[TrickyT]

Hey, nice install Adam. Great OEM look to it. And nice writeup too - very thorough.

Originally Posted by 96r50

...After some more time studying the EWD, FSM, and A343F manual I went and had a chat with the head Lexus mechanic (and good friend) at the local dealership. We concluded that the OEM ATF temperature sensor's only purpose is to set off the warning light on the dash when the fluid becomes (way, way, way!) too hot. It isn't tied into any other circuits according to any of the information we could find...

Probably true, but really hard to say for sure. As you know, the A343F is electronically controlled by the ECU. The FSM documents at least most, maybe all, of the sensors and switches that the ECU uses for input for controlling AT operation. Obvious things are throttle position, vehicle speed, and shifter position. The EWD mentions coolant temperature too, but doesn't say how it uses this input for AT control. The ATF temperaure sensor isn't mentioned. My point is that it's hard to know with certainty that the ECU doesn't also use ATF temp in some way too. For sure it uses it to turn the combination meter idiot light on/off, but it could consider ATF temp when deciding to lock/unlock the torque converter too, since that would be an obvious way to lower/raise ATF temperature.

Without looking at the computer program that runs in the ECU, we'll never know for sure. I think your conclusion about the ATF temp sensor only controlling the idiot light is reasonable, but you can't be 100% certain just because the Toyota manuals don't talk about it.