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 the signal from a sensor, the ECM ignores that signal and assumes a pre-programmed value for that sensor the 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 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 to the MIL for 15 to 20 seconds to check the MIL bulb condition. If all readiness codes are not set, the MIL will flash five times If readiness codes are set to complete, the MIL will go out. The MIL may be turned off by the ECM if the problem that originally caused the MIL to be illuminated was an intermittent problem.

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)