Engine Control Module: Description and Operation

ECM Fail-safe/Back-up Functions
1. 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.

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

3. Self-diagnosis Function [Malfunction Indicator Lamp (MIL)]
When an abnormality occurs in a signal from a sensor, the ECM supplies ground for the MIL and stores the DTC in erasable memory. When the ignition is initially turned on, the ECM supplies ground for the MIL for two seconds to check the MIL bulb condition.

4. Two Driving Cycle Detection Method
To prevent false indications, the two driving cycle detection method is used for the HO2S, 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 stores it in its memory. When the same abnormality recurs after the ignition switch is turned OFF and ON (II) again, the ECM informs the driver by lighting the MIL. However, to ease troubleshooting, this function is cancelled when you jump the service check connector. The MIL will then blink immediately when an abnormality occurs.