Headlamp Leveling Module - Operation

OPERATION

The microprocessor within the Automatic Headlamp Leveling Module (AHLM) (also known as the High Intensity Discharge Transducer/HIDT) contains the logic circuits and controls all of the features of the automatic headlamp leveling system. The AHLM uses On-Board Diagnostics (OBD) and can communicate with other modules in the vehicle as well as with a diagnostic scan tool using the Controller Area Network (CAN) data bus. This method of communication is used by the AHLM to communicate with the ElectroMechanical Instrument Cluster (EMIC) (also known as the Cab Compartment Node/CCN), the Wireless Ignition Node (WIN) and with the Controller Antilock Brake (CAB) (also known as the Antilock Brake System/ABS or Electronic Stability Program/ESP controller).

The AHLM microprocessor continuously monitors inputs from the EMIC, the WIN and the CAB. The AHLM then energizes or de-energizes the front and rear axle sensors which monitor the vehicle height, and the headlamp leveling motors which adjust the headlamp reflectors. When the axle sensors are energized, the AHLM monitors and evaluates the Pulse Width Modulated (PWM) signals from the sensors and actuates the headlamp leveling motors on each front lamp unit as appropriate. The AHLM also monitors all of the system circuits, then sets active and stored Diagnostic Trouble Codes (DTC) for any monitored system faults it detects.

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 hard wired circuits of the AHLM 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 AHLM or the electronic controls or communication between modules and other devices that provide some features of the automatic headlamp leveling system. The most reliable, efficient, and accurate means to diagnose the AHLM 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.