Fail Safe Operation

Fail-Safe System:

PURPOSE AND OPERATION
The fail-safe system makes engine starting possible if there is something malfunctioning in the Engine Control Unit's (ECM's) Central Processing Unit (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 Operations Chart:

FAIL-SAFE SYSTEM ACTIVATION WITH ECM MALFUNCTION

The fail-safe mode operation starts when the computing function of the ECM is judged to be malfunctioning.

When the fail-safe system activates, i.e. if a malfunction condition is detected in the CPU of the ECM, the MALFUNCTION INDICATOR LAMP on the instrument panel lights to warn the driver.


ENGINE CONTROL IN FAIL-SAFE WITH ECM MALFUNCTION
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 WITH ECM MALFUNCTION

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.

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:
Engine condition Engine coolant temperature preset value °C (°F)

Start: 20 (68)

Running: 80 (176)


FUEL TEMPERATURE SENSOR MALFUNCTION

When fuel temperature sensor output voltage is below or above the specified value, fuel temperature signal is fixed at the preset value as follows:
Engine condition Fuel temperature preset value °C (°F)

Start: 20 (68)

Running: 80 (176)