Tom57

Putting this question back to the top ... it may be a bad circuit board > resistor or cold solder joint?

Tom57

I'm bumping this question back up since I have new information, possibility isolating and diagnosing the problem. I dialed the rheostat / dimmer control down to the lowest setting / dimmest setting of dash lights "on", and so far I have not experienced the Nav switching to bright day mode at night. Does the mean that the dimmer control (rheostat) is likely the problem, or does the dimmer control interact with another electrical component that regulates the interior dash and Nav lights? The light sensor on the dash under the windshield appears to operate correctly, dimming the dash lights in dark conditions. Thanks for your input.

KING

iTrader: (1)

When the dimmer clicks on clockwise, that means it's on maximum illumination, so the screen will always be on and in full brightness.
Just turn it counterclockwise until it clicks, then the screen won't be so bright.
Plus, you can change how the screen behaves at night from the menu. You can select for it to be dimmer at night.

Hope that answers something.

Tom57

I wish it was such an easy adjustment, KINg911. Post # 1 above states: I do NOT have the rheostat / dimmer switch clicked too far which I know would override the day/night automatic dimming.

Jin3198

Well sorry to bump such an old thread, but I was having this issue on my 02 with the nav randomly staying in day mode and not switching to night mode and having no center console lights. I searched and didn't find anyone being able to solve this issue, so I hope this info will help someone.

Replacement of the rheostat control(dimmer) switch fixed all my problems. I work for toyota so I was able to do some trouble shooting with wiring diagrams after having this issue get worse and worse over the last 1/2 year. I had my parts dept order me a new switch and found out that there was an updated part.

Before I actually ordered the part, I did some minor troubleshooting by testing the old switch and seeing if it was changing signals from "locked" in day mode (all the way clockwise after the click) and turning it counter clock wise to get it out of "day mode". What I found was the signal not always sending and or intermittently jumping back and forth with the signal.

The new update part # is 84119-50230 and there is a minor difference in the new part as it has 2 leds(one red and one green), where as the old one is just a single red led for the security light.

Good luck and I hope this will be useful for someone with the same issues.

Tom57

Very interesting that yours was the rheostat Jin3198, which is what I thought was my issue, but it wasn't. After much diagnosis, I DIY replaced the driver's side J/B with a recycled one and haven't had any problem with Day Mode at night. As I'm sure you know, the J/B is more than simply a fuse box, being a computer having an internal circuit board and external plug-in relays, etc. My local dealer was stumped too and had to contact Japan for help. This is a very rare problem indeed.

MrMaxP0WR

Jin3198 - Did your gauges brightness still change with the dimmer while your dash lights were out?

Tom57 - Can you elaborate on J/B? What is the full part name or number?

After a few hours of research on this odd problem, I'm stumped. My dash lights do not work, climate control stays in "day mode", while the gauges continue to be adjustable using the dimmer. I've tried full click "ON" and "OFF" with no changes to dash lighting.

I appreciate any info you can share!

Tom57

I replaced the driver's side junction block (J/B). The J/B is more than just a fuse box; it's a computerized electronic relay.

What year is your LS? Here is an example of the J/B for '01 - '03: http://www.ebay.com/itm/OEM-01-03-LEXUS-LS430-DRIVER-LEFT-SIDE-UNDER-DASH-JUNCTION-FUSE-BOX-82730-50080-/251798812318?hash=item3aa060f69e&vxp=mtr
Your symptoms do sound similar to mine. The J/B is fairly easy to DIY replace. The emergency brake pedal arm in front of the J/B is tricky to work around.

MrMaxP0WR

Thanks for the great info! Oddly enough, the day after I posted this, the lights are back to normal.

I think I'll purchase the item suggested just to keep as a spare.

Thanks again!

Tom57

Yes, that's how my center console lights and Nav screen would act too - intermittent - fine then abnormal bright Nav screen at night. But then steadily got to be more often bright (day mode) at night on Nav screen, and console lights dark. Note too that it could be the rheostat (rotary light dimmer) as Jin3198 experienced. As you can see from my prior posts on the thread, that is what I thought my problem was too. I checked with my Lexus Parts Manager back then and he said the dimmer was highly unlikely and noted there were only a few of them available in the U.S. (rarely replaced). But the dimmer is only $100 and is easily replaced too, even easier than the driver's side J/B. There is a fuse in the Driver's side J/B that is related to the console lights as well. The driver's side J/B, light dimmer and light sensor (little round button on the top of the dash under the windshield) all work together to manage the dash and Nav screen light settings.

CBSSYS

When mine acts up (about 50% of the time), dash and cnsole lights go out when screen goes full bright. I live close to McGrath Lexus downtown and they got me the dash lights dimmer switch quickly. Did not help though.

Jim in Chicago

Tom57

Jim, those are exactly the symptoms I had. When I was diagnosing, I thought it might be the dimmer switch too - but I didn't change it because it is not common for that switch to fail (McGrath Lexus told me there were only a couple dimmer switches in the Lexus parts system in the entire country.)

You need a driver's side Junction Box. Get one off eBay and replace it yourself.

There are two different part numbers and two different prices showing for 2004:

(1) 82730-50120 > http://www.lexussouthatlantaparts.co...273050120.html
(2) 82730-50081 or 82730-50080 > http://www.lexussouthatlantaparts.co...273050081.html

Ask McGrath what junction block part number you need - if the 82730-50080 will work. (They charged you for a dimmer that didn't fix the problem.) It is possible that one of the relays on the junction block has failed, but it's hard to know which one - even the dealer would sell you a whole new block, not just a relay that plugs into the block.

Tom57

Further research shows the correct driver's side J/B part # for 2004 - 06 is 82730-50120.

Here are two recycled driver's side J/Bs for 2004:

http://www.ebay.com/itm/2004-2005-2006-Lexus-LS-430-Left-Side-Fuse-Junction-Box-Relay-82730-50120-Cheap/252289779423?_trksid=p2047675.c100011.m1850&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D1%26asc%3D35694%26meid%3Daf0da76233074ea09fd2a83a13cd4985%26pid%3D100011%26rk%3D1%26rkt%3D2%26sd%3D271952984194

http://www.ebay.com/itm/2004-2006-Le...hUbkz9&vxp=mtr

CBSSYS

Tom, it sounds like you really have this one nailed. I was able to really examine this part that was for an '03. It had LOTS of plugs and looks very complex. Hope they check out the used ones because that is the way for us to go. We love this car and it just hit 225k miles. Its only other issue I will post later today and soon the car will be perfect!!

Jim in Chicago!

Tom57

Jim, used is the only way to go on this part. There are relays plugged into this J/B that cost almost as much as the entire J/B used. Then, there are internal resistors etc. on a circuit board inside the J/B that are not user-serviceable, and not worth it even if you want to test each part. McGrath Lexus will use LKQ recycled parts if you ask, or source a driver's side J/B yourself and have them install it if you're not inclined. Good luck.