Motion Detector - Operation

OPERATION

The interior lighting motion detector includes a microprocessor that contains the motion detector logic circuits, InfraRed (IR) Light Emitting Diode (LED) units that direct invisible IR light beams into the load compartment of the vehicle, and photodiode receivers that monitor the intensity of the reflected IR light. When there is no movement in the vehicle, some of the IR light is reflected back to the detector at a fixed intensity. When objects are moving within the vehicle, the intensity of the reflected light modulates. This causes changes in the signal output of the motion detector.

The motion detector has a path to ground at all times through a takeout of the vehicle wire harness secured to the body sheet metal. The supply of voltage to the detector is controlled by the BCM. The BCM microprocessor continually monitors a return signal from the motion detector. When the BCM detects a change in the motion detector signal output while the vehicle is stationary, the parking brake is applied or the gear selector lever is in the PARK position, the service brakes are not applied and the vehicle has not been locked from the exterior using a key, it provides an output to the load compartment lighting or light switches. The load compartment lighting switch must be in the AUTOMATIC position for the motion detector feature to operate.

Once movement is detected, the BCM keeps the load compartment lighting circuits energized for about 2 minutes. Each time movement is detected, the 2 minute duration refreshes. The BCM switches the motion detector OFF automatically if no motion has been detected for several hours to prevent the battery from becoming discharged.

The hard wired circuits of the motion detector 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 motion detector or the electronic controls or communication between modules and other devices that provide some features of the automatic interior lighting. The most reliable, efficient, and accurate means to diagnose the motion detector or the electronic controls and communication related to automatic interior lighting operation requires the use of a diagnostic scan tool. Refer to the appropriate diagnostic information.