Description of On-Board Diagnostics

Fig. 69 Fail-Safe Operation:

CIRCUIT OPERATION
The ECU will substitute the input signals for the engine temperature sensor and the throttle sensor circuits if they fail. It will also substitute the voltage signal to the fuel pump circuit. This will allow the vehicle to driven until repairs can be made.
NOTE: The engine will operate at reduced capacity.

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 2000 in order to inform the driver that the ECU is in the "Fail-Safe Mode".

Fig. 68 Temperature Sensor Fail-Safe Operation:

ENGINE 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 Fig. #68 for operating conditions.

NOTE: The radiator fan will operate on HIGH speed if a faulty temperature sensor condition exists.

FUEL PUMP CIRCUIT MALFUNCTION
When the ECU senses that the output circuit to the fuel pump is open or shorted it will activate the fuel pump relay. This will supply battery voltage directly to the fuel pump.