Gem Controlled Functions: Notes

The Generic Electronic Module (GEM) incorporates the functions of several different modules into one and offers diagnostics to easily locate and repair concerns affecting the subsystems that it controls. See Fig 1.

The GEM constantly monitors the system and reports concerns in the form of Diagnostic Trouble Codes (DTCs). The DTCs can be retrieved with the Rotunda New Generation Star (NGS) Tester 007-00500 or equivalent through the communication link.

The NGS is a menu-driven tester, allowing the user to run specific diagnostic tests. The NGS can isolate faults in the GEM subsystems through a symptom-driven diagnostic procedure. Connecting the tester to the GEM communication link will NOT alert the GEM. If the GEM is "asleep" when the diagnostic connector is plugged in, the GEM must be "awakened." If the communication link cannot be established, it is advised to turn the ignition to RUN.

NOTE: The GEM has a sleep function to minimize battery consumption. During the sleep mode, the GEM turns off all outputs and monitors only the following:

Door ajar (driver's door, passenger's door, liftgate, rear right and rear left doors).
Key in ignition.
Key in RUN or ACCY position.
Door handles (driver's or passenger's).
Two-step unlock switch.
Neutral safety switch.
Illuminated entry request-RAP module.

If a change of status occurs at one of these inputs while the GEM is asleep, the GEM will "wake up". When the GEM awakens, it performs an internal self test, and begins normal operation. At this point, the GEM will have all of its functions operational.

The GEM will go into the sleep mode immediately after both of the following conditions have been met.

Key in OFF or key not in ignition.
After 45 minutes with no change on any wake-up input.

The GEM control system has two modes of operation, the normal operating mode and tester dependent diagnostics mode.

The normal operation of the GEM can detect errors. An integral part of the normal GEM operation is the continuous diagnostics capability. Continuous diagnostics detects errors and changes the GEM control strategy. There is no warning light for the GEM; therefore, a DTC concern will direct you to the GEM. Examples of faults that may be detected during normal operation include

GEM continuous self test (RAM, ROM, EEPROM, A/D checking).
Output driver monitoring (open circuit/short to GND, short to battery).
NOTE: The GEM can only detect open circuit/short to GND faults when the GEM is not energizing a load, and short to battery faults when the GEM is attempting to energize a load.
Illogical combinations of input signals.

A description of the subsystems controlled by the GEM follows.

Fig 1: View Of Generic Electronic Module (GEM)

Courtesy of FORD MOTOR CO.