I think you should replace the filter and renew as much fluid as possible (4 to 5 drains & fills should do it) so consumables and fluids are eliminated.

My transmission has been serviced by Lexus at 167k km, and it made it smoother. Not that it wasn't before, I said "rough" in my previous post but it wasn't really rough, the only thing was sometimes when I accelerated and braked a lot in a short period of time, I felt the shift just a bit, but it wasn't shaking the whole car either. Now, it doesn't happen anymore. The transmission is buttery smooth and gear changes are quick.

I can even say that I think Aisin RWD transmissions are the best in class ex-aequo with ZF transmissions (a bit quicker but less reliable). Shift points are perfectly calibrated.

Now, regarding the downshift issue caused by the ECU, I don't know when it will happen and what are the probabilities. At least we are lucky that a company such as SIA exists so we can have it repaired without breaking the bank.

 

Thanks, I'll look up a DIY on the filter change and see if I want to do that too.

 

I'm having thay same problem. My gs 300 won't shift into over drive kn freeways. Any one have a idea why ?

 

I'm having thay same problem. My gs 300 won't shift into over drive kn freeways. Any one have a idea why ?

 

I wish I knew but sounds like you need a new trans maybe just sell the car and look for a 350?

 

Have you sent out the ecu to SIA electronics to have them inspect the transmission module thats inside the ecu? If not park the car and remove the ecu and mail it out to them. They are quick turn around, they charge like $110-140 for the service and you can search on google or ebay. But this is a common problem on the 2006 GS300 only, they have ecu issues, but good thing SIA can fix them. If that doesnt fix it, then take it to a mechanic and have him test all the transmission solenoids as thats another common issue but not as common as the ecu.