B4000 SE Regular Cab 4WD V6-4.0L OHV (1999)
Generic Electronic Module (GEM): Description and Operation
Multi-Function Control Modules
The remote anti-theft personality (RAP) module controls the keyless entry and computer operated locks systems.
The generic electronic module (GEM) is equipped on vehicles with four-wheel drive or with power windows. The central timing module (CTM) is
equipped on vehicles with two-wheel drive or vehicles without power windows.
NOTE: GEM/CTM diagnostics are compatible with New Generation STAR (NGS) Tester.
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 under its control and reports a concern in the form of a diagnostic trouble code (DTC). A DTC can be
retrieved with NGS Tester through the communication link.
The NGS Tester is a menu-driven tester that allows the user to run specific diagnostic tests. It can isolate faults in the GEM/CTM subsystems through a
symptom-driven diagnostic procedure. Connecting the NGS Tester to the GEM/CTM communication link will not alert the GEM/CTM. If the
GEM/CTM is in sleep mode when the diagnostic connector is plugged in, the GEM/CTM must be activated. If the communication link cannot be
established, the Tester will advise to turn the ignition to ON. The GEM/CTM control system has two modes of operation, the normal operating mode and
the tester dependent diagnostics mode.
NOTE: The GEM/CTM can only detect open circuit/ short to ground 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.
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:
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GEM/CTM continuous self-test (RAM, ROM, EEPROM, ND checking).
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Output driver monitoring (open circuit/short to GND, short to battery).
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Illogical combinations of input signals.
Subsystems
The GEM/CTM controls five modes of operation for the wiper: MIST, INTERVAL, LOW, HIGH and WASH.
These modes are active only when the ignition switch is in the ON or ACC position.
The GEM/CTM responds to the windshield wiper control commands by interpreting inputs from the steering column seven-position delay/wash and
four-position mode select switches.
The GEM/CTM relay drivers control three external relays: wiper high/low speed relay, park lamps relay, and washer pump relay.
The GEM/CTM controls all audible chimes and warning lights. The GEM/CTM performs a prove out on all GEM/ CTM controlled warning light
indicator bulbs (except the seat belt and door ajar) by turning on the bulb for two seconds after the ignition switch is turned to ON from START.
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 the dome lamp, and map lamp for 45 minutes after the ignition switch is
turned off. The battery saver time is reset by receiving an illuminated entry request, activating a door ajar switch, changing the ignition to START, or
moving the key to the ON or ACC position.
The battery saver feature removes extended interior lamp power drains to the battery. The GEM/CTM keeps 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/CTM will enter a sleep mode. During the sleep mode, the GEM/CTM maintains all of its outputs in a deactivated state until a wake-up
command is received. For additional information, refer to INTERIOR LIGHTING DIAGNOSIS.
A wake-up command is sent when:
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A change in door state from open to closed, or closed to open occurs.
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The key is inserted or removed.
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The ignition switch is turned from OFF to ON.
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The ignition switch is turned from OFF to ACC.
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A wake-up request is received from the remote anti-theft personality (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:
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All door ajar switches.
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Illuminated entry request with RAP module.
All interior courtesy lamps are turned off when any of the following occurs:
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All the doors are closed and the illuminated entry feature is not active.
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The ignition switch is turned to ON.
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Vehicle speed is over 8 kph (5 mph).
