Fail Safe Operation

PURPOSE
The fail-safe system makes engine starting possible if there is something malfunctioning in the Engine Control Module's (ECM) Central Processing Unit (CPU) circuit.
When the fail-safe system activates, the Malfunction Indicator Lamp comes on to warn the driver that a malfunction has occurred.

OPERATION

Engine Control With ECM Malfunction:

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

Mass Air Flow Sensor Malfunction:

MASS AIR FLOW SENSOR MALFUNCTION
If the ECM senses that the Mass Air Flow Sensor (MAFS) output voltage is out of the normal range it will substitute the Throttle Position Sensor signal for the correct signal. Engine RPM will be limited to 2400 in order to inform the driver that the ECM is in the "Fail-Safe Mode". Refer to the figure for operating conditions.

Engine Coolant Temperature Sensor Malfunction:

ENGINE COOLANT TEMPERATURE SENSOR MALFUNCTION
When the ECM 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 POSITION SENSOR MALFUNCTION
When the ECM 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.