On Board Diagnostics ...

Below is a quote from the "Wisconsin Natural Resources" magazine explaining OBD ...

... Today's cars are factory-equipped with computer systems that have more intelligence than the spacecraft NASA sent to the moon. From 1986 to 1995, cars were equipped with first-generation on-board diagnostic (OBD-1) systems. Since 1996, cars have been equipped with second-generation OBD-2 systems. ...

... an OBD-2 system is a complex network of sensors and controllers that continually monitors operation and performance to keep your car running cleanly and efficiently. When the "check engine" or warning light (also called a MIL, or Malfunction Indicator Lamp) on your dashboard comes on, your car's central computer records an internal diagnostic trouble code, or DTC.

The DTC gives a properly trained technician a starting point to begin further testing to diagnose, pinpoint and repair the root cause of the malfunction. ...