Description of On-Board Diagnostics

Electronic Control System

The functions of the fuel and emission control systems are managed by the Engine Control Module (ECM).

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.

Back-up Function
When an abnormality occurs in the ECM itself, the fuel injectors are controlled by a back-up circuit in the ECM in order to permit minimal driving.

Self-diagnosis
When an abnormality occurs in the signal from a sensor, the ECM supplies ground for the Malfunction Indicator Lamp (MIL) and stores the Diagnostic Trouble Code (DTC) in erasable memory. When the ignition is first turned on, the ECM supplies ground for the MIL for 15 - 20 seconds to check the MIL bulb condition.

Two Driving Cycle Detection Method
To prevent false indications, the "two driving cycle detection method" is used for the fuel metering-related components, idle control system, ECT sensor, TWC, EGR system, EVAP control system and other self-diagnostic functions. When an abnormality occurs, the ECM stores it in its memory. When the same abnormality recurs after the ignition switch is turned OFF and ON (II) again, the ECM informs the driver by turning on the MIL.