In April 1985, the California Air Resources Board (CARB) approved On-Board Diagnostic system regulations, referred to as OBD. These regulations, which apply to almost all 1988 and newer cars and light trucks marketed in the State of California, require that the engine control module (ECM) monitor critical emission related components for proper operation and illuminate a malfunction indicator lamp (MIL) on the instrument panel when a malfunction is detected. The OBD system also provides for a system of Diagnostic Trouble Codes (DTC) and fault isolation logic charts in the repair manual, to assist technicians in determining the likely cause of engine control and emissions system malfunctions. The basic objectives of this regulation are twofold:
• To improve in-use emissions compliance by alerting the vehicle operator when a malfunction exists.
• To aid automobile repair technicians in identifying and repairing malfunctioning circuits in the emissions control system.
OBD self diagnosis applies to systems which are considered to be most likely to cause a significant increase in exhaust emissions if a malfunction occurs. Most notably, this includes:
• All major engine sensors
• The fuel metering system
• Exhaust gas recirculation (EGR) function
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