I put this question out several months ago, and haven't been able to diagnose the problem.

The Nav screeen intermittently switches to full bright (day mode) at night and the lower dash control lights go dark. The headlights stay on, the speedometer cluster lights stay lit, and the temp and time lights stay on but are in day (bright) mode. I do NOT have the rheostat / dimmer switch clicked too far which I know would override the day/night automatic dimming. I have tried to isolate the problem. I do not believe it is the automatic light control sensor (top middle of dash) which seems to identify night and day correctly - though it could be. It may be a short in the resistor of the rheostat (dimmer) or possibly even the headlight switch / turn signal switch assembly in the steering wheel, or something else. The Nav screen typically turns bright (day mode) after a few to several minutes of night driving ((it happens in the day too, with the dash lights going dark). Occasionally, after going into day bright mode, the Nav screen will then return to night mode and the dash lights turn on again.

Any ideas or suggestions are welcome. Thank you!

 

I had the same problem a few years back. There's one more sensor on rear deck for automatic lights. I changed it and all is well. However I experienced same problem a few days ago, Nav screen started flickering between day and night mode. I put the dimmer switch to day mode and back couple of times and screen stopped changing mode. If anyone resolved this issue completely I'd like to know about it as well.

 

Where is there a light sensor on the rear deck?

 

I think you need to remove the cover. I saw it when my sub was replaced.

 

The sensor is located on the left (drivers side) rear air vent on the rear deck.

 

Yuri.ber, I think your '01 UL has a vent on the deck (package tray) that is not found on the non-UL '01. Is the sensor visible or is it under the rear deck as Lavrishevo is suggesting? Thanks.

 

I suspected the issue could be in the rear ... when I first experienced the problem last winter, it was just after opening and closing the trunk ... the trunk gets used a lot with 3 sons' sports (hockey/baseball gear) hauled to all the practices and games. The wire loom that runs through the rear body through the trunk lid (left side) to the tail lights may be suspect. Thank you gentlemen.

 

 

Yuri.ber, Thank you for your reply and pic. That rear deck sensor (and vent) is not found on the non-UL LS. If you are experiencing the same issue after having replaced that sensor, it must be something else causing it. I also notice that you, like me, have the '01 and are in a northern climate. I posed the question (again) to my local Lexus technician, and so far no new info. Originally, they had me checking fuses, which wasn't the cause.

 

The symptoms, along with intermittent power, also suggest intermittent ground.

 

I put this question out in the general LS forum, and haven't been able to diagnose the problem.

The Nav screeen intermittently switches to full bright (day mode) at night and the lower dash control lights go dark. The headlights stay on, the speedometer cluster lights stay lit, and the temp and time lights stay on but are in day (bright) mode. I do NOT have the rheostat / dimmer switch clicked too far which I know would override the day/night automatic dimming. I have tried to isolate the problem. I do not believe it is the automatic light control sensor (top middle of dash) which seems to identify night and day correctly - though it could be. It may be a short in the resistor of the rheostat (dimmer) or possibly even the headlight switch / turn signal switch assembly in the steering wheel, or something else. The Nav screen typically turns bright (day mode) after a few to several minutes of night driving ((it happens in the day too, with the dash lights going dark). Occasionally, after going into day bright mode, the Nav screen will then return to night mode and the dash lights turn on again.

Any ideas or suggestions are welcome. Thank you!

 

Any change in behavior if the headlight switch is clicked to manual headlight mode or Off stead of Auto mode?

 

Great question ... no change in either "manual" or "auto" light mode on the light switch.

 

Even if the headlight switch is on the "park" lights setting (first click on), the Nav goes into day mode, and the dash lights are out.

 

The symptom occurs shortly after starting and driving the vehicle. After shutting the car off and letting it sit for awhile, re-start and no symptom until a few to several minutes of driving again. Also, it seems that the cooler / colder weather conditions are relevant. I experienced the same symptom last winter, then with the warmer weather over summer, no issues. Now with cold weather again, the symptom has returned.