Interior Lighting

Generic Electronic Module (GEM) Controlled Functions
The Generic Electronic Module (GEM) is equipped on four-wheel drive vehicles with power windows. The Central Timing Modules (CTMs) are equipped only on the two-wheel drive vehicles without power windows.

NOTE: GEM diagnostics are compatible with the New Generation STAR (NGS) Tester. 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 Codes (DTCs). A DTC can be retrieved with the NGS Tester through the communication link.

The NGS is a menu-driven tester, allowing the user to run specific 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 door, passenger door, lift gate, left rear, and right rear doors).
Key-in-ignition.
^ Key in RUN or ACC.
^ Door handles (driver or passenger).
^ Two-step unlock switch (unarm switch).
^ Neutral safety switch.
^ Illuminated entry request (Remote Anti-theft Personality [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 in any wake-up input.

The GEM control system has two modes of operation, the normal operating mode and the 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 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 ground [GRD], short to power).

NOTE: The GEM can only detect open circuit/short to GRD faults when the GEM in not energizing a load, and short to battery faults when the GEM is attempting to energize a load.

^ Illogical combinations of input signals.

Battery Saver

NOTE: The exterior lamps are not part of the battery saver protection, and will remain on even if the GEM turns the interior lamps off.

The GEM will keep power available for all interior lights including: dome lamp, map lamp, glove box lamp, ash tray lamp, key ring lights and cargo lamp circuits for 45 minutes after the ignition switch is turned off. The battery saver time is reset by lifting a door handle (receiving an illuminated entry request), activating a door ajar switch, changing the ignition to START, or moving the key to the RUN or ACC position.

The battery saver feature removes extended interior lamp power drains to the battery. The GEM keep power to these loads for 45 minutes after the ignition switch is moved to OFF. After the ignition switch is moved to OFF and 45 minutes have elapsed with no change of state on any wake-up inputs, the GEM will enter a "sleep mode." During the sleep mode, the GEM maintains all of its outputs in a deactivated state until a wake-up-command is received.

A wake-up-command is sent when:
^ Any door becomes ajar or is opened or closed.
^ The front door handle is lifted (if equipped with illuminated entry).
^ The key is inserted or removed.
^ The ignition switch is turned from OFF to RUN.
^ The ignition switch is turned from OFF to ACC.
^ A wake up request is received from the RAP module.

Courtesy Lamps
The GEM illuminates the interior courtesy lamps when any door is set ajar or is opened. These are the inputs used for controlling the courtesy lamps:
^ All door ajar switches (including liftgate).
^ Door handle switches.
^ Illuminated entry request with RAP module.
^ Two-step unlock door disarm switches.
^ Vehicle speed sensor input.

All interior courtesy lamps are turned off when any of the following occurs:
^ All the doors are closed and the illuminated entry feature is not active.
^ The ignition switch is turned to RUN.
^ Vehicle speed is over 8 km/h (5 mph).
^ A power door lock command is received before the five seconds have elapsed for two-step unlock.

Interior Lamp Relay
The GEM controls the interior lamps illuminated entry function with the interior lamp relay. The relay is activated by applying ground to the relay coil through C283-12, and is deactivated by removing the ground.

Panel Dimmer Switch
The panel dimmer switch controls the interior lamps by supplying power to the interior lights. The battery saver relay supplies power to the panel dimmer switch. When the battery saver function is active, power will not be supplied to the dimmer switch circuit and the panel dimmer switch will not turn on the interior lighting.

Remote Anti-Theft Personality Module
The RAP module sends a signal to the GEM on the illuminated entry request circuit to indicate a request to turn the illuminated entry feature ON or OFF. Circuit 101 3(BR/LG) is normally sent to 12 volts by the GEM. The RAP module shorts this circuit to ground with a pulse of either of the lengths:
^ 200 ms pulse from RAP receiver assembly request illuminated entry ON.
^ 300ms pulse from RAP receiver assembly request illuminated entry OFF.

Illuminated Entry
The illuminated entry feature is another feature which activates the interior lamps. This feature works as follows:

The GEM illuminates the interior lamps when either front door handle is lifted or an unlock signal is received from the RAP module. The illuminated entry feature will be canceled when any of the these conditions are met:
^ 25 seconds have elapsed since the illuminated entry feature was activated and the interior lamp control is not activated.
^ The GEM receives a request from the RAP module (remote transmitter lock button pressed) and the courtesy lamp control is not activated.
^ The ignition is in the RUN or START position and the interior lamp control is not activated.

The illuminated entry inputs are:
^ Door Open warning switch (grounded when the handle is lifted; an open circuit when the handle is released).
^ Ignition switch in the key-in, ACC and RUN position.
^ RAP illuminated entry request.

The GEM sleep mode outputs are:
^ NONE. (All circuits are deactivated during sleep mode).

If a change in any of the inputs occurs while the GEM is asleep, the GEM will wake up and monitor all of its inputs and have the ability to activate any of its outputs.