Grand Cherokee 4WD Laredo V8-4.7L (2002)
The microprocessor in the Intrusion Transceiver Module (ITM) contains the motion sensor logic circuits and controls all of the features of the
premium version of the Vehicle Theft Alarm (VTA). The ITM uses On-Board Diagnostics (OBD) and can communicate with other modules in the
vehicle as well as with the DRB III scan tool using the Programmable Communications Interface (PCI) data bus network. This method of
communication is used by the ITM to communicate with the Body Control Module (BCM) and for diagnosis and testing. The ITM also
communicates with the alarm siren over a dedicated serial bus circuit.
The ITM microprocessor continuously monitors inputs from its on-board motion sensor as well as inputs from the BCM and the alarm siren
module. The ITM motion sensor transmits ultrasonic signals into the vehicle cabin through a transmit transducer, then listens to the returning
signals as the bounce OFF of objects in the vehicle interior. If an object is moving in the interior, a detection circuit in the ITM senses this
movement through the modulation of the returning ultrasonic signals that occurs due to the Doppler effect. The motion detect function of the ITM
can be disabled by depressing the "Lock" button on the Remote Keyless Entry (RKE) transmitter three times within fifteen seconds, while the
security indicator is still flashing rapidly or by cycling the key in the driver door cylinder from the center to the lock position. The ITM will signal
the alarm siren module to provide a single siren "chirp" as an audible confirmation that the motion sensor function has been disabled.
If movement is detected, the ITM sends an message to the BCM over the PCI data bus to flash the exterior lighting and send a message to the
alarm siren module over a dedicated serial bus line to sound the siren. When the BCM detects a breach in the perimeter protection through a door,
tailgate, flip-up glass, or hood ajar switch input, it sends an message to the ITM and the ITM sends an message to the BCM over the PCI data bus
to flash the exterior lighting and send a message to the alarm siren module over a dedicated serial bus line to sound the siren. The ITM also
monitors inputs from the alarm siren module for siren battery or siren input/output circuit tamper alerts, and siren battery condition alerts, then sets
active and stored Diagnostic Trouble Codes (DTC) for any monitored system faults it detects. An active fault only remains for the current ignition
switch cycle, while a stored fault causes a DTC to be stored in memory by the ITM. If a fault does not reoccur for fifty ignition cycles, the ITM
will automatically erase the stored DTC.
The ITM is connected to the vehicle electrical system through the overhead wire harness. The ITM receives battery voltage on a B(+) circuit
through a fuse in the Junction Block (JB), and is grounded to the chassis at G303. These connections allow the ITM to remain operational,
regardless of the ignition switch position. The hard wired inputs and outputs for the ITM may be diagnosed and tested using conventional
diagnostic tools and procedures. However, conventional diagnostic methods will not prove conclusive in the diagnosis of the ITM, the PCI data
bus network, or the electronic message inputs to and outputs from the ITM. The most reliable, efficient, and accurate means to diagnose the ITM,
the PCI data bus network, and the message inputs to and outputs from the ITM requires the use of a DRB III scan tool. Refer to the appropriate
diagnostic information.
Fig.9 Siren Remove/Install
SIREN
An alarm siren module is part of the premium version of the Vehicle Theft Alarm (VTA) in the Vehicle Theft Security System (VTSS). The
premium version of the VTA is only available in vehicles built for certain markets, where the additional features offered by this system are
required. The alarm siren module is located in the right front frame rail. This unit is designed to provide the audible alert requirements for the
premium VTA.
