On Board Diagnostic System

BACK-UP FUNCTION
When an abnormality occurs in the Engine Control Module (ECM) itself, the fuel injectors are controlled by a back-up circuit independent of the system in order to permit minimal driving.

FAIL-SAFE FUNCTION
When an abnormality occurs in a signal from a sensor, the ECM ignores that signal and assumes a pre-programmed value for that sensor that allows the engine to continue to run.

SELF-DIAGNOSIS FUNCTION/MALFUNCTION INDICATOR LAMP (MIL)
When an abnormality occurs in a signal from a sensor, the ECM lights the MIL and stores the Diagnostic Trouble Code (DTC) in erasable memory. When the ignition is initially turned in, the ECM supplies ground for the MIL for two seconds to check the MIL bulb condition.

TWO TRIP DETECTION METHOD
To prevent false indications, the Two Trip Detection Method is used for the Heated Oxygen Sensor, fuel metering related, and Exhaust Gas Recirculation system self-diagnostic functions. When an abnormality occurs, the ECM stores it in its memory. When the same abnormality reoccurs during the next driving cycle, the ECM informs the driver by lighting the MIL. For troubleshooting purposes, the Two Trip Detection can be cancelled by shorting the Service Check Connector. The MIL will then blink immediately when an abnormality occurs.