For 2007 Gs350
In the automatic transmission oil level check
I want to know what purpose sst 09843-18040 tool is used for.
I don't think it's just an oil temperature check, but is it for TCU reset?
Does anyone know exactly?

 

It looks like that part number is for a "jumper wire", which allows you to tell the ECU to enter diagnostic mode. After a certain series of shifting the car into drive and park (I think?), the dash board shift indicator will change to show if the fluid is below checking temperature, in the temperature interval where the level check is specified, or over the level check interval. Kind of a pain, so if you have access to Techstream, probably better / easier to do that.

Here's a YouTube video that explains the whole fluid change process, including entering the fluid temperature check mode (at about 4:42 in the video):


Note that AWD models are slightly different -- there isn't a plastic belly pan below the transmission, nor is there a cover over the fill bolt.

 

Oh, so the purpose of the jumper wire is nothing more than a temperature indicator.

Thanks for the comment.