Can I replace all the transmission fluid? or i need to mix the old with the new trans fluid? I'll never changed.
You can drain the old fluid out, about 3.2 qts comes out when you drain it, out of a total capacity of 8 qts. The rest of the fluid is in the torque converter. It is really simple to drain, just loosen and remove the tranny drain plug, and let the fluid come out.
I am not sure if changing the fluid will fix your problem, I do not think it could hurt at this point. I assuming the Toyota T-IV fluid was always used in your transmission. Fluid costs about $5-6 here in the northeast, I am not sure what you would pay in Puerto Rico. You never said if the fluid level was high or low, it must be checked when when the car runs for at least 15 minutes. If you answer all my other questions in my first reply, me or someone else might be able to help more. Does it shift abruptly or harshly and have you noticed any unusual noises? When you checked the fluid, was it foamy, and did it smell burnt? How many miles are on your car?
Do not ignore this code, you will probably need a new solenoid or torque converter since it is probably not locking up. I bet if you were to drop your tranny filter (which is more involved that just draining your fluid) there would be metal fragments in it.