Vehicle Theft Alarm: Notes

WARNING: This page is about a different car, the 2017 Jeep Cherokee. However, it is still accessible from the selected car via links, so may be relevant.

The base version of the Vehicle Theft Alarm (VTA) is designed to provide either active or passive perimeter protection of the vehicle by monitoring the vehicle doors, the ignition and the liftgate. In vehicles built for certain markets where it is required equipment, the perimeter protection also includes monitoring of the hood. If the VTA system detects any attempt to compromise a monitored vehicle system or feature, the vehicle horn is pulsed as an audible deterrent and certain exterior lamps are flashed as a visual deterrent.

The Body Control Module (BCM) includes the logic and control circuits for the base versions of the VTA. Each of the ajar switches provides hard wired inputs to the BCM, while the BCM provides control outputs to the vehicle horns and lighting systems. The Radio Frequency Hub Module (RFHM) monitors the status of the ignition switch (IGnition Node Module/IGNM or Keyless Ignition Node/KIN) through a private serial bus and relays this information to the BCM as electronic messages transmitted over the Controller Area Network (CAN) data bus.

The premium version of the VTA includes an Ultrasonic and Antitilt Module (UAM). The UAM provides interior intrusion protection as well as vehicle tow-away and tire theft protection. The UAM includes the logic and control circuits for these features of the VTA and is also a slave node communicating over the Local Interface Network (LIN) data bus. The UAM is armed and disarmed by electronic messages received over the LIN data bus from the BCM, which is a LIN master node. While armed, the UAM uses external ultrasonic transmit and receive transducers to monitor the vehicle interior for movement as well as internal accelerometers to monitor vehicle pitch and roll. When an exception is detected, the UAM relays this information to the BCM over the LIN bus, and the BCM invokes the VTA audible and visual alerts. In vehicles with an ITM, the horn output function of the BCM is replaced by an output of the alarm siren module that is controlled by the BCM over the LIN data bus.

The hard wired circuits between components related to the VTA system may be diagnosed using conventional diagnostic tools and procedures. Refer to the appropriate wiring information. The wiring information includes wiring diagrams, proper wire and connector repair procedures, details of wire harness routing and retention, connector pin out information and location views for the various wire harness connectors, splices and grounds.

However, conventional diagnostic methods will not prove conclusive in the diagnosis of the VTA system or the electronic controls and communication between modules and devices that provide some features of the VTA system. The most reliable, efficient and accurate means to diagnose the VTA system or the electronic controls and communication related to VTA system operation requires the use of a diagnostic scan tool. Refer to the appropriate diagnostic information.