Ultrasonic Sensor: Description and Operation

INTRUSION SENSOR

DESCRIPTION

TRANSMITTER




An intrusion sensor transmitter (2) 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 work in conjunction with the intrusion sensor receiver to provide interior motion detection inputs to the intrusion module, which serves as the interface between the Forward Control Module (FCM), the Electromechanical Instrument Cluster (EMIC) and the alarm siren.

The transmitter is located in the passenger compartment, where it is concealed behind the headliner. A molded plastic mounting bracket with two locating pins engages the holes in two locating tabs (4) integral to the transmitter housing and the housing is secured in place by two latch features integral to the bracket. Only a small dedicated molded plastic transducer trim bezel that is secured by a snap fit to the tubular ultrasonic transducer housing, which extends horizontally outward from the base of the transmitter housing is visible on the vertical surface in the left rear corner of the headliner. The trim bezel has a small round opening that faces the front of the vehicle through which the transducer is aimed.

Concealed within the molded plastic transmitter housing is the circuitry of the transmitter which includes an ultrasonic transmit transducer (1). The transmitter is connected through an integral connector receptacle (3) to the vehicle electrical system by a take out and connector of the overhead wire harness that is integral to the headliner.

The intrusion sensor transmitter cannot be adjusted or repaired and, if ineffective or damaged, it must be replaced. The transmitter mounting bracket is serviced as a unit with the headliner. The transducer trim bezel is available for separate service replacement.

RECEIVER




An intrusion sensor receiver (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 work in conjunction with the intrusion sensor transmitter to provide interior motion detection inputs to the intrusion module, which serves as the interface between the Forward Control Module (FCM), the Electromechanical Instrument Cluster (EMIC) and the alarm siren.

The receiver is located in the passenger compartment, where it is concealed above the headliner. A molded plastic mounting bracket with three integral latch features is secured to the left rear corner of the overhead console housing and engages three latch tabs integral to the receiver housing. The ultrasonic receiver transducer (2) is aimed through a small dedicated round opening in the left side of the overhead console and is the only evidence of the receiver that is visible from the passenger compartment.

Concealed within the molded plastic receiver housing is the circuitry of the receiver which includes the receive transducer. The receiver is connected through an integral connector receptacle (3) to the vehicle electrical system by a take out and connector of the overhead wire harness that is integral to the headliner.

The intrusion sensor receiver cannot be adjusted or repaired and, if ineffective or damaged, it must be replaced. The receiver mounting bracket is serviced as a unit with the overhead console.

OPERATION

TRANSMITTER
The intrusion sensor transmitter operates only when it is energized by the intrusion module. The transmitter generates ultrasonic signals into the vehicle cabin through a transmit transducer. Then the intrusion sensor receiver listens to the returning signals as they bounce off of objects in the vehicle interior and provides input signals to the intrusion module. If an object is moving in the interior, a detection circuit in the intrusion module senses this movement through the modulation of the returning signals that occur due to the Doppler effect. The intrusion module monitors the current draw of the transmitter circuits to determine the condition of the transmitter and, if the draw is too high or too low, it will store a Diagnostic Trouble Code (DTC) for any fault that is detected.

The hard wired circuits for the transmitter may be diagnosed and tested using conventional diagnostic tools and procedures. However, conventional diagnostic methods will not prove conclusive in the diagnosis of the intrusion module, the Controller Area Network (CAN) data bus, or the electronic message inputs to and outputs from the intrusion module. The most reliable, efficient, and accurate means to diagnose the intrusion sensor transmitter, the intrusion module, the CAN data bus and the message inputs to and outputs from the intrusion module requires the use of a diagnostic scan tool.

RECEIVER
The intrusion sensor receiver operates only when it is energized by the intrusion module. The receiver monitors ultrasonic signals generated in the vehicle cabin by the intrusion sensor transmitter through a receive transducer. The receiver listens to the ultrasonic signals as they bounce off of objects in the vehicle interior and provides input signals to the intrusion module. If an object is moving in the interior, a detection circuit in the intrusion module senses this movement through the modulation of the returning signals that occur due to the Doppler effect. The intrusion module monitors the current draw of the receiver circuits to determine the condition of the receiver and, if the draw is too high or too low, it will store a Diagnostic Trouble Code (DTC) for any fault that is detected.

The hard wired circuits for the receiver may be diagnosed and tested using conventional diagnostic tools and procedures. However, conventional diagnostic methods will not prove conclusive in the diagnosis of the intrusion module, the Controller Area Network (CAN) data bus, or the electronic message inputs to and outputs from the intrusion module. The most reliable, efficient, and accurate means to diagnose the intrusion sensor receiver, the intrusion module, the CAN data bus and the message inputs to and outputs from the intrusion module requires the use of a diagnostic scan tool.