Description of On-Board Diagnostics

Fail Safe Input/output:

DESCRIPTION
The fail-safe system makes engine starting possible if there is something malfunctioning in the Engine Control Module (ECM)'s CPU circuit, or if there is a disconnection or short/open circuit in the camshaft position sensor circuit. In former models, engine starting was difficult under the conditions mentioned above. But with the provisions provided 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 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, 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.

Fail-safe system activating condition when camshaft position sensor is malfunctioning
The fail-safe mode operation starts immediately after all of the following conditions have been satisfied for several seconds.
1. No pulse of 120 signal (reference signal) detected for several seconds, or 1 signal (position signal) is equivalent to 0 rpm.
2. Ignition switch in START
3. Battery voltage is greater than 10 volts with ignition switch ON.
4. The neutral position switch is ON, or the inhibitor switch is in the "P" or "N" position.
5. When ignition switch is in START, battery voltage is at least 1 volt lower than when ignition switch is ON.

When the camshaft position sensor fail-safe system activates, the MALFUNCTION INDICATOR LAMP on the instrument panel lights to warn the driver.


Engine control with fail-safe system when camshaft position sensor is malfunctioning
When the fail-safe system is operating, fuel injection, ignition timing, fuel pump operation, engine idle speed, Exhaust Gas Recirculation (EGR) operation, cooling fan operation, and power valve operation are controlled under certain limitations.


Cancellation of fail-safe system when camshaft position sensor 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 above-mentioned activating conditions are satisfied after turning the ignition switch from OFF to ON.

Mass Air Flow Sensor Malfunction:

MASS AIR FLOW SENSOR MALFUNCTION
If the mass air flow sensor output voltage is above or below the specified value, the ECM senses a mass air flow sensor malfunction. In case of a malfunction, the throttle position sensor substitutes for the mass air flow sensor.

Though mass air flow sensor is malfunctioning, it is possible to drive the vehicle and start the engine. But engine speed will not rise more than 2,000 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 is fixed at the preset value as follows:


Condition Engine coolant temperature decided
Just as ignition switch 20°C (68°F)
is turned ON or Start.
More than 6 minutes after 80°C (176°F)
ignition ON or Start.
Except as shown above. 80°C (176°F)
(depends on the time)

FUEL PUMP MALFUNCTION
When the ECM detects a malfunction (discontinuity, short-circuit, etc.) in the fuel pump voltage control circuit, the fuel pump relay turns ON and 12 volts are applied to the fuel pump.


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 according to operating conditions.