside units.

Together, these companies form the technological backbone of California’s real-time emissions enforcement efforts.

The Rise of Startups and the Role of AI in Emissions Monitoring

Beyond the established players, a new generation of startups is advancing roadside emissions monitoring using artificial intelligence (AI) and real-time data analytics. Some notable companies include:

• Global MRV, offering portable emissions measurement systems (PEMS) that provide real-world emissions data for moving trucks.
• Valarm, a California-based firm that adapts industrial IoT technology for roadside emissions and air quality monitoring.
• GaiaHub, which uses advanced license plate recognition and real-time data analysis to track traffic emissions.

AI is not just a buzzword in this field — it is a practical tool that improves REMDs by:

• Sorting real emission violations from environmental noise
• Detecting anomalies faster than human inspectors
• Predicting which trucks are likely to become high emitters based on early warning signs

As AI adoption grows, emissions enforcement will only become faster, smarter, and more precise.

What Happens If You Fail a Scan?

The Clean Truck Check system is designed to move quickly. If an REMD scan identifies your truck as a high emitter, CARB will send a Notice to Submit to Testing. You will have 30 days to complete a certified test and prove compliance.

Failing to act can result in registration holds, fines, and potentially having your truck grounded — a costly disruption no business can afford.

How DPF Guys Helps You Stay Ahead

At DPF Guys, we built our services around helping truckers and fleets meet the demands of the new Clean Truck Check system.

Our services include:

• Certified OBD and opacity emissions testing
• Mobile testing to your yard or location
• DPF cleaning, SCR repairs, and EGR cooler maintenance to fix emission system problems fast
• Compliance support to help register vehicles and manage testing schedules
• Preventative maintenance programs designed to catch and fix issues before they trigger a scan failure

We understand not just the rules — but also the technologies and enforcement methods behind them.
Our goal is simple: keep your trucks compliant, operational, and profitable.