Interior Lighting

The interior lighting system consists of the following:
^ dome/map lamp
^ rear dome/cargo lamp
^ overhead console/map lamp
^ RH/LH vanity mirror
^ ash receptacle lamp
^ puddle lamps
^ interior lamp switches
^ interior lamp relay
^ dimmer module
^ battery saver relay
^ Generic Electronic Module (GEM)

Generic Electronic Module (GEM)/Central Timer Module (CTM) Controlled Functions
The generic electronic module (GEM) is equipped on four-wheel drive vehicles with power windows. The Central Timer Module (CTM) is equipped only on two-wheel drive vehicles without power windows.

NOTE: GEM/CTM diagnostics are compatible with the scan tool.

The GEM/CTM 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/CTM constantly monitors the systems it controls and reports a concern in the form of a Diagnostic Trouble Code (DTC). A DTC can be retrieved with the scan tool through the communication link.

The scan tool is a menu-driven tester that allows the user to run specific tests. The scan tool can isolate faults in the GEM/CTM subsystems through a symptom-driven diagnostic procedure. Connecting the scan tool to the GEM/CTM communication link will not alert the GEM/CTM. If the GEM/CTM is "asleep" when the diagnostic connector is plugged in, the GEM/CTM must be "awakened". If the communication link cannot be established, turn the ignition to RUN.

NOTE: The OEM/CTM has a sleep function to minimize battery consumption. During the sleep mode, the GEM/CTM turns off all outputs and monitors only the following:
^ door ajar (driver door, passenger door, liftgate, LH rear and RH rear doors).
^ key-in-ignition.
^ key in RUN or ACC.
^ two-step unlock switch (unarm switch).
^ digital TR sensor.
^ illuminated entry request (Remote Anti-theft Personality [RAP] module).

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

The GEM/CTM 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/CTM control system has two modes of operation; the normal operating mode and the tester-dependent diagnostics mode.

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

NOTE: The GEM/CTM can only detect open circuit/short to GRD faults when the GEM/CTM is not energizing a load, and short to battery faults when the GEM/CTM is attempting to energize a load.
^ GEM/CTM continuous self-test (RAM, ROM, EEPROM, A/D checking).
^ output driver monitoring (open circuit/short to ground [GRD], short to power).
^ illogical combinations of input signals.

Interior Lighting-Features

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

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

The battery saver feature removes extended interior lamp power drains to the battery. The GEM/CTM maintains power to these loads for 45 minutes after the ignition switch is turned to OFF. After the ignition switch is turned to OFF and 45 minutes have elapsed with no change of state on any wake-up inputs, the GEM/CTM will enter "sleep mode." During sleep mode, the GEM/CTM 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 GEM receives an illuminated entry request.
^ the key is inserted into or removed from the ignition.
^ 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.

The GEM/CTM illuminates the interior courtesy lamps when any door is set ajar or is opened. The following are inputs used for controlling the courtesy lamps:
^ all door ajar switches (including liftgate and liftgate glass).
^ illuminated entry request (RAP module).
^ vehicle speed signal input (GEM only).

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) (GEM only).
^ a power door lock command is received before the five seconds have elapsed for two-step unlock.

The GEM/CTM 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.

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

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 1013 (BR/LG) is normally sent 12 volts by the GEM. The RAP module shorts this circuit to ground with a pulse of either of the following lengths:
^ 200 ms pulse from RAP receiver assembly request illuminated entry ON.
^ 300 ms pulse from RAP receiver assembly request illuminated entry OFF.

The illuminated entry feature (GEM only) is another feature which activates the interior lamps. This feature operates as follows:
The GEM illuminates the interior lamps when an unlock signal is received from the RAP module. The illuminated entry feature will be canceled when any of the following 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 the ignition switch in the key-in, ACC and RUN positions, and the illuminated entry request (RAP module).

There are no GEM sleep mode outputs; all circuits are deactivated during sleep mode.

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