On-Board Diagnostics (OBD) Program

This page last reviewed January 14, 2019.


On-Board Diagnostic systems are self-diagnostic systems incorporated into the computers of new vehicles. Nearly all 1996 and newer vehicles less than 14,000 lbs. (e.g., passenger cars, pickup trucks, sport utility vehicles) are equipped with OBD II systems, which are California's second generation of OBD requirements. The OBD II system monitors virtually every component that can affect the emission performance of the vehicle to ensure that the vehicle remains as clean as possible over its entire life, and assists repair technicians in diagnosing and fixing problems with the computerized engine controls. If a problem is detected, the OBD II system illuminates a warning lamp on the vehicle instrument panel to alert the driver. This warning lamp typically contains the phrase Check Engine or Service Engine Soon (see below). The system will also store important information about the detected malfunction so that a repair technician can accurately find and fix the problem. CARB has also developed similar OBD requirements (heavy-duty OBD or HD OBD)  for heavy-duty vehicles over 14,000 lbs.

Check Engine Lights

Below are links to further information regarding OBD, including the latest regulations and reports.

Most Recent Updates:

January 14, 2019: Minor revisions made to the HD OBD diesel rate-based data report template on the OBD Updates page.

October 25, 2018: Revisions made to the OBD II and HD OBD rate-based data report templates on the OBD Updates page.

September 27, 2018: HD OBD and OBD II 45-Day Notice Package (Board Hearing date: November 15-16, 2018) posted on the Heavy-Duty OBD Regulations and Rulemaking page.

Consumer Information on OBD II:

Facts Sheet: Frequently asked questions (FAQs) about OBD II and how it works.
U.S. EPA OBD II site: The United States Environmental Protection Agency's (U.S. EPA) website also includes consumer information about the OBD II system.

OBD II Regulations and Rulemaking Information:

OBD II Regulations and Rulemaking: Links to CARB's current/most recent OBD II rulemaking activities.
Past OBD II Regulatory Documents: Links to past OBD II regulations and rulemaking activities.

HD OBD Regulations and Rulemaking Information:

In 2004, CARB adopted a regulation requiring diagnostic systems on all 2007 and subsequent model year heavy-duty engines and vehicles (i.e., vehicles with a gross vehicle weight rating greater than 14,000 lbs.) in California. CARB subsequently adopted a comprehensive OBD regulation for 2010 and subsequent model year heavy-duty vehicles.

Heavy Duty OBD Regulations and Rulemaking: Links to CARB's current/most recent rulemaking activities.
Past Heavy-Duty OBD Regulatory Documents: Links to past HD OBD regulations and rulemaking activities.
U.S. EPA Heavy Duty OBD Site: U.S. EPA's website containing its heavy-duty requirements and other information.
Innovative Technology Regulation: Link to CARB's regulatory work regarding certification (including OBD certification) and aftermarket part approval flexibility for "innovative" medium- and heavy-duty engine and vehicle technologies.

Other OBD Information:

OBD Updates: Links to other OBD-related information, including Mail-Outs and ARB presentations from conferences.
OBD Workshops and Meetings: Links to all OBD-related workshops/meetings information.
Weber State Clearinghouse: Website containing information aimed at helping technicians (I/M and repair technicians) address problem vehicles.

OBD II-I/M Program Information:

CARB has worked with U.S. EPA to develop national guidelines for the implementation of OBD II into the Inspection and Maintenance (I/M) program. CARB has also worked with the Bureau of Automotive Repair (BAR), which is part of the California Department of Consumer Affairs, in its incorporation of OBD II into the California Smog Check program, which is administered by BAR.

U.S. EPA OBD II-I/M Site: U.S. EPA website containing the latest reports and information on the incorporation of OBD II into the I/M program.
BAR Smog Check Site: BAR's Smog Check website containing details regarding the use of OBD II in its Smog Check program.

E-Mail Updates for OBD:

OBD List Serve: Sign up here for e-mail updates regarding CARB's activities concerning OBD.


For more information, please contact Mike Regenfuss at (626) 575-7004.