GEM Controlled Functions

The Generic Electronic Module (GEM) is equipped on four wheel drive vehicles with power windows. The Central Timing Module (CTM) is equipped only on the two wheel drive vehicles without power windows.

NOTE: GEM diagnostics are compatible with the New Generation STAR (NGS) Tester while CTM diagnostics are not.

The 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.

The GEM constantly monitors the systems under its control and reports a concern in the form of Diagnostic Trouble Code (DTC). A DTC can be retrieved with the NGS or equivalent through the communication link.

The NGS is a menu-driven tester, allowing the user to run specific diagnostic tests. It 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 in sleep mode when the diagnostic connector is plugged in, the GEM must be activated. If the communication link cannot be established, it will advise 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 door, passenger door, lift gate, left rear, and right rear doors).
^ Key in ignition.
^ Key in RUN or ACCY.
^ Door handles (driver or passenger).
^ Two-step unlock switch (disarm switch).
^ Neutral safety switch.
^ Illuminated entry request (RAP module).

If a change of status occurs at one of these inputs while the GEM is in sleep mode, the GEM will activate. When the GEM activates, 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 sleep mode immediately after both of the following conditions have been met:
^ Key in OFF position.
^ After 45 minutes with no change on any activation 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 diagnostic 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 the technician 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).
^ Illogical combinations of input signals.

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.