TABLE D-6 Timetable for Implementation of On-Board Diagnostic (OBD) II Systems for Heavy-Duty Vehicles (more than 14,000 lb GVWR)

Regulatory Body

Model Year


California Air Resources Board (CARB)


Basic Engine Manufacturer Diagnostic (EMD) system


2010 Proposed

Comprehensive OBD II system

U.S. Environmental Protection Agency

2010 Proposed

Notice of Proposed Rule

standards become more stringent in recent years. The most stringent evaporative emission standards have recently been introduced for gasoline-fueled vehicles. California currently has an optional zero evaporative emission standard, which is one of the requirements for certifying a vehicle with SULEV exhaust emissions as a partial zero emission vehicle.

In recognition of the high temperatures that diesel fuel can reach in modern common rail fuel systems, evaporative emission standards for diesel fuel vehicles have also been adopted. Because technology to control diesel evaporative emissions are not considered to be a significant issue, these emissions are not included in the scope of 21CTP and will not be discussed in this report.

On-Board Diagnostic II (OBD II) System

The On-Board Diagnostic II (OBD II) system was phased in on light-duty vehicles beginning with the 1994 model year vehicles. The purpose of the on-board diagnostic system on vehicles is to ensure the emission control system and other engine-related components are operating properly. When the OBD II system detects a problem, a corresponding “Diagnostic Trouble Code” (DTC) is stored in the computer’s memory and a special light on the instrument cluster called a Malfunction Indicator Lamp (MIL) is illuminated.

The OBD II system is intended to ensure proper emission system operation for every vehicle throughout its lifetime, and notifies the driver of a problem before the vehicle’s emissions have increased significantly.

Heavy-duty engine OBD II, also referred to as the engine manufacturer diagnostic system, is similar to the light duty OBD II system, except that the monitors are not required to be tied to the emission standards (Dieselnet, 2005; EPA, 2006).

The timetable for implementation of OBD II for heavy-duty vehicles as shown in Table D-6.

Although OBD II is a key element in maintaining the stringent emission levels that are the focus of the 21CTP, the development and application of OBD II are not included in the scope of this partnership and are not discussed further in this report.

Defeat Devices

Manufacturers must ensure that vehicle emission control systems operate in use as they do on the prescribed test cycles. If, without properly informing EPA, an emission control system operates differently when in use, the emission control system is considered “defeated” and a “defeat device” is present. EPA may seek judicial penalties for each vehicle sold containing a defeat device (EPA, 2007a).


Dieselnet. 2005. California adopts OBD requirements for heavy-duty engines. July 22. Available at Accessed May 29, 2007.

DOE (U.S. Department of Energy). 2006. 21st Century Truck Partnership Roadmap and Technical White Papers. Doc. No. 21CTP-003. Washington, D.C. December.

Ehlmann, James, and George Wolff. 2005. Automobile Emissions—The Road Toward Zero. Air and Waste Management Association. January.

EPA (U.S. Environmental Protection Agency). 1994. Fact Sheet OMS-12, August.

EPA. 2006. Regulatory Announcement: Proposed Rule on OBD for Heavy Duty Engines. EPA 420-F-06-058. Washington, D.C.: Office of Transportation and Air Quality. April.

EPA. 2007a. Clean Air Act Enforcement. Available at Accessed September 7, 2007.

EPA. 2007b. Green Book [Non-attainment Areas under the Clean Air Act of 1972 as Amended]. Available at Accessed June 14, 2007.

Johnson, J. H. 1988. Automotive Emissions. P. 45 in Air Pollution, the Automobile, and Public Health. Washington, D.C.: National Academy Press.

The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement