Description of On-Board Diagnostics

DESCRIPTION

The fail-safe system makes engine starting possible if there is something malfunctioning in the Engine Control Module (ECM)'s Central Processing Unit (CPU) circuit.

OPERATION
Fail-safe system activating condition when ECM is malfunctioning
The fail-safe mode operates 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 with fail-safe system, operates when ECM is malfunctioning When the fail-safe system is operating, fuel injection, ignition timing, fuel pump operation, Idle Air Control Valve (IACV-AAC) valve operation, and so on are controlled under certain limitations.

Fuel injection Simultaneous multiport fuel injection system
Ignition timing Ignition timing preset value is fixed at the factory Ignition timing .
Fuel pump Fuel pump relay is "0N" when engine is running and "0FF" when engine stalls.
IACV-AAC valve Full open
cooling fans cooling fan relays "0N"

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 Fail Safe Operation:

MASS AIR FLOW SENSOR MALFUNCTION
if the mass air flow sensor output voltage is below the specified value, the ECM senses an mass air flow sensor malfunction. in the 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, water temperature is fixed at the preset value as follows:

Condition Engine coolant temperature determined by ECM
Just as ignition switch 40 (104°F)
is turned ON or START

More than 6 minutes after 80°c (176°F)
ignition ON or Start

Except as shown above 40 - 80°c (104 - 176°F)
(Depends on the time)

KNOCK SENSOR MALFUNCTION
When the output signal of the knock sensor is abnormal, the ECM judges it to be malfunctioning. When the knock sensor is malfunctioning, ignition timing will retard according to operating conditions.

THROTTLE POSITION SENSOR MALFUNCTION
Description
When the output signal of throttle position sensor is abnormal the ECM judges it as a closed throttle position sensor malfunction.

With throttle position switch The ECM does not use the throttle position sensor signal, but determines the idle position by the closed throttle position switch.

Operation Driving condition
when engine is idling Normal
when accelerating Poor acceleration