Jeep 1997 Grand Cherokee Service Manual page 779

ZG
8W-39 VEHICLE THEFT SECURITY SYSTEM
DESCRIPTION AND OPERATION
INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . 7
DESCRIPTION AND OPERATION
INTRODUCTION
The Body Control Module (BCM) operates the Vehicle
Theft Security System (VTSS). The BCM monitors the
vehicle doors, hood, liftglass in the liftgate, liftgate, and
ignition for unauthorized operation.
When the BCM detects unauthorized operation, it
operates the horn repeatedly for three minutes and
flashes the headlamps and tail lamps for 15 minutes.
Also, the engine will not operate until the VTSS is
disarmed.
The vehicle operator can activate the alarm by pushing
the panic button on the Remote Keyless Entry (RKE)
transmitter. When the operator pushes the panic button,
the radio frequency receiver in the Passenger Door Mod-
ule (PDM) receives the PANIC signal and broadcasts a
message on the CCD bus. When the BCM sees the
PANIC message on the CCD bus, it operates the horn
repeatedly, turns on the interior lights, and flashes the
headlamps and tail lamps. The BCM activates the panic
alarm for three minutes unless the operator starts the
vehicle and drives at a speed above 15 MPH or pushes
the panic button on the RKE transmitter a second time.
When the ignition switch is in the START or RUN
position, it connects circuit A1 from fuse 8 in the
PDC to circuit A21. Circuit A21 powers circuit F99
through PDC fuse 18. Circuit F99 feeds the BCM.
In the ACCESSORY or RUN position, the ignition
switch connects circuit A1 to circuit A31. Circuit A31
powers circuit V23 through fuse 3 in the junction
block. Circuit V23 feeds the BCM.
VEHICLE THEFT SECURITY SYSTEM OPERATION
Each door, the liftgate, hood, and the liftglass in the lift-
gate have an ajar switch that connects to the Body Control
Module (BCM). The ajar switches are normally open when
the doors, liftgate, liftglass and hood are closed. When one
of them open, its ajar switch closes and connects the BCM
to ground. In response, if the Vehicle Theft Security Sys-
tem is armed, the BCM starts the alarm. Refer to the
Introduction in this section for alarm information.
The BCM receives the ajar switch signals on the
following circuits.
• Circuit G75 provides the left front door ajar
switch signal
8W - 39 VEHICLE THEFT SECURITY SYSTEM
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INDEX
VEHICLE THEFT SECURITY SYSTEM
OPERATION . . . . . . . . . . . . . . . . . . . . . . . . . . 7
• Circuit G74 provides the right front door ajar
switch signal
• Circuit G77 provides the left rear door ajar
switch signal
• Circuit G76 provides the right rear door ajar
switch signal
• Circuit G78 provides the liftgate ajar and lift-
glass ajar signals
SYSTEM ARMING
The system alarm sets after the operator uses the
power door locks or Remote Keyless Entry (RKE)
transmitter to lock the doors and liftgate. After all
doors and the liftgate are locked and closed, the BCM
illuminates a red Light Emitting Diode (LED) (VTSS
indicator light) on circuit G69. The red LED is
located on the top of the instrument panel. The LED
flashes rapidly signalling the system is arming. It
flashes at slower rate after approximately 15 sec-
onds, indicating the BCM has set the VTSS.
SYSTEM DISARMING
The operator can disarm the system by unlocking a
front door or the liftgate with the key or the RKE
transmitter. The BCM monitors the lock cylinder
switch in each front door and the liftgate lock cylin-
der switches on circuit G71.
HORNS
When the BCM activates the horns, it energizes
the horn relay by providing a ground path for the
relay coil on circuit X4. Circuit F31 from fuse 6 in
the Power Distribution Center (PDC) powers the coil
and contact sides of the relay.
When the horn relay energize, its contact close and
connect circuit F31 to circuit X2. Circuit X2 feeds the
horns. Circuit Z1 provides ground for the horns.
PARKING LAMPS
The BCM operates the park lamps when it senses
unauthorized entry to the vehicle while the Vehicle
Theft Security System is armed. When it senses
unauthorized entry, the BCM energizes the park
lamp relay by providing ground for the relay coil on
circuit L79. Circuit 366 powers the relay coil and
contacts. When the relay energizes, it connects cir-
cuit 366 to circuit L90. Circuit L90 powers the park
lamps, side marker lamps and tail lamps.
8W - 39 - 7
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