Description of On-Board Diagnostics
Electronic Control SystemThe 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, 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 to the MIL for 15 to 20 seconds to check the MIL bulb condition. If all readiness code are not set, the MIL will flash five times. If all readiness codes are set to complete, the MIL will go out. If the MIL was on but then went out, the original problem may have been an intermittent one.
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.