Headlamp Alignment Control Module: Description and Operation

GF82.10-P-0001B Headlamp Range Adjustment (HRA), Function

MODEL 203 up to Model Year 8

Vehicles with xenon headlamps are required by law to possess an electrically controlled headlamp range adjustment system. The headlamp range adjustment system prevents oncoming traffic from being dazzled. It keeps the incline angle of the low beam, irrespective of the vehicle's load, automatically within the legally prescribed limits. The headlamp range adjustment is controlled by the xenon headlamp control unit (E1n1) in the left front lamp unit (E1) and the xenon headlamp control unit (E2n1) in the right front lamp unit (E2). To correct the incline angle the left headlamp range adjustment motor (E1m1) and the right headlamp range adjustment motor (E2m1) are installed. A headlamp range adjustment front axle sensor (A52) and a headlamp range adjustment rear axle sensor (A51) record the vehicle level for the xenon headlamp control unit (E1n1) and the xenon headlamp control unit (E2n1).

The xenon headlamp control unit (E1n1) and xenon headlamp control unit (E2n1) evaluate the sensor signals and actuate, where necessary, the left headlamp range adjustment motor (E1m1) and right headlamp range adjustment motor (E2m1) to correct the incline angle. In addition to the signals from these sensors the ESP and BAS control unit (N47-5) also monitors the vehicle status at any given time with the aid of the wheel rpm signals from the rpm sensors: left front rpm sensor (L6/1), right front rpm sensor (L6/2), left rear rpm sensor (L6/3) and right rear rpm sensor (L6/4). Evaluation of the wheel rpm signal indicates to the ESP and BAS control unit (N47-5), whether the vehicle is traveling at constant speed, accelerating or braking.

At a constant vehicle speed the headlamp range adjustment operates in "static mode" with a low motor adjustment rate.

If the vehicle is accelerating or braking, it activates the "dynamic mode" with a high adjustment rate.