Commander 4WD V8-4.7L VIN N (2006)
Alarm Horn: Description and Operation
SIREN
DESCRIPTION
An alarm siren module (1) 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. This unit is
designed to provide the audible alert requirements for the premium VTA.
The alarm siren module consists of microprocessor based electronic control circuitry, the siren, and a nickel metal hydride backup battery. All of the
alarm module components are protected and sealed within a molded plastic housing. An integral connector receptacle (2) extends rearward from the top
of the housing and connects the unit to the vehicle electrical system through a dedicated take out and connector of the headlamp and dash wire harness.
The housing also has a threaded insert within the mounting hole (3) on the back through which a screw secures it to a stamped metal mounting bracket.
The siren and bracket unit are located in a hollow behind the right end of the front frame crossmember outboard of the right front frame rail. A single
screw secures the mounting bracket to the right end of the front crossmember.
The alarm siren module cannot be repaired or adjusted and, if ineffective or damaged, it must be replaced.
OPERATION
The microprocessor within the alarm siren module provides the siren unit features and functions based upon internal programming and electronic arm
and disarm messages received from the intrusion module over a dedicated serial bus communication circuit. The siren module receives battery voltage on
a fused B(+) circuit through a fuse in the Power Distribution Center (PDC), and receives a path to ground through a ground circuit in the headlamp and
dash wire harness. These connections allow the siren to remain operational, regardless of the ignition switch position.
When the premium version of the Vehicle Theft Alarm (VTA) is armed, the siren module continuously monitors electronic message inputs from the
intrusion module to sound its internal siren. While armed, the siren also enters its auto-detect mode. While in the auto-detect mode, if the siren module
detects that its power supply or communication circuits are being tampered with or have been sabotaged, it will sound an audible alarm and continue to
operate through an on-board backup battery. If the siren module is in its disarmed mode when its power supply or communication circuits are
interrupted, the siren will not sound.
The siren module will also notify the intrusion module when the backup battery requires charging, and the intrusion module will send electronic
messages that will allow the backup battery to be recharged through the battery voltage and ground circuits to the siren module only while the ignition
switch is in the ON position and the engine is running. This prevents the potential discharge of the main battery while the vehicle is not being operated.
The siren will self-detect problems with its internal and external power supply and communication circuits, then send electronic messages indicating the
problem to the intrusion module upon receiving an arm or disarm request. The intrusion module will store a Diagnostic Trouble Code (DTC) for any
detected alarm siren module fault. The DTC can then be retrieved with a diagnostic scan tool through the 16-way Data Link Connector (DLC) located
under the driver side lower edge of the instrument panel over the Controller Area Network (CAN) data bus.
The hard wired inputs and outputs for the siren may be diagnosed and tested using conventional diagnostic tools and procedures. However, conventional
diagnostic methods will not prove conclusive in the diagnosis of the internal circuitry or the backup battery of the siren module, the intrusion module, the
serial bus communication line, or the electronic message inputs to and outputs from the alarm siren module. The most reliable, efficient, and accurate
means to diagnose the siren, the intrusion module, the serial bus communication line, and the electronic message inputs to and outputs from the siren
requires the use of a diagnostic scan tool.
