Check engine lights come on when there’s a problem in your car’s system. Modern car systems have On-board Diagnostics II (OBD-II). This is a standardized system designed for testing stations to use one machine for all cars from 1996 until today.
For vehicles before 1996 we use different techniques and two different online information systems to access the diagnostic information you would normally receive from a dealership. Most Asian and American models fit the criteria for these systems.