Description And Operation
DESCRIPTION
Vehicles equipped with the optional automatic headlamp leveling system are also equipped with an Automatic Headlamp Leveling Module (AHLM) (1). The AHLM is located on a bracket behind the center of the upper instrument panel substrate.
This module works in conjunction with the front and rear axle (leveling) sensors, the headlamp leveling motors, and electronic message inputs received over the Controller Area Network-Chassis (CAN-Chassis) data bus from other electronic modules in the vehicle. The module provides automatic headlamp beam aim adjustment to compensate for changes in vehicle height caused by changes in vehicle loading, acceleration, deceleration, and yaw rate.
Concealed within the module housing is the circuitry of the module itself, which includes a microcontroller. The module is connected to the vehicle electrical system through an integral connector receptacle by a take out and connector of the headlamp and dash wire harness.
The AHLM cannot be adjusted or repaired and, if ineffective or damaged, the module must be replaced. The AHLM is Flash programmable.
OPERATION
The AHLM contains the logic circuits and controls all of the features of the headlamp leveling system. The AHLM uses On-Board Diagnostics (OBD) and communicates with other electronic modules and related components in the vehicle as well as with a diagnostic scan tool using the CAN data bus. The AHLM is also a Local Interface Network (LIN) master node and uses this method of communication to communicate with the two stepper motors within each right and left front lamp unit.
The AHLM continuously monitors electronic message inputs from the Body Control Module (BCM). The AHLM also energizes or de-energizes the front and rear axle sensors as appropriate to monitor the vehicle height. When the axle sensors are energized, the AHLM monitors and evaluates the Pulse Width Modulated (PWM) return signals from those sensors.
The AHLM uses these inputs to determine vehicle speed, accelerator pedal position, vehicle yaw rate and Antilock Brake system (ABS) status. It then uses internal programming algorithms to compute the proper electronic message control outputs to provide over the LIN bus to the LIN slave headlamp leveling stepper motor to adjust the headlamp beams horizontally as required. The AHLM also continuously monitors return inputs from the leveling motor to confirm stepper motor responsiveness as well as the proper positioning of the headlamp beams.
The AHLM receives battery voltage on a fused ignition switch output (RUN) circuit, and is grounded at all times through a hard wired remote ground point. These connections allow the AHLM to operate only when the ignition switch is in the ON position. The AHLM also monitors all of the AHLM circuits and components, then sets active and stored Diagnostic Trouble Codes (DTC) for any monitored system faults it detects.