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 PCM 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 PCM 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 PCM supplies ground for the MIL and stores the DTC in erasable memory. When the ignition is initially turned on, the PCM supplies ground for the MIL for two seconds to check the MIL bulb condition.

4. Two Trip Detection Method ('96 - 97 models)
To prevent false indications, the Two Trip Detection Method is used for the HO2S, fuel metering-related, idle control system, ECT sensor, EGR system self-diagnostic functions and EVAP control system. 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 lighting the MIL.
However, to ease troubleshooting, this function is cancelled when you short the service check connector. The MIL will then blink immediately when an abnormality occurs.

5. Two Driving Cycle Detection Method ('96 - 97 models)
A "Driving Cycle" consists of starting the engine, beginning closed loop operation, and stopping the engine. If misfiring that increases emissions, EVAP control system malfunction or TWC deterioration is detected during two consecutive driving cycles, the PCM turns the MIL on.
However, to ease troubleshooting, this function is cancelled when you short the service check connector. The MIL will then blink immediately when an abnormality occurs.

6. Two Driving Cycle Detection Method ('98 - 00 models)
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 and EVAP control system and other self-diagnostic functions. When an abnormality occurs, the PCM stores it in its memory. When the same abnormality recurs after switch is turned OFF and ON (II) again, the PCM informs the driver by turning on the MIL.