DESCRIPTION & OPERATION
Note. Some models use a multiplex control system. Check multiplex control system. See appropriate MULTIPLEX CONTROL SYSTEMS article.
When headlight switch is in AUTO position, system automatically turns on the low-beam headlights (and taillights) if it is dark enough outside. When it is not dark enough, the system automatically turns headlights off. If driver leaves the headlight switch in AUTO position and turns ignition off, headlights will go out when driver's door is opened. If headlights come on too early or too late, system sensitivity can be adjusted. See LIGHT SENSOR under ADJUSTMENTS.
When intensity of light decreases sufficiently, light sensor internally grounds coil circuit of headlight relay (through headlight switch), causing headlight relay contacts to close, allowing power to headlights. When intensity of light increases sufficiently, light sensor interrupts the internal connection.
When driver's door is open, light sensor detects closed contacts in door courtesy switch. Light sensor uses this signal to turn off headlights, if headlight switch is in AUTO position when ignition is turned off.
On GS300 and GS400 models, automatic headlight is controlled by light control ECU. On LS400 models, automatic headlight is controlled by driver's door ECU and body ECU.
SYSTEM OPERATIONAL TEST
- Turn ignition on. Turn headlight switch to AUTO position. Gradually cover light sensor. Headlights and instrument panel lights should come on. Gradually uncover light sensor. Lights should turn off.
- Gradually cover light sensor. Wait for lights to come on. Lights should turn off under any of the following conditions: Headlight switch is turned to OFF position. Light sensor is exposed. Ignition is turned off and driver's door is opened.
- Turn ignition off. Open driver's door (leave it open). Ensure light sensor is uncovered. Turn ignition on. Lights should turn off.