Auto Headlight Question!

[donald]

My 98 GS300 has an issue with the auto headlight feature. When it is on auto only the parking lights come on...no matter how dark it is the headlights will not turn on.

Any thoughts? I know there is a sensor on the dash but not sure if I should replace it??

This forum has been helpful. Thanks.

[TurboGS300]

You can check the sensor easily enough with a DMM and simulating day or night conditions. It maybe just unplugged from someone who previously worked on the car. <_<

[donald]

You can check the sensor easily enough with a DMM and simulating day or night conditions. It maybe just unplugged from someone who previously worked on the car. <_<

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I tried it out in complete darkness in my garage last night. The headlights did not come on...only the parking lights. What is a DMM?

[TurboGS300]

Digital Multimeter <_<

[Matthew_McNally]

you can turn them on manually?

so - we know its not a problem with the bulbs?

[donald]

you can turn them on manually?

so - we know its not a problem with the bulbs?

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Yes I can turn them on manually and they function properly except for the auto feature.

[GuyTelefunken]

Actually, on 1998+ cars the photo sensor does not output a signal that can be checked with a DMM reliably. The signal is a square wave varying from 50Hz (dark) to 1200 Hz (bright). You would need an oscilloscope to check it.

Best bet is the dealer. The Lexus handheld computer can check the operation of this and all other systems on the car in a matter of minutes.

I have a question: Does your gauge illumination (and other dash lights) dim at night, even if you leave the headlights in the off position? They should, they are based on the same sensor.

Test: Park in a dark garage or outside in the dark at night, away from overhead lights. Start the car, headlights in the off position, dash dimmer all the way up. The dash should light, but not be lit at full brightness. Take your handy flashlight and focus it on the sensor at the bottom edge of the windshield. Within a few seconds, the dash lights should switch to full brightness (as they are in daylight.) Turn off the light, wait a bit, should switch to dim.

If the test works, the sensor is working and you have a problem elsewhere. If not, the sensor is a good place to start. Make sure to check all fuses and wiggle all relays before you start though. As always, fuses should be checked with a test lamp.

[donald]

Actually, on 1998+ cars the photo sensor does not output a signal that can be checked with a DMM reliably. The signal is a square wave varying from 50Hz (dark) to 1200 Hz (bright). You would need an oscilloscope to check it.

Best bet is the dealer. The Lexus handheld computer can check the operation of this and all other systems on the car in a matter of minutes.

I have a question: Does your gauge illumination (and other dash lights) dim at night, even if you leave the headlights in the off position? They should, they are based on the same sensor.

Test: Park in a dark garage or outside in the dark at night, away from overhead lights. Start the car, headlights in the off position, dash dimmer all the way up. The dash should light, but not be lit at full brightness. Take your handy flashlight and focus it on the sensor at the bottom edge of the windshield. Within a few seconds, the dash lights should switch to full brightness (as they are in daylight.) Turn off the light, wait a bit, should switch to dim.

If the test works, the sensor is working and you have a problem elsewhere. If not, the sensor is a good place to start. Make sure to check all fuses and wiggle all relays before you start though. As always, fuses should be checked with a test lamp.

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Sounds great....I will try that. I think the lights do dim as you mention above but I will double check. Thanks.