Alarm Module: Description and Operation
The microprocessor in the intrusion module contains the motion detection logic circuits and controls all of the features of the premium version of the
Vehicle Theft Alarm (VTA). The module uses On-Board Diagnostics (OBD) and can communicate with other modules in the vehicle as well as with a
diagnostic scan tool using the Controller Area Network (CAN) data bus. This method of communication is used by the module to communicate with the
Front Control Module (FCM) and the ElectroMechanical Instrument Cluster (EMIC) (also known as the Cab Compartment Node/CCN). The module
also communicates with the alarm siren over a dedicated serial bus circuit.
The intrusion module microprocessor continuously monitors inputs from the intrusion sensor transmitter and receiver as well as inputs from the EMIC
and the alarm siren module. The module energizes the intrusion sensor transmitter, which transmits ultrasonic signals into the vehicle cabin through a
transmit transducer, then monitors the current draw of the transmitter to detect problems with the transmitter and transmitter circuits. The module also
energizes the intrusion sensor receiver, which listens to the ultrasonic signals through a receive transducer as they bounce off of objects in the vehicle
interior, then monitors the current draw of the receiver for data signals and to detect problems with the receiver and receiver circuits. If an object is
moving in the interior, a detection circuit in the module senses this movement through the modulation of the returning data signals from the receiver.
If movement is detected, the intrusion module sends an electronic message to the FCM over the CAN data bus to flash the exterior lighting and sends
another message to the alarm siren module over the dedicated serial bus line to sound the siren. When the EMIC or FCM detect a breach in the perimeter
protection through a door, liftgate, flip-up glass, or hood ajar switch input, they send an electronic message to the intrusion module and the module sends
a message to the FCM to flash the exterior lighting and a message to the alarm siren module to sound the siren. The module also monitors message 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 module. If a fault does not recur for 50 ignition cycles, the module will automatically erase the
The intrusion module receives battery voltage on a fused B(+) circuit through a fuse in the Junction Block (JB), and is grounded at all times through a
hard wired remote ground point. These connections allow the module to remain operational, regardless of the ignition switch position.
The hard wired circuits of the intrusion module may be diagnosed using conventional diagnostic tools and procedures. Refer to the appropriate wiring
information. However, conventional diagnostic methods will not prove conclusive in the diagnosis of the intrusion module or the electronic controls or
communication between modules and other devices that provide some features of the VTA. The most reliable, efficient, and accurate means to diagnose
the intrusion module or the electronic controls and communication related to intrusion module operation requires the use of a diagnostic scan tool. Refer
to the appropriate diagnostic information.