System Operation

Electronic Control System
The functions of the fuel and emission control systems are managed by the engine control module (ECM) on vehicles with manual transmissions or the powertrain control module (PCM) on vehicles with automatic transmissions.

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

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

Self-diagnosis [Malfunction Indicator Lamp (MIL)]
When an abnormality occurs in the signal from a sensor, the ECM/PCM supplies ground for the MIL and stores the DTC in erasable memory. When the ignition is first turned on, the ECM/PCM supplies ground for the MIL for two 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, idle control system, ECT sensor, EGR system, TWC, EVAP control system and other self-diagnostic functions. When an abnormality occurs, the ECM/PCM stores it in its memory. When the same abnormality recurs after the ignition switch is turned OFF and ON (II) again, the ECM/PCM informs the driver by turning on the MIL.