Grand Cherokee 2WD V8-4.7L Flex Fuel (2008)
Headlamp Alignment Actuator: Description and Operation
Headlamp Leveling Module
Description
DESCRIPTION
An Automatic Headlamp Leveling Module (AHLM) (1) is standard equipment with the optional High Intensity Discharge (HID) headlamps. The AHLM
is located on the bottom of the right front lamp unit housing, but serves both the right and left front lamp units. This module works in conjunction with
the front and rear axle sensors and the headlamp leveling motors to provide automatic headlamp beam adjustment to compensate for changes in vehicle
height cased by changes in vehicle loading, acceleration or deceleration.
The molded black plastic AHLM housing has integral mounting flanges (4) that are secured by a stamped aluminum cover plate and four screws to a
receptacle in the bottom of the right front lamp unit housing. Concealed within the housing is the circuitry of the module, which includes a
microprocessor. The module is connected through an integral connector receptacle (2) to the vehicle electrical system by a take out and connector of the
right front lamp unit wire harness.
The AHLM cannot be adjusted or repaired and, if ineffective or damaged, it must be replaced.
Operation
OPERATION
The microprocessor in the Automatic Headlamp Leveling Module (AHLM) 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) (also known as the
Wireless Control Module/WCM or Sentry Key REmote Entry Module/SKREEM) 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.
