Hey, folks, I just bought a 2004 SC430 with about 220k. I test drove it and all of the essential systems worked well.
After I got it home (yeah, make sure it all works before buying it), turns out a bunch of peripheral systems aren't working. Windshield washers, power mirrors, TPMS, instrument panel lighting, door locks and undoubtedly more. Is there a common fuse or relay failure that typically does that? I got out of diagnosing such things for a living in 1999, so I don't really have a clue any more. I'm hoping it's not a control module.

Edit, I made my living diagnosing such things until 1999, but it's all moved on. I'm way out of touch.

 

Welcome to the Club and Congrats on your first post !!

I can’t help you with most of your post — all I can offer is to go to your local dealership, a reputable Japanese specialty mechanic or a Toyota dealership might be able to help you.

The TPMS sensors don’t show individual tire psi so as long as you manually check and know psi is good on all tires, you’re good. Some owners have installed systems that show individual tire psi so that’s an option. The TPMS sensors are color coded for 2002-Jul 2006 SCs. They run on batteries that can’t be replaced, you have to buy a whole new sensor. Our red one is out and we live with the light on, or sometimes it goes off. As long as we know our PSIs are good then we’re okay with the light. As far as I know there are no good aftermarket replacements for the OEM ones.

Part numbers for SC430 TPMS sensors: 2002-July 2006

42607-24041 Gold
42607-24031 Red
42607-24011 White
42607-24021 Blue

They’re on sale now thru Dec 3rd with Free Shipping and No Sales Tax for out-of-state customers. Here are three links to dealership Parts Depts for the Gold TPMS Sensor in FL, AZ, and NJ, depending on where you live, with FL and NJ being cheaper.

Good luck with everything else and update this thread to let others know what the cause was and how you resolved your issues.

4260724041 - Lexus Tire Pressure Monitoring System (TPMS) | Treasure Coast Lexus, Ft. Pierce FL

4260724041 - Lexus Tire Pressure Monitoring System (TPMS) | Bell Lexus North Scottsdale, Scottsdale AZ

4260724041 - Lexus Tire Pressure Monitoring System (TPMS) | Prestige Lexus, Ramsey NJ

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EDIT: I forgot to mention the instrument cluster lighting is a known issue for being very dim — here is a fix for that done by SC430mods.com

Instrument cluster BRIGHT LED upgrade (5 speed automatic only) | SC430Mods

 

Get Techstream software and OBD2 connector installed on a laptop. It is the system toyota/lexus dealers used. In your case, I think it will be well worth it to help track down your problems. The software and connector are on ebay for less then $50. Something like this. This one ships from china. Shop around, you might find one more local that arrives sooner.

Where are you located ? There might be a forum member in your area who has it and would be willing to help.

Good luck.

 

OP - symptoms sound a lot like a fuse or relay issue. I just resolved something like this on one of my non Toyota/Lexus cars with good results - my case fuse was fine relay was bad and it turned out to be a $15 fix to replace the relay with used OEM parts. If you have a test pen, open up the fuse box in the engine bay as well as the one in the footwell and start testing fuses one by one. You have so many things out it could be multiple fuses. If the fuses check out then a google search for relay maps and what relay controls which system will get you more than half of where you need to go. Once you isolate the relays that could be a problem, activate the relevant system in the car and have someone stand by the relay box to listen for the relay to click. If it clicks at least you know part of the relay is working ( but not necessarily all of the relay ). If it does not click then you know for sure the relay is not working. Search for a replacement relay and swap out. I think some OEM's recommend disconnecting the battery before pulling relays - not sure what the status is with Lexus. My SC's electrical has been bulletproof so I am lucky there. Last suggestion - worth checking strength of your 12v battery. Strange and random things happen when the battery is old. Just cos it allows you to start does not mean it can power all the rest of the electrically actuated stuff.

I assume TPMS means your light is lit up. If you want to go the OEM route - @RofH has the answer for you up there. It is not cheap so get ready for sticker shock. I went the aftermarket route and could not be happier - real time tire pressure and temperature read out for each tire on a small solar powered display - like a modern car. Schrader makes that system.

 

Yea,

Check your battery before jumping in head first.

In retrospect, when my battery was dieing, the car behaved a bit oddly. Nothing I could put my finger on, just not right.

Good luck.

 

Thanks. I have a Toyota/Lexus-specific Launch scan tool that's been surprisingly good for the price, with access to a whole bunch of systems. Life and weather have kept me from digging into the problem with the scanner yet. I hope to get it inside the garage within a few days, and will see how much information it can pull. If it's not adequate, I'll go to Techstream.

 

Fuses and relays were my first thought, and I have quickly checked a few fuses, but ran out of time to go further. The battery is both new and good. The TPMS problem is that the light does not come on even with the pressure being 7psi low, and I haven't noticed it on the instrument cluster ignition-on test cycle. I suspect there is at least one control module that either isn't getting powered up or has failed, affecting a bunch of networked systems.

