Just bought a 03 is300. Trans seems to be acting up. Going from 2nd to 3rd its hitting 5k. I checked the fluid and it was low. Added fluid and same thing. No check engine lights. I did just have to replace the bank 2 O2 sensor. When I place the car in manual mode shifts fine. Any suggestions??

 

Maybe the trans fluid being low/dirty caused damage that won't let the shift solenoids do what they're supposed to. Do you have any check engine lights?

 

I don't have a single light on now. I did have a code for the bank 2 o2 sensor but after I replaced it went off

 

Hmmm, you may check the codes anyway. The times my Lexus had issues with the trans the CEL was on.... every time there was some problem.

 

So have the codes scan again. I did have one but not sure if it was a stored code. It was still the p0435 bank 2. Would that cause shifting issues? I did buy some cat cleaner and sea foam. Cat cleaner is in. Plan on doing the sea foam tonight

 

I do not know what the proper factory procedure is for testing o2 sensors but I would imagine it has something to do with watching what their signal does over time. Mine that were bad had very small oscillation trending to one end of the range and another was stuck completely at one extreme (complete lean I think). Replacing the bad sensors AFTER determining that they were bad fixed the issues with the transmission for me.