Axle Sensor - 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. In vehicles with High Intensity Discharge (HID) headlamps but without the air suspension system, the sensor circuitry is energized by the Automatic Headlamp Leveling Module (AHLM) (also known as the Headlamp Leveling Module/HLM) and both sensors provide hard wired analog (potentiometer) inputs back to the AHLM. The AHLM 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.

In vehicles with the air suspension system, all four sensors are energized by the Air Suspension Control Module (ASCM) and provide hard wired digital Pulse Width Modulated (PWM) inputs back to the ASCM. The ASCM uses these sensor inputs as logic for calculating when and how much to adjust the suspension as part of the air suspension feature. The ASCM then places the appropriate sensor data on the Controller Area Network (CAN) data bus for retrieval by the AHLM.

The body of each sensor is mounted in a fixed position, while the sensor lever arm is attached to a linkage arranged between the vehicle chassis and the front or rear suspension members. Each sensor is capable of either analog or digital outputs. The output type is determined by the wiring connections to the pins in the sensor connector receptacle. The sensor circuitry is energized by the AHLM or the ASCM. 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 output signal of the sensor. Both the AHLM and the ASCM evaluate the output signals from the 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 and the air suspension 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 or air suspension system operation requires the use of a diagnostic scan tool. Refer to the appropriate diagnostic information.