Headlamp Leveling Sensor

Headlamp Leveling Sensor

Description

Two axle sensors (1) are used on vehicles manufactured for certain export markets and equipped with the optional High Intensity Discharge (HID) headlamps. One sensor is used to monitor the front suspension and another to monitor the rear suspension of the vehicle. The front and rear sensors are identical, but are secured by bolts to unique fixed brackets that are mounted to a frame member above the left front suspension lower control arm or above the left rear suspension rear axle lower control arm. The sensor has a mechanical lever arm (3) that rotates a sensor input shaft. The opposite end of the lever arm is secured by a ball stud (4) to a unique linkage that is articulated by the changing positions of the left front or left rear suspension members in relationship to the body of the vehicle.






The axle sensor housing has an integral connector receptacle (2) and integral mounting hole. A cavity in the center of the molded plastic axle sensor housing contains the electronic circuitry of the sensor. The sensor housing is sealed to enclose and protect the internal electronic circuitry and components. The sensors are each connected to the vehicle electrical system through a dedicated take out and connector of the vehicle underbody wire harnesses.

The sensor, the unique mounting brackets and the linkage are serviced only as a complete unit. The sensors cannot be repaired or adjusted and, if damaged or ineffective, they must be replaced. The linkage ball stud mounted on the rear axle left lower control arm is available for separate service replacement.

Operation

The front and rear sensors monitor changes in the relative distance between the vehicle body and the front or rear suspension members. Both sensors provide inputs to the Automatic Headlamp Leveling Module (AHLM) (also known as the High Intensity Discharge Transducer/HIDT), which uses these sensor inputs as logic for calculating when and how much to adjust the headlamp beams as part of the automatic headlamp leveling feature.

The body of the sensors are mounted in a fixed position, while the sensor lever arm is attached to a linkage arranged between the sensor and the front or rear suspension members. The sensor circuitry is energized by the AHLM. As the sensor lever arm is moved, it rotates an input shaft. The input shaft rotation is monitored by the sensor circuitry, which causes changes in the Pulse Width Modulated (PWM) output signal of the sensor. The AHLM evaluates the modulated output signals from both sensors to determine what changes are occurring in the front and rear suspension height of the vehicle.

The hard wired circuits for the axle 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 axle sensors or the electronic controls and communication that provide the features of the automatic headlamp leveling system. The most reliable, efficient, and accurate means to diagnose the axle sensors or the electronic controls and communication related to automatic headlamp leveling system operation requires the use of a diagnostic scan tool. Refer to the appropriate diagnostic information.