Headlamp: Description and Operation

Exterior Lights

How the Headlights Circuit Works

Warning: A transient high tension (25,000 V) occurs at the bulb sockets of the high intensity discharge (HID) lamps when the combination light switch is turned ON. This can cause serious electrical shock or electrocution if you do not observe the cautions below.

Caution:
- Never turn on the combination light switch before fitting the HID bulbs to their bulb sockets and completing the reassembly of the headlight assembly.
- To prevent electrocution, do not service the headlight assembly in wet conditions, such as rain or snow, near a sprinkler system, or when your hands are wet.
- Do not touch the surfaces of the HID bulbs with your bare hands, and do not stain them with any oils or fats.
- Do not disassemble the inverter unit and the igniter unit.
- Do not turn on the HID bulb using a power source other than the battery mounted on the vehicle.

The headlights circuit is controlled by the MICU. The high beam and low beam headlight relays are located within the relay control module. Refer to the multiplex Diagram Set more multiplex information.

Power Supply
Battery voltage is supplied at all times through fuse 7 (in the under-dash fuse/relay box) to the MICU and combination switch control unit. With the ignition switch in ON (II) or START (III), battery voltage is supplied through fuse 21 (in the under-dash fuse/relay box) to the MICU and combination switch control unit.

System Description

High and Low Beams
The high and low beam headlight relays are located within the relay control module. The relays receive battery voltage at all times. The grounding and operation of the relays are controlled by the multiplex system.

The combination switch control unit receives information signals about operating conditions from the headlight switch and from the dimmer switch.

When the headlight switch is turned on and the dimmer switch is set to HIGH or LOW, the information from both switches is processed by the combination switch control unit and transmitted from control unit to control unit across the multiplex communication lines. The relay control module will then ground the appropriate high or low beam relay to operate the necessary headlights.

Flash-to-Pass
The combination switch control unit receives information signals about operating conditions from the headlight switch and from the dimmer switch.

When the dimmer switch is pulled to PASSING, the information from the dimmer switch is processed by the combination switch control unit and transmitted from control unit to control unit across the multiplex communication lines. The relay control module will then ground the high beam relay to operate the passing lights.

Automatic Lighting
The automatic lighting control unit receives battery voltage through fuses 21 and 30 (in the under-dash fuse/relay box) with the ignition switch in ON (II) or START (III). When the headlight switch is in the AUTO position, the combination switch control unit and automatic lighting control unit receive an automatic lighting signal. When the automatic lighting sensor detects low ambient light, the automatic lighting control unit transmits a lights-on signal to the combination switch control unit and relay control module. The relay control module will then ground the appropriate high beam headlight relays to operate the necessary headlights.