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ORIGINS OF OBD
The origins of OBD began back in 1982 when the California Air Resources Board (CARB)
initiated regulations which would require all vehicles sold in California, starting in
1988, to have an on-board diagnostic system to detect emission failures. This system would
later be referred to as OBD-I.
OBD-I was a simple ECU system that monitored various sensors and applied corrections to a
map value based on engine conditions. This system revolutionized the auto repair industry
by making it easy to identify faulty components, however, it provided no insight into
the conditions that lead to the problem. Another drawback was non-existent standardization
between different makes and models of vehicles and the availability of affordable scan
tools for these proprietary systems.
With that in mind, the next generation OBD-II system was based on new standards starting
in 1994 with a complete phase-in for California vehicles by 1996. Now, all vehicles must
be OBD-II compliant and have a standardized 16-pin data link connector (DLC) with specific
pins assignments, standardized communication protocols, standardized diagnostic trouble
codes (DTC) and standardized terminology. Prior to 2008, five protocol types were in use;
J1850-PWM, J1850-VPW, ISO 9141, KWP2000 and CAN. Starting in 2008, all vehicles sold in the
US must now be CAN-BUS compliant.
Current OBD-II systems do more than just electrically check components for short or open
circuits, OBD-II monitors any component that can have an effect on emissions by comparing
the sensor output to an expected range. If malfunctioning or out-of-range, a diagnostic
code number is stored which can only be read using a Code Reader or Scan Tool. Not all errors will cause
the (MIL) "Malfunction Indicator Lamp" or "Check Engine Lamp" to illuminate. But if it does,
this is a cause of concern to identify the problem before costly damage can occur. Sometimes,
it can be something simple such as a loose or missing gas cap which caused an "Evaporative
Emission Control" error.