Description of On-Board Diagnostics

Electronic Control System

The functions of the fuel and emission control systems are managed by the powertrain control module (PCM).

Fail-safe Function
When an abnormality occurs in a signal from a sensor, the PCM 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 PCM, the injectors are controlled by a back-up circuit independent of the system in order to permit minimal driving.

Self-diagnosis
When an abnormality occurs in the signal from a sensor, the PCM 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 PCM supplies ground to the MIL for 15 to 20 seconds on '01-03 models (2 seconds on '99-00 models) 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 PCM stores it in its memory. When the same abnormality recurs after the ignition switch is turned OFF and ON (II) again, the PCM informs the driver by turning on the MIL.