Here's how to change the automatic transmission fluid in a Toyota or Lexus with no dipstick.

Toyota claims the transmission in its modern cars is a sealed unit, and the fluid inside is good for the lifetime of the vehicle. However, transmission fluid does wear out overtime, and if you want to prolong the life of your transmission, its a good idea to change the fluid frequently.

This procedure is the same for most recent model Toyota and Lexus RWD and 4WD vehicles, including Lexus IS250, IS350, GS350, LS460, GX460, Toyota 4Runner, Tacoma, Tundra and Sequoia. This procedure is similar to recent models Lexus and Toyota FWD and AWD models, with the exception that the transmission is mounted transversely, including the Lexus ES350, RX350, Toyota Avalon, Camry, Highlander, Sienna and Venza.

Here's a full DIY Write-up on the fluid change procedure for reference:
http://www.clublexus.com/forums/gs-3rd-gen-2006-2011/736105-changing-transmission-fluid-diy-w-pics.html

Its also a good idea to drop the pan and replace the filter, here's a write-up on that:

http://www.clublexus.com/forums/gs-3rd-gen-2006-2011/838073-changing-transmission-filter-strainer-diy-w-pics.html

Step 1: There's No Dipstick...

Under the hood you'll find....nothing. These newer tranny's don't even have a dipstick to check the level. Toyota really doesn't want you playing with the transmission.

Well next you'll have to jack it up (with the vehicle level) and have a look underneath.

Step 2: Underneath the Vehicle

Remove the six 10mm bolts and nuts that hold the plastic cover under neath the transmission pan.

This will expose a 14mm drain bolt, and a 5mm hex overflow bolt.

Step 3: Drain the Fluid

Open the 14mm bolt and let all the fluid drain into a catch can.

Notice how red the fluid is...that's a good thing. Worn fluid will be brown and really bad fluid will be black.

Measure the amount of fluid that came out...this is exactly the amount you must replace into the tranny.

Step 4: Transmission Fill Port

Remove the two 10mm bolts on the driver's side of the transmission. The plastic cover can then be removed to access the 24mm WS fill bolt. Remove the fill bolt.

Use only Toyota WS automatic transmission fluid.

Step 5: Pump Fluid Into the Transmission

A fluid pump must be used to pump ATF into the transmission from below.

Put the inlet hose of the pump into the transmission fluid bottle, and the outlet securely into the fill port of the transmission.

Pump the exact amount of fluid that came out of the transmission into the transmission. If you will be performing the following fluid check procedure, add 1/4 quart extra fluid to make sure you get the level just right.

Step 6: Measure the Temperature of the Transmission

Instead of a dipstick, sealed transmissions have an overflow bolt that's removed when the transmission is at a specific temperature, in this case, 104F. Above the overflow bolt is a straw which determines the level of the fluid when the temperature is correct. Excess fluid will flow through the straw and drain once you remove the bolt.

To measure the transmission fluid without expensive scan tools, short pins 4 and 13 on the OBDII port under the dash. Turn the vehicle on, this will put it in diagnostic mode, with a higher than normal idle, and lots of scary lights flashing on the dashboard.

Shift the transmission into S, go from first to sixth gear, then back to P. Then put it back into D and oscillate quickly between N and D for at least 6 seconds. Then go back to P. This will put it in fluid temperature detection mode. When the P and D lights are both lit green, the fluid is at the optimal temperature for checking its level.

You can also use Toyota's own techstream software paired with a MVCI cable to determine ATF fluid temperature. More details on Toyota techstream here:

https://www.youtube.com/watch?v=KDpldAv0uQE

Step 7: Open Up the Overflow Bolt

With the engine running, open up the 5mm hex bolt on the bottom of the pan. This will let excess fluid drain.

Once the fluid drains to a trickle, tighten everything back up and double check for leaks. Replace the plastic under cover.

Step 8: Conclusion

Now that the transmission fluid has been changed, take the vehicle for a test drive and make sure all the gears shift smoothly. You can now enjoy smoother shifts, and peace of mind that your tranny will last much longer now that you've changed out the worn fluid.

Since this procedure only changes 2.5 quarts of the 12 quarts of total system fluid, its a good idea to perform this procedure 3-4 times with a few hundred kilometers of driving in between, to dilute the old fluid with fresh fluid.

Flushing the transmission through the cooler lines is not possible on this transmission type, since the transmission does not have separate lines running to the radiator. Flushing the transmission fluid is not recommended for a vehicle that does not have transmission problems, even if the fluid has never been changed, and should only be used as a last resort before rebuilding the transmission.
World Standard WS Toyota genuine transmission fluid should only be used and can be bought from the Toyota or Lexus dealership.