Fail-Safe System

PURPOSE
The Fail-Safe System activates and enables limited engine operation when the Engine Control Module (ECM) detects a failure in the following components or their circuits.

- Central Processing unit (CPU) inside the ECM.
- Mass Air Flow Sensor (MAFS).
- Engine Coolant Temperature Sensor (ECTS).
- Throttle Position Sensor (TPS).
- Knock Sensor

CPU Malfunction In ECM Fail-Safe Input/Output Signal Line:

OPERATION
ECM/CPU Malfunction
The Fail-Safe mode activates when the computing function of the ECM is judged as malfunctioning. Fuel injection, ignition timing, fuel pump operation, engine idle speed, Exhaust Gas Recirculation (EGR) operation, etc.. operate within limited pre-programed parameters. The (Check Engine) Malfunction Indicator Lamp (MIL) remains on during fail-safe operation.

Cancelation of Fail-Safe Mode with Malfunctioning ECM
Fail-Safe is canceled each time the ignition switch is turned off. The system reactivates if all the activating conditions are satisfied as the ignition switch is turned on.

Mass Air Flow Sensor Fail-Safe Operation:

Mass Air Flow Sensor Malfunction (MAFS)
If the ECM senses that the MAFS output voltage is out of the normal range it will substitute the throttle sensor signal for the correct signal. Engine speed will be limited to 2400rpm and the (Check Engine) lamp (MIL) will illuminate in order to inform the driver that the ECM is in the "Fail-Safe Mode".


Engine Coolant Temperature Sensor (ECTS) Malfunction
When the ECM senses that the engine temperature output voltage is out of the normal range, it will substitute voltage at preset values as follows:
Starting ......... 40° C (104° F)
Running .......... 80° C (176° F)

Throttle Position Sensor (TPS) Malfunction
The ECM stops using the TPS input signal if the voltage falls out of the normal range. The Closed Throttle Position Switch (Hard Idle) signal is then substituted for use during the Fail-Safe operation mode.

Knock Sensor Malfunction
If the signal from the Knock Sensor falls out of normal range due to a component or circuit failure, the ECM stops using that input and will advance or retard ignition timing according to operating conditions only. (Regardless of engine ping or lack of power).