ATCM 93120 Phase 2 is California's stricter emissions standard for heavy-duty diesel trucks, effective from 2027 onward

California's Airborne Toxic Control Measure (ATCM) 93120 Phase 2 sets new limits on particulate matter and nitrogen oxides from diesel trucks and buses. The California Air Resources Board (CARB) adopted this rule to reduce air pollution in communities near highways, ports, and warehouses. If you own or operate heavy-duty diesel vehicles in California, Phase 2 requirements will affect which trucks you can use and when you must replace older ones.

Phase 2 becomes mandatory on January 1, 2027. The rule applies to trucks and buses with model years 2010 and older that operate in California. Vehicles that do not meet the new emissions standards cannot legally operate in the state after that date, with limited exceptions for emergency vehicles and certain agricultural uses.

Key Takeaways

  • Phase 2 requires heavy-duty diesel trucks model year 2010 and older to be retrofitted or retired by January 1, 2027.
  • The rule covers particulate matter and nitrogen oxide emissions, with stricter limits than Phase 1, which took effect in 2014.
  • Trucks that meet Phase 2 standards must have a CARB-verified retrofit device or be model year 2011 or newer with approved emissions controls.
  • CARB maintains a list of compliant vehicles and approved retrofit technologies on its website, updated as manufacturers certify new equipment.
  • Fleets operating in California should begin planning now, as retrofit parts and replacement vehicles may face supply delays as the important date approaches.

How Phase 2 differs from Phase 1

Phase 1 of ATCM 93120 took effect on January 1, 2014, and required trucks model year 2009 and older to be retrofitted or removed from California roads. Phase 2 tightens the standard by lowering the model year cutoff to 2010. This means trucks that were compliant under Phase 1 may no longer meet the new emissions limits.

Phase 2 also reduces the allowable emissions thresholds themselves. A truck that passed Phase 1 inspection with a retrofit device may need a newer or upgraded device to meet Phase 2 limits. CARB publishes the specific particulate matter and nitrogen oxide limits in its technical documents, and manufacturers update their retrofit certifications as technology improves.

Which vehicles are covered by Phase 2

Phase 2 applies to diesel-powered heavy-duty vehicles with a gross vehicle weight rating (GVWR) of 10,001 pounds or more. This includes semi-trucks, delivery trucks, dump trucks, concrete mixers, and transit buses. Gasoline-powered trucks and vehicles under 10,001 pounds GVWR are not subject to the rule.

The rule covers any vehicle that operates in California, regardless of where it is registered. A truck registered in Nevada or Oregon must still comply if it drives into California. School buses, emergency vehicles, and military vehicles have exemptions, though the exemptions are narrow and require documentation.

Compliance options before January 1, 2027

You have three main paths to compliance. The first is to retrofit your truck with a CARB-verified emissions control device. CARB maintains a list of approved retrofit manufacturers on its website, organized by vehicle type and model year. Retrofit costs vary widely—typically $3,000 to $15,000 depending on the device and truck—but some air districts offer rebate programs that cover part of the cost.

The second option is to replace your truck with a model year 2011 or newer that has factory emissions controls meeting Phase 2 standards. New and used trucks that meet the standard are listed in CARB's compliant vehicle database. This is the most expensive option upfront but eliminates ongoing retrofit maintenance.

The third option is to retire the vehicle and stop operating it in California. If your truck is old enough that retrofit costs exceed its value, retirement may be the practical choice. Some air districts run vehicle retirement programs that offer cash incentives for scrapping compliant vehicles.

How to verify your truck meets Phase 2 standards

CARB publishes two searchable databases: one for compliant vehicles and one for approved retrofit devices. To check if your truck is listed as compliant, you need the vehicle identification number (VIN), model year, and engine type. The CARB website has a lookup tool where you enter this information and receive confirmation of compliance status.

If your truck is not listed as compliant, you can search the retrofit device database by vehicle model year and engine type. Each approved device lists which vehicles it fits and what emissions levels it achieves. If you install an approved device, keep the installation receipt and have the retrofit installer provide CARB documentation proving the work was done correctly.

Air district rebates and financial support

California's air districts—South Coast AQMD, San Joaquin Valley APCD, Bay Area AQMD, and others—offer rebate programs to help offset retrofit and replacement costs. Rebate amounts and may be able to access rules vary by district and change year to year. Some districts prioritize small businesses, owner-operators, and fleets serving disadvantaged communities.

To find rebates in your area, contact your local air district directly or visit its website. You typically must explore before purchasing the retrofit or vehicle, and the district may require proof of income, business registration, or residency in the district. Processing times range from a few weeks to several months, so plan ahead if you are counting on a rebate to make the purchase affordable.

What happens if your truck does not comply by the important date

Operating a non-compliant truck in California after January 1, 2027, is illegal. CARB and local law enforcement can issue citations and fines. The penalties start at several hundred dollars per violation and increase for repeat offenses. A truck can be impounded if caught operating without compliance.

Insurance companies may also deny claims if a vehicle was operating illegally at the time of an accident. Customers and freight brokers increasingly verify fleet compliance before hiring, so non-compliant trucks may become impossible to use for work even before enforcement begins.

Frequently Asked Questions

Can I get an extension if I cannot afford to retrofit or replace my truck by 2027?

CARB does not grant individual extensions to the Phase 2 important date. However, some air districts have hardship programs or extended rebate funding. Contact your local air district to ask whether a hardship exemption or additional financial support is available in your area.

Do I need to get my truck inspected to prove it meets Phase 2 standards?

You do not need a formal inspection if your truck is listed in CARB's compliant vehicle database or has an approved retrofit device installed with documentation. However, if you are stopped by law enforcement, you should have proof of the retrofit installation or a printout from the CARB database showing your vehicle's compliance status.

What if I own a truck that is registered outside California but I drive it into the state?

Phase 2 applies to any truck operating in California, regardless of registration state. If you regularly drive into California, your truck must meet Phase 2 standards by the important date or you cannot legally operate it in the state.

Are there any vehicle types exempt from Phase 2?

Emergency vehicles, military vehicles, and school buses have exemptions, but they must be clearly marked and used only for their exempt purpose. Vehicles used for any commercial or non-emergency purpose do not may have access to for the exemption.

Where can I find the CARB compliant vehicle and retrofit device databases?

Both databases are on the California Air Resources Board website under the ATCM 93120 section. You can search by vehicle model year, engine type, or retrofit manufacturer. The databases are updated regularly as new devices are certified.