California on-board diagnostic (OBD) requirements for light-duty vehicles and for heavy-duty engines used in vehicles below 14,000 lbs GVWR have been introduced in two steps:
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- OBD I—The first OBD regulation in the United States, which required manufacturers to monitor some of the emission control components on all 1991 and newer vehicles sold in California.
- OBD II—This more rigorous OBD regulation started to be phased-in in 1994. Since 1996, it has been required for all new gasoline and alternate fuel passenger cars and trucks sold in California. All 1997 and newer diesel fueled passenger cars and trucks are also required to meet OBD requirements.
The OBD I systems were limited to monitoring only a few of the emission-related components and they were not calibrated to a specific level of emission performance. OBD II systems were developed to address these shortcomings, and make the system more user-friendly for service technicians. On-board diagnostic capabilities with OBD II systems are incorporated into the hardware and software of a vehicle’s on-board computer to monitor every component that can affect emission performance. Each component is checked by a diagnostic routine to verify that it is functioning properly. If a problem or malfunction is detected, the OBD II system illuminates a warning light on the vehicle instrument panel to alert the driver. This warning light will typically display the phrase “Check Engine” or “Service Engine Soon”. The system will also store important information about the detected malfunction so that a repair technician can accurately find and fix the problem.
California on-board diagnostic requirements for heavy-duty engines for vehicles with a GVWR greater than 14,000 lb have also been introduced in two stages, as follows:
- EMD—Starting in the 2007 model year, heavy-duty engines require a very basic diagnostic system referred to as Engine Manufacturer Diagnostic (EMD) system.
- OBD—Starting in 2010, OBD requirements for heavy-duty engines will start to be phased-in. By 2013, EMD systems will be phased out and all heavy-duty engines offered for sale in California will also require OBD systems.