Failure Mode Effects Management

Improvements to the 1986 EEC-IV system has been made to allow better vehicle driveability when one or more sensors fail. The basic improvement within the ECA is that each sensor now has an input operating range. The ECA monitors whether the sensor is within operating limits. When an out-of-limit condition occurs, the ECA: stores a diagnostic code in its memory and substitutes an in-limit signal.
By substituting an in-limit signal, an alternate system strategy comes into operation which allows the vehicle the continue operating. Prior to the 1986 electronic control systems, the vehicle may have stalled or may not have operated at all.
If the MAP sensor fails, the TP sensor information is used as an engine load indication. The following would occur in the EEC-IV system:
1. Inferred barometric pressure.
2. Inoperative adaptive fuel strategy.
3. Fixed idle speed.
4. Inoperative EGR.
5. Inoperative MPG fuel.
The sensors used are referred to as deadband sensors. This means that there is a maximum and minimum range to the ECA from a functioning sensor. If the ECA receives a signal that is out-of-range, it assumes that the sensor has failed. This causes the ECA to go into the FMEM mode (strategy).