Hi everyone I am writing this because I get asked alot on the streets about my RX300 trans. It seems like everyone who has a RX has this problem with their trans one time or another. What the trans does it will have an erratic shift or a hard down shift shudder or it just goes nuts then breaks down for no reason that what people think they break for no reason. To solve the big mysterie if its not been solve yet, well to those of you trying to save your transmissions and doing tons of trans services and flushes hope this helps. From my own research and experiences and inside scope of all that is Toyota/Lexus from Toyota engineer insider. Giving it to u straight forward it not always the trans thats giving out meaning it not just a mechanical failure, but a software firmware issue. The software or Toyota trans logic they call it on vehicles RX300s, the ecu can sometime find the right throttle position and sometimes can not when it can not find the right throttle position or "load" it does not no what to do so it tend to give the wrong command to the wrong solenoid which in turns create erratic shifts. If this problem exists for long periods of time it damages the internal part this which causes lots of metal shaving or trans heating from worn parts. The ecu is what killing your trans, but what plays a major role is maintenance of the throttle body plates and maf sensor, keep them clean if you have erratic shifts acurring. Shift command by the ecm only happens if the ecm knows the engine load. Some people dont even notice bad shifting they just notice the car is slow or it takes time to upshift "delay" we call it. In conclusion the RX300 model or even other model have bad trans logic problems. There are ways to comfirm this. Remember the trans is mechanical.

 

+the other issue is the Planetary gears which had a aluminum carrier on the early models. Bad design by nature with such a heavy vehicle. Many shops put in a stronger steel carrier with an additional support gear.

 

The main issue is with the programming, Toyota was aiming for a 10% gain in FE. This compromised the durability of the transmission. I went a bit more in-depth a few months ago.

 

Can you post a link? I'd like to read your analysis.
Thanks.

 

There's another post somewhere here where I wrote a bit more, but I can't find it at the moment.
https://www.clublexus.com/forums/rx-...ml#post8192076
Post #5 in particular.

 

Thanks Hypervish,

I read your post and found it very interesting. I have a code reader that will let me monitor the transmission gear selected as I drive. Next time I take the car out I will try to observe the phenomenon you described.

I was also interested in your comments about DBW lag. Always wondered why my wife's 2004 ES330 did that. I think Lexus did offer a firmware upgrade to improve, but not eliminate, that problem.