Automatic Headlamp Levelling

AUTOMATIC HEADLAMP LEVELLING

DESCRIPTION

General
Automatic headlamp levelling is only fitted to vehicles with bi-xenon headlamps. The system adjusts the vertical positioning of the headlamps to provide optimum headlamp beam position for maximum driving visibility and preventing glare to oncoming drivers.


WARNING: The bi-xenon headlamp system generates up to 28000 volts and contact with this voltage could lead to fatality. Ensure the headlamps are switched off before working on the system.


The system is controlled by the headlamp levelling ECU, which is located at the base of the LH 'A' post. The ECU receives information from the front and rear height sensors and the ABS ECU to maintain the headlamps in the optimum vertical position.

OPERATION

Power Distribution
Feed from the positive battery terminal (C0192) is supplied to fusible link 4 and fuse 53 of the passenger compartment fuse box (C0632) on an R wire. Fusible link 4 (C0590) provides a constant battery feed to the Light Check Module (LCM) (C2039) on an R wire.

Fuse 53 (C0583) provides a constant battery feed to the ignition switch (C0028 on V8 vehicles) on an R wire. When the ignition switch is turned to the 'auxiliary' position, current flows across the switch (C0028 on V8 vehicles) to fuse 9 of the passenger compartment fuse box (C0585) on a PB wire. Fuse 9 (C0587) provides an auxiliary ignition feed to the LCM (C2040) on a PY wire.

Light Check Module
When the engine is running, the Light Check Module (LCM) (C2040) provides a feed to the headlamp levelling ECU (C1543) on a YR wire to initiate the automatic headlamp levelling function.

The LCM (C2040) also monitors the condition of the brake pedal switch (C0075) by providing a feed on a UR wire. This feed allows the headlamp levelling ECU to register when the vehicle is about to decelerate and adjust the vertical position of the headlamps accordingly .

ABS ECU
The ABS ECU (C0506) provides a vehicle speed signal to the headlamp levelling ECU (C1543) on a YW wire. This allows the headlamp levelling ECU to monitor the acceleration of the vehicle and adjust the vertical position of the headlamps accordingly.

RH Front Height Sensor
The headlamp levelling ECU (C1543) provides a 5V reference feed to the RH front height sensor (Cl697) on a WB wire, and provides an earth path on a WN wire. The height sensor (C1697) returns a signal feed back to the headlamp levelling ECU (C1543) on a WS wire. By measuring this signal feed the headlamp ECU can determine the height of the front of the vehicle, compare this to the signal supplied by the RH rear height sensor and adjust the vertical position of the headlamps accordingly.

RH Rear Height Sensor
The headlamp levelling ECU (C1543) provides a 5V reference feed to the RH rear height sensor (C1698) on an SB wire, and provides an earth path on an SN wire. The height sensor (C1698) returns a signal feed back to the headlamp levelling ECU (C1543) on an SW wire. By measuring this signal feed the headlamp ECU can determine the height of the rear of the vehicle, compare this to the signal supplied by the RH front height sensor and adjust the vertical position of the headlamps accordingly.