Headlamp Levelling (Xenon headlamps only)

LIGHTING

DESCRIPTION AND OPERATION 86-2-19

The xenon headlamp unit is a self contained unit located within the headlamp assembly. The unit comprises a 
reflector, an adaptor ring, the lens, a shutter controller and the xenon bulb.

The lens is curved and provides the mounting for the xenon bulb. The bulb locates in two recesses to ensure correct 
alignment in the reflector and is secured with a retention ring. The retention ring locates over the bulb and is turned 
clockwise to lock the bulb in the holder. The bulb has a two pin connector which is also a push and turn to lock fitting.

The adapter ring is attached to the reflector and provides for the attachment of the lens. The lens is attached to the 
adapter ring with an internal spring clip.

The shutter controller is a solenoid which operates, via a lever mechanism, the shutter. The shutter is used to change 
the beam projection from dip beam to main beam and visa versa.

A beam adjustment mechanism is located between the reflector and the adapter ring. This mechanism rotates to blank 
off a portion of the beam spread to enable the vehicle to be driven in opposite hand drive markets without applying 
blanking decals to the headlamp lens. The beam is changed by removing the access cover at the rear of the lamp 
assembly and moving a small lever located near the bulb holder, at the side of the reflector.

Crash Signal Activation
In the event of an accident of a severity to activate and deploy the airbags, the DCU requests various electrical 
operations to assist with the crash situation. The DCU requests via the bus systems to the LCM to activate the hazard 
warning lamps.

Security System Activation
In the event of the security system being triggered, the BCU requests activation of the hazard warning lamps. In some 
markets the low beam and/or high beam headlamps can also be activated.

Headlamp Levelling (Xenon headlamps only)
The automatic headlamp levelling system automatically adjusts the vertical positioning of the headlamps to provide 
the optimum headlamp beam position for maximum driving visibility and preventing glare to oncoming drivers. 

The system is controlled by an automatic headlamp levelling ECU located at the bottom of the LH 'A' post. The ECU 
is connected to and receives information from the Hall effect front and rear height sensors which are also used by the 
air suspension system. The ECU also receives a signal from the ABS ECU for vehicle acceleration. The ECU has 
diagnostic capabilities and can communicate with TestBook/T4 via the K Bus, the instrument pack and the DS2 Bus.

The levelling system is a fast response system which reacts to changes of vehicle angle when driving. The ECU 
receives vehicle speed signals from the ABS ECU and a brake switch signal from the LCM. These two signals are 
used to adjust the headlamp position to compensate for changes in vehicle attitude due to acceleration or braking.

Stepper motors, located as part of the headlamp unit, drive a threaded rod which moves the lower edge of the 
headlamp forward or backwards to adjust the vertical position of the headlamp beam. The stepper motors are 
controlled by the ECU which, using the data from the height sensors, determines the attitude of the vehicle and 
compensates for load differences at the rear of the vehicle or changing driving conditions.