Grand Cherokee 4WD V8-5.7L (2008)
Headlamp Alignment Sensor: Description and Operation
Operation
OPERATION
The front and rear axle 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 Levelling Module (AHLM), 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 vehicle frame 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.
