button is on the side/underside of the gearshift lever.

 

Its overdrive for the transmission,4th gear.
Just push button in on side of shifter and leave it on.
The older the rav gets the longer it takes for it to shift into overdrive when rav is cold.
The power button on dash keeps rav from shifting into next gear longer for more power and down shifts sooner but with button in power mode gas mileage suffers.

 

What does O/D Off mean, how come this light came on and how do I turn it off? I do not recall pressing any button that would have turned this light on and am not sure how to turn it off :roll: Would appreciate any ideas as to how to turn this off. Thanks

 

If AT, a little button on the side of the shifter, at least here in the U.S. for 2000. There's also a button on the center dash for something trans related too.

 

With the little button on the side of the shifter depressed (and so O/D light on), the A/T will be able to shift to fourth gear. With the button released, only three gears are available. Most of the time the button should be depressed (so all four gears are available).

This is in the owner's manual. See attachment.