"Panel" Fuse keeps blowing when 08 LX570 switches to "night-mode".

[JKTrevecca]

Hello all. New member here from middle Tennessee. Thanks in advance if you're reading this! My wife drives our 2008 LX570. I noticed a month or two ago that the vehicle wasn't switching to "night" mode. The NAV screen map was super bright at night and the back-lights on the dash buttons weren't illuminating at night. I found that the "panel" fuse, a 10A fuse, was blown, swapped it, and everything worked perfectly again.... for about 5 seconds. Then the fuse blew again. I bought a 10A circuit breaker that I installed in place of the fuse so I could try to isolate what might be causing it. The circuit breaker keeps tripping at night, randomly. Some times the car will stay in "night mode" for 2 seconds before the breaker trips. Sometimes it will last up to 45 seconds before it trips. This only happens at night when the light sensor on the dash is telling the vehicle to go into "night" mode.

I've removed and taken apart the dimmer switch, visually inspected it and "cleaned" the inside parts of it, re-installed it, with no change in outcomes.

Here is a pic of the fuse box with the circuit breaker installed in place of the fuse.

This vehicle has zero modifications done to it. This started randomly. Vehicle has 120K miles on it.

Any idea's? Suggestions? Anyone else experience this? Thank you!

 

[Sandroad]

Welcome!

Any water get inside recently? Windshield been replaced? Sunroof drains clear? Any mice get to wiring anywhere? Any electrical modes?

There‘s a short somewhere……hmmmmm.

 

[JKTrevecca]

Welcome!

Any water get inside recently? Windshield been replaced? Sunroof drains clear? Any mice get to wiring anywhere? Any electrical modes?

There‘s a short somewhere……hmmmmm.

Thank you for engaging with me!

No water inside at all. Vehicle sits in garage 95% of it's life. Windshield replaced 7 years ago perhaps. Not sure about sunroof drains but since no water is entering the cabin, *assume* they are intact and clear.

I agree there is a short or excessive amperage draw somewhere. Hoping it is/was a common issue on this circuit that others might have experience with.

Do you know where I could find a wiring diagram for this circuit so I can begin to diagnose? Thank you!

 

[Sandroad]

I asked about the windshield because replacements are notorious for eventually leaking (sometimes just a bit) and letting water into connectors. I don’t have a wiring diagram, but someone else reading this may jump in. Smart move on the 10A CB, by the way. I don’t think this issue has been reported before. If it was mine, given the symptoms, I’d start looking at connectors for corrosion. I’d also get a hose on the windshield for a while, then look carefully everywhere under the dash for a drip

 

[bronc076]

When the fuse is blown aside from the screen not transitioning to dim mode and the backlight buttons failing to illuminate what else does not work? What about the instrument panel? I‘m not sure how this system works but let’s think through this. On my 2015 LC if I turn the headlights on in my LC during the day Im pretty sure all the dash lights illuminate but the screen does not go into night mode unless it gets dark. So if you have your car outside in the daylight and turn the headlights on does the fuse blow / breaker trip, or does it require the vehicle to think it’s dark? If so what else turns on in night mode, or should I say what else happens in night mode and how? Could be as simple as a bad relay. Sounds like the car lives a pretty easy life compared to some on here.

 

[bronc076]

From your pic it looks like fuse4?

 

[lx200inAR]

Maybe get a list of all the switches from above, and try to inspect each one while circuit breaker is closed to see if one is brighter or not functioning while the rest are. This sounds like a nightmare to tshoot. Wires for that circuit must run all around the vehicle. Maybe inspecting the dimmer switch there may be some “trunks” you can narrow the short down to.

 

[Sandroad]

Are all those things off when circuit 4 is out?

 

[lx200inAR]

I suspect that circuit is just for the lights in all the switches for those things.

 

[bronc076]

I suspect that circuit is just for the lights in all the switches for those things.

I agree! JK, do all the switches still function and just not illuminate or do they stop working? For instance can you still adjust your mirrors? I’d look for obvious things like has someone spilled a beverage on the center area lately, or check if something got jammed into the glovebox light/switch. Wait, you have a glovebox light? My LC doesn’t. Dang Lexus. . Then I’d start unplugging things and see when the fuse quits popping. Thats after I verified what else changes in night mode. I suspect there is something else going on and all that switch illumination is fine. But it could be a bad switch module. I’d like to see the wiring diagram. I’m sure the photocell sensor sends a signal to a computer which then changes things. I’d look up the diagram but I am away from my computer that has the diagrams, and I’m not sure what module the photocell that senses day/night signals.

I’m sure this is annoying but it’s not impossible to figure out. I might go to the seat switches or steering switches first as they move. It seems more likely the source of a problem than a panel switch on the dash. Have you carried anything in the back seat that could have damaged the heater controls back there? Maybe the shifter illumination has been damaged. I’d unplug all that stuff one at a time.

Hope this helps.

 

[bronc076]

Resistor for Daytime running lights.

This is interesting. DRL are on when lights are off or in auto during day mode. I’m not sure what this resistor does but my guess is since DRLs are just dim high beams it drops the voltage so they are not as bright. Can you expand on your suggestion as I know little about this resistor?

 

[Hoosier Daddy]

This is interesting. DRL are on when lights are off or in auto during day mode. I’m not sure what this resistor does but my guess is since DRLs are just dim high beams it drops the voltage so they are not as bright. Can you expand on your suggestion as I know little about this resistor?

Ouch, it turns out I somehow replied to the wrong thread. Doh! Please disregard my DRL comment.