Operation

OPERATION

The controller board and logic circuitry of the headlamp leveling motor controls motor operation based upon a voltage signal input received from one of two sources. In vehicles with the standard halogen headlamps, the Body Control Module (BCM) (also known as the Signal Acquisition and Actuation Module/SAM) controls leveling motor operation based upon resistor multiplexed inputs received from the headlamp leveling switch on the instrument panel near the headlamp switch. Vehicles equipped withe the optional xenon (also known as bi-xenon or High Intensity Discharge/HID) headlamps are equipped with an automatic headlamp leveling system, which uses an Automatic Headlamp Leveling Module (AHLM) (1) (also known as the Adaptive Lighting, Headlamp Range Adjustment/HRA or LWR module) to automatically control the headlamp leveling motors.

When the motor is energized it will extend or retract the motor pushrod through the integral screw-drive transmission. The ball on the end of the pushrod is snapped into a guide on the back of the reflector within the front lamp unit housing, which will cause the reflector to move as the pushrod is extended or retracted, changing the angle at which the light is projected from the headlamp low and high beam bulbs. The headlamp leveling motors and switch have a path to ground at all times. The headlamp leveling system will only operate when the exterior lighting is turned ON.

The hard wired circuits of the headlamp leveling motors 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 motors or the electronic controls or communication between modules and other devices that provide some features of the manual or automatic headlamp leveling systems. The most reliable, efficient, and accurate means to diagnose the headlamp leveling motors or the electronic controls and communication related to manual or automatic headlamp leveling system operation requires the use of a diagnostic scan tool. Refer to the appropriate diagnostic information.