Hey so I just bought this 2000 Lexus gs 300 and test drove it for like 2 hours no problems nor check engine light. I park it over night and drive it in the morning and then cel is on and its shifting hard 1st and second gear. After driving for about 30 minutes it starts shifting good. My question is will I be OK replacing the selenoid and then filter and fluid? Or do I have to replace the transmission? Also can I replace the selenoid myself if so how?

 

check your transmission fluid.

first step is drain and replace all fluid - easy enough to do, couple of pipes under engine, disconnect them, then turn engine over to pump old fluid out.
drain/remove sump, clean filter.

that *might* be enough, without replacing solenoid.

link to "how-to" in this thread

 

Is it OK if I just go get it flushed? Will it hurt it will 115000 miles? I did the drain and refill yesterday by draining pan and refilling through dipstick. I did this procedure 3 times. What two pipes are you talking about and how much fluid will come out if I do it that way?

 

do NOT flush, do NOT flush. The only PROPER way for this car to change the tranny fluid WITHOUT hurting it is to do a drain and refill. Simply drain out the old fluid until its empty and pour new fluid in. Do this about 5 times or as many as possbile to ensure all the old fluid is out but make sure you do alot of driving between drain and refills and this might help. If that doesnt work, do it one more time but change the solenoid at the same time and you should be good. My girl had a 98 GS4 that had this same problem, hard shifting and a CEL and we changed the solenoid and it went away but changing the fluid a couple times helped it shift much better but we still needed to change the solenoid eventually. Might as well try that first.

 

Hey I did exactly What you said and it didn't work so I changed the solenoid and the code went away BUT it still shifts very hard 1st gear when the car is cold for like the first 15 min and then it goes away... the only cel code I have now is a p0446 code. What could cause my transmission to do this still do Ineed t III go to Lexus and get computer reset?

 

Don't ever go to LEXUS for anything except to purchase the parts. Find yourself a good indy mechanic that knows a lot about lexus. You must go to autozone to have your CEL reset and drive for 100 miles and see if it comes back. The hard shifting should have went away from changing the solenoid and draining and refilling the fluid. You need to drain and refill over the course of a year, driving it as much as you can and change it every 2-3 months.