FWIW, I'm a retired ASE Master Auto Technician, and I spent much of my 20-year automotive career focusing on driveability and electrical problems. I got out of that line of work in 1999, so I have nearly zero experience with networked systems, particularly Canbus. I've dipped my toes in the subject a little bit, but I don't have much specific knowledge of pattern failures, etc.

I have aftermarket TPMS on my motorcycle, and it works fine. I think it's very likely that the TPMS problem is tied in with the other inoperative systems. I hope to get enough stuff out of the garage tomorrow to fit the SC in, and let it warm up a bit.

 

Sounds to me like maybe your TPMS might have been disabled, which people do when they don't want to see the light, or hear the screech it makes.

Look on this Forum's Main Page under the "Sticky Threads" -- "How to Disable (TPM) System".

This is a very L - o - n - g Thread, but maybe you can do the reverse and re-enable the TPMS.

See Post #13 , pictures on #20 and Post #25 -- there could be others and hope this might help.

 

Does anything else not work?

The SC has a multiplexer, it takes care of all of these functions

The SC430 multiplexer module manages communication between various electronic components in the vehicle, such as doors, lights, and other systems, allowing them to work together efficiently. It helps control functions like door locking, window operation, and lighting.

Overview of the SC430 Multiplexer Module

The SC430 multiplexer module is an essential component in the Lexus SC430 vehicle. It manages various electronic functions and communications within the car's network.

Functions of the Multiplexer Module

Communication Management

• Data Transmission: The multiplexer module facilitates communication between different electronic control units (ECUs) in the vehicle.
• Signal Processing: It processes signals from various sensors and modules, ensuring they work together seamlessly.

Control Functions

• Door Operations: It controls the operation of the vehicle's doors, including locking and unlocking mechanisms.
• Lighting Control: The module manages the front and rear lighting systems, ensuring proper functionality and safety.

Additional Features

• Comfort Features: It may also control features like seat adjustments and climate control settings.
• Security Systems: The module plays a role in the vehicle's security systems, including the theft warning system.

Importance of the Multiplexer Module

The multiplexer module is crucial for the overall functionality and safety of the Lexus SC430. It ensures that various systems communicate effectively, enhancing the driving experience and vehicle performance.

lexuspartsnow.com biggsmotoring.com

 

Thanks for that info. A number of things don't work. Off the top of my head, dash lights (totally dead, not just dim), windshield washers, remote fobs (batteries tested good), possibly Homelink, probably some others. Multiplexer sounds like a possibility. At least it's not crazy expensive.

It's supposed to be 21 degrees tonight, so I managed to get the car into the heated garage. Yay! I plan to devote as much of the day as needed to diagnosing this stuff. Right now it's time to entertain the dog and relax.

 

I did get the car into the garage and verified that all of the fuses are good and powered up. I ran a second system scan, and got a B1261, which indicates a loss of communication with the ECM. along with a B1421 and a B142 , sunload sensors, driver and passenger side. I'm skeptical about the latter two. Googling indicates that those two get set if you run a code scan while the vehicle is inaide without direct sunlight. Based on several threads here and there, I have disconnected the battery cables and jumpered them together to drain any capacitors that may still have held a charge.I have run into that procedure in factory service manuals over the years, so it's apparently legit in some cases. I gotta sleep anyway, so tomorrow we'll see if it had any effect. What's the worst that can happen?

 

You’d be surprised how many people didn’t think to push the button on the end of stalk for the windshield washer

We — yes, me included, just assumed to pull stalk towards us to make it squirt washer fluid.

Yes, we finally figured it out, but took us a minute…

 

D'oh! Considering how often I suggest that people RTFM, this could be embarrassing...

 

So I went to the garage, reconnected the battery and scan tool, and fired her up. The dash lights worked (They don't dim, but that's not really a problem.) The CD changer decided it wasn't jammed after all, and Carlos Santana started playing Soul Survivor. I found the little button on the stalk, and the windshield washers do work. The scan tool didn't find any codes. I didn't want to make more noise, so I didn't try the door locks, but I expect they will work. I didn't see a TPMS light on the dash at startup, so I guess that has been disabled, or maybe this car wasn't equipped with it. I'll dig into that later. I have tire pressure gauges.

So I'm going to call it an all-around win. Thanks for all of the suggestions!

Now to fix the noisy serpentine belt tensioner and idler...

Edit: I disconnected the battery and drained capacitors again,. This time I cranked up the engine immediately after reconnecting the battery, and the dash lights will go from dim to dimmer (Dash lighting by Lucas?). I think they will be fine for me.

 

Great results congratulations. Welcome to the community. Hope you can help us all with your experience. Amazing to me how these old SCs keep going. I walked away from my 20 year old SC this morning in the office parking lot after a 31 degree commute over 65 miles and she was even smoother on the roads in the cold than when it's 80 degrees out. My ASE certified indy mechanic says they don't make em like this no more. Believe the ASE certified guy right ?