Description of On-Board Diagnostics

System Descriptions

Electronic Control System

The functions of the fuel and emissions control Systems are managed by the engine control module (ECM).

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

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

Self-diagnosis
When an abnormality occurs in the signal from a sensor, the ECM supplies ground for the MIL and stores the DTC in erasable memory. When the ignition is first turned ON (II), the ECM supplies ground for the MIL for 2 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 some 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 turns on the MIL.