On Board Diagnostic System

Fig. 12 On-Board Diagnostic Fault Code Index:

The On-Board diagnostic system is a built in function of the electronic control unit. The ECU constantly monitors all input and output functions and compares the various readings against a programmed set of standard values. When the reading from a component is significantly out of the 'normal' range, the ECU will illuminate the "CHECK ENGINE" light in the instrument cluster to notify the driver that a problem exists.
When it has been reported that the "CHECK ENGINE" light has come on, turn the ignition ON, pull down the passenger's side carpet inspection flap from under the dashboardand observe the LED on the top of the ECU. The LED indicates a system failure code by its blinking. This code can help to locate and repair failed components in the fuel injection or emission control systems.