OK to fix this code p0768 is really easy is gonna be part #35230 solenoid s4 check ohm from ground to + on solenoid should be 10 to 14 ohms. If you get nothing Change it out with a new one. You can check this on transmission terminal plug located under battery bracket, remove air intake filter resevoir and battery to get to plug or take it out from under trans and then check it . You can also put 12 volts to it and hear it open and close. You can do this yourself or you can pay to get it done. Took me like an hour to do. make sure to use a cork gasket with blue locktight on bolts, not that black rubber buna crap gasket that the auto part store sells you.,"it leaks". I got my stuff at a trans. warehouse by the house , filter and gasket cost $25 and solenoid 35230 was $90 with tax. Trans oil syntec. got it at walmart for $17 the gallon. Took 1 gallon to refill and 1 to flush old stuff and one mor to top it off to dip stick mark. Remeber to fill to top cold indicator line then let it run change gear and drive it gently to oil warms up then check again should be at top hot line indicator. If not top off till it is. Or take a trip to pick a part and find a toyota 99 to 04 and take it from there, is gonna be the one with the black plug. That should fix p0768, did for me. My rx300 has 240000 miles and runs like new now. I change trans oil and filter every 50k and motor oil every 3 to 4 k.
