Toyota proper is essentially silent on when you should change the fluid in automatic transmissions under ordinary driving conditions.

They merely convey to examine and advise. We suggest changing your automatic transmission fluid by way of flushing it as being preventative maintenance every 30,000 miles, or sooner in the event the fluid has gone through a substantial colour change that signifies its condition has started to degrade.

The existing fluid can not be efficiently removed by merely draining. Because of the torque converter not draining, the majority of the fluid remains within the system whether or not the pan is removed.
The best way to accomplish a complete changeover from the transmission fluid would be to flush the entire system. This is very important to the life and health of your vehicle, and much more economic than being required to shell out the thousands required replacing or rebuilding your transmission later on.

The question is from time to time raised whether changing or flushing the transmission can cause any problems, especially when it comes to a vehicle that’s long overdue for the fluid change. In more than 16 years of performing this particular service I haven’t known any damaging consequence which may remotely be perceived as a result of changing the transmission fluid. I do not remember even any transmission incident that may have been perceived as a regrettable coincidence after changing the material. The approach we take to flush the transmission is actually nothing more than a incredibly thorough fluid change. After draining the pan, we make use of the transmission’s own pump to pull in new fluid and push it through the system in the normal direction of flow, pushing out the old fluid ahead of the new. New fluid is pumped through the torque converter and on out from the cooler where we capture it within a drain pan. What could possibly be a more natural or safe way to change your transmission fluid?

Some shops use machines in the flushing procedure that might bring in other issues in to the process compared to what I have described as our procedure. A few of these issues may include special solvents and elevated pressures. Although I hear folks discuss back-flushing, I am not aware of whether any one of the standard procedures essentially involve reversing the fluid flow. I can not say from general observations regardless of whether these alternative procedures raise the potential risk of creating an unintended issue or not.

Signs your vehicle requires a transmission flush: Transmission Grinding or Unusual Sounds, Surging of the Vehicle, Slipping Gears, Trouble Shifting Gears.