California Air Resources Board

On-Board Diagnostic (OBD) systems are self-diagnostic systems incorporated into the computers of vehicles. The OBD 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.  If a problem with an emissions-related component is detected, the OBD system illuminates a warning lamp on the vehicle instrumental panel to alert the driver.  The system will also store important information about the detected malfunction so that a repair technician can accurately find and fix the problem.
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