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Heavy-Duty Inspection & Maintenance (HD I/M)

In December of 2021, the California Air Resources Board approved for adoption the HD I/M program in an ongoing effort to meet air quality standards by ensuring heavy-duty vehicle emissions control systems are properly operating throughout the life of the vehicle. The program sets regular testing requirements for all non-gasoline heavy-duty trucks operating in the State and will be tied to DMV registration. Learn more about the requirements, exemptions, and timeline below.

Overview Video

Live ZOOM and in-person training opportunities available. Browse upcoming dates and times at the TruckStop Training and Events page.

HD I/M Regulation Applicability & Exemptions

The HD I/M Regulation requires all diesel, non-gasoline, and alternative fuel trucks and buses with a gross vehicle weight rating (GVWR) over 14,000 pounds to be regularly tested. This is to ensure all emissions related equipment is functioning properly for the life of the vehicle.

The Regulation applies to:
  • California (CA) registered heavy-duty vehicles with gross vehicle weight rating GVWR more than 14,000 pounds; and
  • Non-California registered heavy-duty vehicles operating in CA with GVWR more than 14,000 pounds.
The Regulation does not apply to:
  • Zero-emissions trucks;
  • Military tactical vehicles;
  • Emergency vehicles;
  • New vehicles with engines certified to most stringent optional NOx standard (only for first 4 years of program);
  • Motorhomes registered outside of California;
  • Vehicles operating under an experimental permit;
  • Historical vehicles; or
  • Gasoline vehicles with GVWR over 14,000 pounds;

Compliance Demonstration Requirements

All covered vehicles must demonstrate compliance to legally operate in California. DMV will block registration on California-based vehicles that have not demonstrated compliance.

A covered vehicle will be deemed compliant when:

  • There are no outstanding enforcement actions on the vehicle in question
  • There are no outstanding emissions or OBD-related recalls on the vehicle in question
  • The owner has paid an annual compliance fee to CARB*
  • The owner has reported owner and vehicle information to CARB (owner and vehicle data will be pulled from existing databases, to the extent feasible, and subject to owner verification)**
  • The owner has demonstrated compliance with the periodic vehicle emission testing requirements by submitting a passing compliance test to CARB

*Effective no earlier than 7/1/2023
**Effective no earlier than 1/1/2024

Prior to the asterisked requirements listed above taking effect, CARB will provide a minimum 90-day notice of these requirements to affected entities.

Notice to Submit to Testing

Beginning January of 2023, Roadside Emissions Monitoring Devices (REMD) will be deployed throughout California and begin screening for potential high emitting vehicles. Owners of vehicles identified as potential high emitters will be issued a notice to submit to testing (NST) letter and have 30 days to submit a passing emissions test to CARB. Failure to do so would result in an enforcement violation.

If you receive a Notice to Submit to Testing, please see the “Emissions Testing Methods” section further down on this page for more information on the testing requirements.

Periodic Testing Requirements

PSIP testing is required for in-state fleets until full implementation of the program. Please see information on that program on the TruckStop Opacity FAQ page. After full implementation of the HD I/M program, the periodic testing requirements are as follows:

Periodic testing requirements for emissions related vehicle components:
  • 2013+ Model Year (MY) Engines: On-Board Diagnostics (OBD) equipped vehicles
    • OBD test submission: 2x per year
      • OBD test submission increases to 4x per year after 3 years of 2x per year testing
    • CA Motorhomes: 1x per year
    • On-Road Agricultural (AG) Vehicles: 1x per year
  • Pre-2013 MY engines: Non-OBD equipped vehicles
    • Opacity test submission and visual/functional inspection: 2x per year
    • CA Motorhomes: 1x per year
    • On-Road Agricultural (AG) Vehicles: 1x per year
  • Submit passing test within 90 days before compliance test deadlines
    • CA registered vehicles: based on DMV registration date*
    • Out-of-state registered vehicles: based on last number of VIN**

* Example of periodic compliance dates for a CA registered vehicle: If the vehicle's DMV registration date is March 31, then the vehicle’s periodic submission deadlines would be March 31 and September 30 (6 months later) for a given year.

**Example of periodic testing compliance dates for a non-California registered vehicle:
VIN ending in “5” has compliance deadline of March 31 and a second compliance deadline on September 30 (6 months later)

Emissions Testing Methods

The testing method chosen will be dependent upon if the vehicle being tested is on-board diagnostics (OBD) compliant or not.

OBD equipped vehicles include the following vehicles:

  • Vehicles equipped with a 2013 model year (MY) and newer diesel or diesel hybrid engines.
  • Vehicles equipped with a 2018 MY or newer alternative fuel or alternative fuel hybrid engines.
All other vehicles are considered non-OBD vehicles.

Below are the methods for OBD and non-OBD vehicles:

  • Covered vehicles must provide a data submission (No MIL-related issues can be present)
    • A telematics service provider device that meets CARB’s data format submission requirements
    • Hand-held scan tools and plug-in dongles that meet CARB’s data submission requirements - Testing must be performed by a HD I/M tester
  • Diesel vehicles must pass the SAE J-1667 opacity test
    • Performed with opacity testing equipment that meet the SAE J1667 specifications
    • Non-diesel vehicles are exempt from the opacity test
  • All covered vehicles must pass a visual/functional inspection of vehicle’s emissions control components to check for tampering
  • Testing performed by a HD I/M tester.

Approved HD I/M Tester

To ensure consistency, the HD I/M program requires that all non-telematics emissions testing and reporting is performed by approved HD I/M testers. Any individual from any state is eligible to complete CARB approved training to become an approved tester. Approved HD I/M testers will submit vehicle compliance tests through tester accounts created in the HD I/M database system. Additionally, approved HD I/M testers will need to renew their credentials every two years.

The online training will include the following training modules and a respective exam:

  • Regulatory requirements
  • Smoke opacity compliance testing
  • OBD compliance testing
  • Vehicle emissions control inspections

Freight Contractor, Broker, and Applicable Freight Facility Requirements

  • Applicable Freight Facilities (Seaport Facilities and Intermodal Railyards) must check that only compliant vehicles enter/operate on their properties or maintain records of non-compliant vehicles.
  • Freight Contractors and Brokers must check for compliance documents and retain records

HD Inspection & Maintenance Regulation Timeline. In mid 2022 Certified tester training class will be available. January 2023 - Phase 1 - Reporting required for initial owner and vehicle information in CARB's HD I/M database. High-emitter vehicle screening and follow up compliance testing begins. July 2023 - Phase 2 - Compliance checked during California DMV registration. CHP/CARB Begin enforcing compliance certificate requirement. Freight contractor/facility verification begins. January 2024 - Phase 3 - Full implementation. Periodic compliance testing requirement begins.

View the TruckStop Current Opacity Inpection Programs page for existing requirements.