Fail-Safe System

INPUT/OUTPUT SIGNAL LINE

CPU MALFUNCTION OF ECM - OUTLINE
The fail-safe system makes engine starting possible if there is something malfunctioning in the ECM's CPU circuit. In general, engine starting was difficult under the previously mentioned conditions. But with the provisions in this fail-safe system, it is possible to start the engine.

Fail-safe system activating condition when ECM is malfunctioning
The fail-safe mode operation starts when the computing function of the ECM is judged to be malfunctioning. When the fail-safe system activates, the MALFUNCTION INDICATOR LAMP on the instrument panel lights to warn the driver. The system activates upon detection of a malfunction in the CPU of the ECM.

Engine control, with fail-safe system, operates when ECM is malfunctioning
When the fail-safe system is operating, fuel injection, ignition timing, fuel pump operation, engine idle speed, EGR operation, and so on are controlled under certain limitations.

Cancellation of fail-safe system when ECM is malfunctioning
Activation of the fail-safe system is canceled each time the ignition switch is turned OFF. The system is reactivated if all of the activating conditions are satisfied after turning the ignition switch from OFF to ON.

Mass Air Flow Sensor Malfunction
If the mass air flow sensor output voltage is above or below the specified value, the ECM senses an mass air flow sensor malfunction. In case of a malfunction, the throttle position sensor substitutes for the mass air flow sensor. Although the mass air flow sensor is malfunctioning, it is possible to start the engine and drive the vehicle. But engine speed will not rise more than 2,400 rpm in order to inform the driver of fail-safe system operation while driving.




OPERATION




Engine Coolant Temperature Sensor Malfunction
When engine coolant temperature sensor output voltage is below or above the specified value, engine coolant temperature signal is fixed at the preset value as follows:

Knock Sensor Malfunction
When the output signal of the knock sensor is abnormal, the ECM judges it to be malfunctioning. When knock sensor is malfunctioning ignition timing will retard or advance according to operating conditions.

Throttle Position Sensor Malfunction
When the output signal of throttle position sensor is abnormal, the ECM judges it as a malfunctioning of throttle position sensor. The ECM does not use the throttle position sensor signal but uses a closed throttle position switch signal.