Heavy Duty Inspection & Maintenance Program


What is the HD I/M program?

  • Mandates that in order to operate in California, all heavy-duty non-gasoline vehicles with a GVWR of more than 14,000 pounds must pass emissions checks.
  • Comparable to a Smog Check program for large trucks.
  • To assure emissions control systems are maintained and working correctly, periodic inspections are necessary.
  • Guarantees prompt repairs to reduce excess emissions.

Who is impacted by the HD I/M program?

  • Owners and drivers of non-gasoline vehicles traveling in California with a GVWR exceeding 14,000 pounds.
  • Testers who check HD I/M automobiles for compliance.
  • Freight brokers and contractors who operate HD I/M trucks in California.
  • California-based freight facilities that are appropriate and accept HD I/M-eligible trucks on their grounds.
  • OBD test device manufacturers who create and market testing equipment used to conduct compliance checks on HD I/M automobiles.

Vehicles affected by the HD I/M Regulation



  • All non-gasoline heavy vehicles operating in California with GVWR greater than 14,000 lbs.

This includes:

  • All diesel, alternative fuel and hybrid vehicles.
  • All California licensed, out-of-state (OOS) and out-of-country vehicles operating in California.



  • Zero-emission heavy-duty vehicles.
  • Emergency vehicles.
  • Tactical military vehicles.
  • Motor homes registered outside of California used for recreational purposes.
  • New vehicles with engines certified to most stringent optional NOx standard (only for first 4 years of the program).
  • Vehicles with a permanent Historical Vehicle License Plate.
  • *Vehicles operating under a CARB-issued experimental permit.
  • **OOS vehicles operating under a Governor’s emergency declaration.
  • Gasoline heavy-duty vehicles already covered under the Bureau of Automotive Repair’s Smog Check program.

Vehicle Owner Requirements

  • Vehicle owners must ensure all their vehicles operating in California are compliant.

A vehicle is compliant with the HD I/M requirements when:

  • There are no outstanding enforcement actions.
  • The annual vehicle compliance fee is paid(Effective no earlier than 7/1/2023).
  • The owner and vehicle information has been reported (Effective no earlier than 7/1/2023).
  • The vehicle is compliant with the periodic emission testing requirements (Effective no earlier than 1/1/2024).
  • Existing Periodic Smoke Inspection Program requirements apply until HD I/M periodic compliance testing begins in 2024 timeframe.
  • Official start dates dependent on the rollout of the HD I/M program database. CARB will provide notice prior to effective dates.

Vehicle Owner Requirements at Program Launch for HD I/M

  • Starting 1/1/2023
  • High-Emitter vehicle screening
    • Remote emissions monitoring systems (REMS) to detect emissions from moving vehicles
  • A Notice to Submit to Testing (NST) will be issued to any vehicles in California that have been identified as potential high emitters.

Notice to Submit to Testing (NST)

  • NST mandates further testing for vehicles.
  • Must provide CARB with a valid vehicle compliance test within 30 days.
  • If a passing compliance test isn’t provided within 30 days, the HD I/M program will not be followed, and enforcement action may be taken.

Reporting & Compliance Fees for Owners

  • HD I/M database is now being developed.
  • Vehicle owners will be required to record fleet and vehicle information and pay a $30 per vehicle yearly compliance charge.
  • Identify the qualifying vehicles within your fleet by creating an account in the HD I/M database.
    • To avoid duplicating reporting tasks, the HD I/M database will extract vehicle information from existing CARB databases.
  • Annual compliance costs will be paid through a vehicle owner’s account page.

Compliance & Reporting Fee Schedule

Requirements for reporting and compliance fees won’t go into effect until July 1, 2023:

  • Before the primary reporting is required, tutorials for the HD I/M database will be made accessible.