Description of On-Board Diagnostics

The ECU will substitute the input signals for the air flow meter, throttle sensor, ECU and water temperature sensor if the circuits fail. This will allow the vehicle to driven until repairs can be made.
NOTE: The engine will operate at reduced capacity.

C.P.U. MALFUNCTION OF E.C.U.
The fail-safe system makes it possible to start the engine when a malfunction is detected in the E.C.U.'s C.P.U. circuit. In previous model years, starting was difficult under the above conditions. The fail-safe system now used makes starting is possible. When a malfunction is detected, the "Check Engine Light" comes on to warn the driver that a malfunction has occurred.

Engine Control With ECM Malfunction:

ENGINE CONTROL DURING ECU MALFUNCTION
Refer to Image for conditions and controls.

Air Flow Meter Malfunction:

AIR FLOW METER MALFUNCTION
If the ECU senses that the air flow meter output voltage is out of the normal range it will substitute the throttle sensor signal for the correct signal. Engine RPM will be limited to 2400 in order to inform the driver that the ECU is in the "Fail-Safe Mode". Refer to the figure for operating conditions.

Water Temperature Sensor Malfunction:

WATER TEMPERATURE SENSOR MALFUNCTION
When the ECU senses that the engine temperature output voltage is out of the normal range, it will substitute voltage at preset values. Refer to the figure for operating conditions.

Throttle Position Sensor Malfunction:

THROTTLE SENSOR MALFUNCTION
When the ECU senses that the throttle sensor is out of range it judges it as a malfunction.
The throttle sensor signal is not used, instead the idle position is calculated by the amount of fuel injected and the engine RPM.