What does small OD button on gear shift do/mean?

On my 2002 Kia Sadona mini van I noticed about half way down a small button with the letters OD beside it. What does this mean and what does it do?

It allows you to turn “overdrive” off when you’re trying to pass another vehicle on the freeway, so the van will stay in 4th gear as you stomp on the gas, instead of upshifting to 5th gear.

It’s also helpful if you’re driving down a long hill to turn the OD off, which again prevents upshifting into 5th and allows the engine to help brake your descent, taking some of the load off the brakes.

Check the owners manual for vehicle specific operation but many situations require that overdrive be disabled. Trailer towing is the most common I believe. Some driving conditions can cause overdrive to be annoying, such as cruising at speeds between 45 and 50 mph when the transmission may repeatedly shift into and then immediately out of overdrive. pressing the OD button disables overdrive.

So basically since I just drive around town and don’t tow anything, i really don’t have a need to use it?

That’s correct. You have no reason to push the OD button.

Unles you wish to down-shift as you slow for lights and traffic.
Turning off the overdrive is downshift # 1.

Not So!!! If it is not in the o/D gear (like your not going fast enough), there will be no downshift. O/D off turns off the overdrive gear alone, and may reprogram the shift points a bit firmer on the other gears, which means it will shift a bit firmer. The transmission will continue to shift thru the gears before the overdrive gear.

This button is designed to prevent undo transmission damage when needing to put stress on the transmission, like when towing or driving up steep hills when carrying a heavy load. The owner’s manual will give you good guidelines when turning off the O/D would be advisable.