Grand Cherokee 2WD V8-5.7L VIN 2 (2005)
Ambient Light Sensor: Description and Operation
DESCRIPTION
The Rain Sensor Module (RSM) (4) is the primary component of the automatic wiper system. In vehicles equipped with the automatic wiper system and
the automatic headlamp system the RSM also performs the ambient light sensor function; and therefore is sometimes referred to as the Rain/Light Sensor
Module (RLSM). The RSM is located on the inside of the windshield just below the inside rear view mirror mounting button. The RSM is concealed
from view within the vehicle interior by a cavity in the top of the housing for the SmartBeam camera on the rear view mirror bracket but is visible
through the windshield glass from the exterior of the vehicle. See: Headlamp
The molded black plastic sensor housing has an integral connector receptacle (5) at the top containing four terminal pins. These terminal pins connect the
rain sensor to the vehicle electrical system through a dedicated take out and connector of the overhead wire harness that extends from above the
headliner. Openings on the windshield side of the housing are fitted with eight convex clear plastic lenses. A sliding cam lock retainer (3) on each side of
the sensor housing latches the sensor to four pins (2) on the mounting bracket (1) which is permanently bonded to the inside of the windshield glass with
an adhesive pad.
Concealed and protected within the sensor housing is the electronic circuitry of the module which includes four InfraRed (IR) diodes four photocells and
a microprocessor. The sensor communicates with other electronic modules in the vehicle over the Controller Area Network (CAN) data bus. The rain
sensor sofiware is Flash compatible which means it can be reprogrammed using Flash reprogramming procedures.
The rain sensor sofiware is Flash compatible which means it can be reprogrammed using Flash reprogramming procedures. The hardware of the sensor
cannot be adjusted or repaired. If ineffective or damaged the entire module must be replaced. The RSM mounting bracket is serviced only as a unit with
the windshield glass.
OPERATION
The microprocessor-based Rain Sensor Module (RSM) or Rain/Light Sensor Module (RLSM) senses moisture in the wipe pattern on the outside of the
windshield glass and sends wipe commands to the Front Control Module (FCM). Four InfraRed (IR) diodes within the sensor generate infrared light
beams that are aimed by four of the convex optical lenses near the base of the sensor through the windshield glass. Four additional convex optical lenses
near the top of the sensor are focused on the infrared light beams on the outside of the windshield glass and allow the four photocells within the sensor to
sense changes in the intensity of these infrared light beams. When sufficient moisture accumulates within the wipe pattern on the windshield glass the
sensor detects a change in the monitored infrared light beam intensity.
The internal programming of the sensor then sends the appropriate electronic wipe command messages to the FCM over the Controller Area Network