These threads explain how to run the in vehicle diagnostics that are available to the UZZ30, UZZ31 and UZZ32, many (if not most!) of the procedures and codes are also applicable to the Lexus SC400 and Lexus SC300. In some instances, the codes for the Lexus SC300 are also shown. (Although, they appear identical to the SC400 codes)
There are also diagnostic pages for the JZZ30 (twin turbo) BUT, unfortunately, they are in Japanese. (And Totally untranslated)
If you need to look up a diagnostic code for the TT, I suggest you first look up the SC400 codes. If the diagnostic code is not shown, please request information about the code on the forum. Someone who can read Japanese may well pop up and offer the translation.
The full technical documentation for the ALL Soarers is available on CD in the Soarer Bible and its companion CD, Soarer Wiring.