Intrusion Sensor - Operation

OPERATION

Each intrusion sensor (also known as interior protection sensors) includes a microprocessor that contains the motion sensor logic circuits. In addition, the front sensor includes the integral inclination sensor for tow-away protection and controls all of the interior motion detection and tow-away protection features. The front sensor interfaces directly with the Roof Control Module (RCM) (also known as the Overhead Control Panel/OCP control unit or DBE), which uses On-Board Diagnostics (OBD) and can communicate with other electronic modules in the vehicle as well as with a diagnostic scan tool using the Controller Area Network (CAN) data bus.

The center and rear intrusion sensors as well as the Motion Sensor OFF and Inclination Sensor OFF switches are powered by and provide direct inputs to the front sensor. The front sensor microprocessor continuously monitors inputs from its on-board motion sensor and inclination sensor circuitry as well as inputs from the other sensors and switches, then relays the evaluated signals to the RCM. The RCM then controls the outputs of the Vehicle Theft Alarm (VTA) system as appropriate.

The motion sensor circuitry of each intrusion sensor transmits ultrasonic signals into the vehicle cabin through a transmit transducer, then listens to the returning signals through a receive transducer as they bounce off of objects in the vehicle interior. If an object is moving in the interior, a detection circuit in the sensor recognizes this movement through the modulation of the returning ultrasonic signals that occurs due to the Doppler effect. The motion detect function of the intrusion sensors can be disabled by turning the ignition switch to the 1 (UNLOCK or ACCESSORY) position and depressing the Motion Sensor OFF switch button on the RCM.

If movement is detected while the VTA is armed, the front sensor sends an electronic signal to the RCM, and the RCM sends electronic messages over the CAN data bus to the Body Control Module (BCM) (also known as the Signal Acquisition and Actuation Module/SAM) to control the exterior lights and horn, and to the optional battery-powered alarm siren module over a dedicated serial bus line to sound the siren.

The inclination sensor integral to the front intrusion sensor contains two electrodes immersed in an electrically conductive fluid. As the attitude of the vehicle changes, so does the immersion levels of the two sensor electrodes and the conductivity value between them. The sensor stores a conductivity value when the alarm is set, then signals the RCM to sound the alarm features when it recognizes a change in the vehicle inclination. The inclination sensor function can be disabled by turning the ignition switch to the 1 (UNLOCK or ACCESSORY) position and depressing the Inclination Sensor OFF switch button on the RCM.

The hard wired circuits of the intrusion and inclination sensors 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 or inclination sensors 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 or inclination sensors or the electronic controls and communication related to their operation requires the use of a diagnostic scan tool. Refer to the appropriate diagnostic information.