Generic Electronic Module (GEM) / Central Timer Module (CTM)

GEM/CTM System Outline
- The GEM is equipped on vehicles with four-wheel drive or with power windows.
- The CTM is equipped on vehicles with two-wheel drive or without power windows.
- The GEM/CTM control system has two modes of operation:
- Normal mode.
- Diagnostic mode.
- When the GEM/CTM is not energizing a load, the GEM/CTM can only detect open circuit and short to ground faults.
- When energizing a load, the GEM/CTM can only detect short to power faults.

Normal Operating Mode
- The normal operation of the GEM/CTM can detect errors.
- An integral part of the normal GEM/CTM operation is the continuous diagnostic capability. Continuous diagnostics detects errors and changes the GEM/CTM control strategy.
- There is no warning light for the GEM/CTM; therefore, a DTC concern will direct the technician to the GEM/CTM.
- Examples of faults that may be detected during normal operation include:
- GEM/CTM continuous self-test.
- Output driver monitoring (open circuit/short to GND, short to power).
- Illogical combinations of input signals.

Wiper/Washer Subsystem
- The GEM/CTM controls five modes of operation for the wiper. These modes are active only when the ignition switch is in the RUN or ACC position.
- The GEM/CTM responds to the windshield wiper control commands by interpreting inputs from the multi-function switch.
- The GEM/CTM relay drivers control the wiper HI/LO relay, wiper PARK/RUN relay and the washer pump relay.

Warning Lights and Audible Warning Devices Subsystem
- The GEM/CTM controls all audible warning devices and warning lights.
- The GEM/CTM performs a prove out on all GEM/CTM-controlled indicator/warning bulbs (except the seat belt and door ajar indicator lights) by turning on the bulb for two seconds after the ignition is turned to run.

Battery Saver Subsystem
- The battery saver feature removes extended interior lamp power drains to the battery.
- The GEM/CTM will keep power available for all interior lights for 45 minutes after the ignition switch is turned OFF.
- The battery saver is reset by:
- Receiving an illuminated entry request.
- Activating a door ajar warning switch.
- Starting the vehicle.
- Turning the ignition to RUN or ACC.

Interior Lamp Subsystem
- The GEM/CTM illuminates the interior courtesy lamps when any door is set ajar or is opened.
- All interior courtesy lamps are turned off when any of the following occurs:
- All doors are closed and illuminated entry feature is not active.
- The ignition switch is turned to RUN.
- Vehicle speed is over 5 mph (8 kmh mph).

Illuminated Entry Subsystem
- The illuminated entry feature (GEM only) activates the interior lamps.
- The GEM illuminates the interior lamps when an unlock signal is received from the RAP module.
- Illuminated entry inputs are:
- RAP illuminated entry request (grounded pulse of varying length).
- Ignition in RUN (battery voltage on both the RUN and RUN/ACC inputs).
- Illuminated entry output is:
- Interior lamp relay coil output.
- Grounded when activated.
- Open circuit when deactivated.
- The RAP module sends a signal to the GEM to turn the illuminated entry on or off.
- Illuminated entry will be canceled if:
- 25 seconds have elapsed since the illuminated entry feature was activated and the courtesy lamp feature is not activated.
- If the GEM receives a request from the RAP and the courtesy lamp feature is not activated.
- If the ignition is in the RUN or START position and the courtesy lamp feature is not activated.

Illuminated entry inputs are:
- Ignition switch in the key-in, ACCY and RUN positions.
- RAP module illuminated entry request.

Power Window Subsystem
- The GEM/CTM provides temporary power to the power windows for ten minutes after the ignition is turned from RUN to OFF.
- If either front door is opened during this period, the power window relay will be de-energized.
- The GEM controls the one-touch down window feature.