Failure Mode Effects Management (Fmem); Hardware Limited Operation Strategy (Hlos); Malfunction Indicator Lamp (Mil); Diagnostic Connector - Ford Ranger Maintaince And Repair Manual

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FAILURE MODE EFFECTS MANAGEMENT (FMEM)

The engine controller assembly contains back−up programs which allow the engine to operate if a sensor

signal is lost. If a sensor input is seen to be out of range−either high or low−the FMEM program is used. The

processor substitutes a fixed value for the missing sensor signal. The engine will continue to operate, although

performance and driveability may be noticeably reduced. This function of the controller is sometimes referred

to as the limp−in or fail−safe mode. If the missing sensor signal is restored, the FMEM system immediately

returns the system to normal operation. The dashboard warning lamp will be lit when FMEM is in effect.

This mode is only used if the fault is too extreme for the FMEM circuit to handle. In this mode, the processor

has ceased all computation and control; the entire system is run on fixed values. The vehicle may be operated

but performance and driveability will be greatly reduced. The fixed or default settings provide minimal

calibration, allowing the vehicle to be carefully driven in for service. The dashboard warning lamp will be lit

when HLOS is engaged. Codes cannot be read while the system is operating in this mode.

The CHECK ENGINE or SERVICE ENGINE SOON dashboard warning lamp is referred to as the

Malfunction Indicator Lamp (MIL). The lamp is connected to the engine control assembly and will alert the

driver to certain malfunctions within the EEC system. When the lamp is lit, the PCM has detected a fault and

stored an identity code in memory. The engine control system will usually enter either FMEM or HLOS mode

and driveability will be impaired.

The light will stay on as long as the fault causing it is present. Should the fault self−correct, the MIL will

extinguish but the stored code will remain in memory.

Under normal operating conditions, the MIL should light briefly when the ignition key is turned ON. As soon

as the PCM receives a signal that the engine is cranking, the lamp will be extinguished. The dash warning

lamp should remain out during the entire operating cycle.

To read Diagnostic Trouble Codes (DTC's) the test connector for the EEC system must be used. This

connector is known as the Assembly Line Diagnostic Link (ALDL) connector on vehicles with EEC−IV

ignition equipped engines, or the Data Link Connector (DLC) on all other models (EEC−V), is located in the

passenger compartment. It is attached either to the underside of the instrument panel, and is accessible from

the driver's side of the vehicle, or it is under the hood near the power distribution box.

The connector is trapezoidal in shape and can accommodate up to 16 terminals.

FAILURE MODE EFFECTS MANAGEMENT (FMEM)

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