Solid first step with low cost assuming the ECU is the correct part # for the car.

 

Yes it’s the correct serial number for my car. I called up a local dealership to verify.

 

So, I got a call back from SIA, and they told me that the transmission side of the ECU needed repair after testing it, so it was the ECU all along (I am truly hoping).

This is what the tech told the lady I spoke with. If they don’t find any issues with the ECU they will tell you right up front and only charge $80 and ship the ECU back to you.

I should receive the ECU hopefully by the end of next week and see if the problem is completely fixed now.

Got my fingers crossed! 🤞

 

Well it looks like the ECU repair didn’t work. The car ran ok for the first 10 mins, then the CEL came back on for the exact same code. 😩😞😢.

This confirms that I probably need a new trans rebuild now.

Not to mention, the car needs a new alternator since the battery keeps dying and is barely staying charged. I got it tested at Vato Zone, and their brand new shiny tester came back reading a faulty diode for my alternator.

I am having the worst of luck with this car. Should I sell it and recoup some of my money back, or should I get a rebuilt or a low mileage used transmission for under $2,000 and have a shop install it? I freaking love this car and how amazingly smooth they are to drive, but I’m at a crossroads at the moment and can’t afford to spend almost $4,000 for a full rebuild.

 

Read through the thread again. I did notice you mentioned refilling trans with fluid. Did you use something to refill to Lexus/Toyota spec by monitoring fluid temps and such? These trans are sensistive to proper fill levels.

A few other users have reported mixed results with SIA. Whike they worked for.mine and others, it is possible they didnt fix the issue. You have a couple choices here, send it back and have them relook at it or get a second opinion at another ecu fix place.

I would relook at both of these while looking for a used trans.

 

Here's what I did on my '06 ML with 107k when it was having rough downshift issues:
1. Had Toyota dealer replace shift solenoid valve from Belle Lexus,
2. In order to do this, they had to drop the pan. So they cleaned it and replaced 4 to 6 quarts of fluid with Toyota WS.
3. After these repairs, the rough shift was significantly reduced but still present.
4. Shipped the ECU to Relentless in suburban Dallas on a Monday.
5. Returned on Friday, reinstalled and everything was silky smooth. The pep that differentiates the 04-06 transmission from the earlier generation had returned.
About 4 to 5 weeks later, everything is still working beautifly . Very pleased. For what its worth both trusted Toyota, Lexus and independent shop said I needed a new transmission. They may be right, only time will tell. So far, all is very good. Hope this helps.

 

I appreciate the advice guys, but I think at this point, I’ve exhausted all of my options and will
most likely need a new trans.

The transmission shop that I took my car too, drained a tiny bit of excess fluid as it was slightly overfilled, so the fluid level isn’t the problem. They did a bunch of testing and couldn’t find a source to the code. Plus the previous owner also had an ECU shipped out for repair, which didn’t fix the issue.

SIA did say to get the ECU software updated as I called them and explained to them that I am still having the same transmission code. So sending It back is pointless at this time.

I had to order a new alternator, maybe the fact that the alternator has been bad this entire time, it could lead to shifting issues as the cars powertrain defaults to limp mode if not enough voltage is being sent properly to all of the vehicle electrical components? Who know, but regardless, the previous owner was a young girl that looked like she probably raced the car and drove it aggressively based on the wheels she had installed.

Because any person that would just drive these cars normally, shouldn’t wear out the transmission in these cars at 160k miles. Or maybe I am wrong?

But at the same time, I think it depends on where you live and how the road conditions are. She lived on a hill, and driving up that hill on a daily basis had to add additional stress and strain on the transmission.

I had a friend that lived on one of the steepest hills in San Diego, and most of his neighbors cars had transmission problems, and they all went through brake pads/rotors yearly. My friends truck had his transmission rebuilt twice, due to the extremely steep hill called “Dictionary Hill”. You literally have to “gun” the accelerator while driving up it because if you don’t, your car can stall out or strain badly trying to get to the top.

This is why I hate hills, and can’t stand driving on them. This causes all sorts of unnecessary wear and tear to ones vehicle. So to all of you that live on perfectly flat land, I envy you! 😂

 

Hard to evaluate if a trans should or should not wear out at 160k. Driving conditions vary and 160k mikes is a long time for someone to do something dumb like use the wrong fluid, wrong fill technique etc.

if you are remotely close to El Paso, i have a salvage title repaired LS430 2004. Trans works great. My daughter hit a deer with it and did enough damage that i am not fixing it. Uses a bit of oil but will drive anywhere. We still use it occasionally around town but one of the headlights is busted so we dont drive it often.

It can be bought cheap. I have a thread on here with our purchase and maintenance history. Trans should work if the years are interchangable.

 

I am facing the same, I bought my 2005 with 185 miles July 23 and everything was perfect. I had a couple of oxygen sensors issues but I sorted everything out getting all the codes on the dashboard removed. But this year on 2nd of January I decided to change the gear oil and I did, it was dark when it was replaced and I used 5 liters of wps OEM gear oil plus filter change and all. Unfortunately on 22nd of January. P0761 started to pop up and the gear shift stuck after 3rd gear when I drive the car in the morning as the rpm reaches 5000 with an 80 km/h of speed. Each time I park to solve the issue. I changed the s3 solenoid re inserted the oil to the appropriate pressure (I guess, I will talk about it in a minute). And the issue comes back especially when the car is cold. Right now the mechanic Is saying the clutches inside of the gear needs to be replaced as they have worn out (it maybe your case). I am not planning on doing so, as I think the oil change has to do with it. Regarding the oil level, the mechanic has drain the gear box, replacing the gasket seal and filter and when he put the oil back from the side of the gear box, he had filled it until it spilled out and then sealed the screws. I am not if this is the correct way as I think the oil level has got to do with my issue. I hope anyone has the correct way to level my gear oil correctly. And I wish you be able to solve it with the least cost possible. All the best my buddy in DTC 😅

 

This video may help you to know the detail.

 

Thank you, I am sure now my oil level is not accurate

 

Unfortunately, I live in CA, so that’s not an option for me. I say keep driving it if it runs and drives well.

 

I don’t think the fluid level is the problem, as another transmission shop also told me that the clutches inside the transmission has worn down due to lack of fluid changes and the previous owner driving the car very aggressively.

 

The trans fluid in the pan looks horrible and metallic. Magnet junk is normal, but fluid should be clear whether it's new and red or old and dark. Assume everything is contaminated at this point.

New trans, converter, probably radiator as well since all the fluid and metal is in there too. Spray out or flush the hard lines... If you only swap in a trans then all that contamination is going to ruin the new trans.

 

I have the hard downshift issue with my transmission 2nd to 1st gear in 04 LS430. I called the local dealer on a whim and they sell for $124 and available next day remanufactured ECU, with core. They need the specific number on ECU before ordering. This saves a little time and money instead of sending it out. If there are any issues, I'll report back. I have maintained ATF fluid changes every 60k miles ( now 271K) with Amsoil WS even though the first time I found out the hard way that universal ATF not always correct. Amsoil changed label after I reported my problem to them. No damage at that time and dealer flushed it out (at 60k miles then).

Thanks to all above posts, esp if this saves me from transmission rebuild. My goal is 300k miles and car runs perfectly otherwise, doesn't burn or leak oil.
Update: I decided to go with SIA electronics since they update software and give lifetime warranty. Took a week to get to it, but repaired whatever goes bad.
The hard shifting is gone and shifts better than new. Went from a paper weight back to new performance.