I found this on the internet under mechanics, but you should only turn it on from park to 20mph.Before you go on the freeway.


Usage
Generally speaking, overdrive (OD) is the highest gear in the transmission. Most automatic transmissions have 3 speeds and overdrive (fourth speed). Overdrive allows the engine to operate at a lower rpm for a given road speed. This allows the vehicle to realize better fuel efficiency, and often quieter operation on the highway. When you switch it on, you allow the transmission to shift into overdrive mode after the certain speed is reached (usually 70+ km/h - 45+ mph) depending on the load). When it is off, the transmission shifting is limited to the lower gears. For normal driving conditions, operation of the overdrive should be enabled only if the average speed is above 70 km/h.
It may be necessary to switch it off if the vehicle is being operated in a mountainous area.
The automatic transmission automatically shifts from OD to 3rd gear when more load is present. When less load is present, it shifts back to OD. Under certain conditions, e.g: driving uphill or towing a trailer, the transmission may "hunt" between OD and 3rd gear, shifting back and forth. In this case, switching it off can help the transmission to 'decide'. It may also be advantageous to switch it off if engine braking is desired, for example, driving downhill. The vehicle's owner's manual has information and procedures regarding such situations..

 

Newbie here...just bought an '04 Accent. I'm a Lexus tech, been turning wrenches for 25+ years, which does NOT make me an expert. However, I use the O/D button alot, I use it to slow down and save on the brakes. Say I'm going 50-60, or even 70, and I see stopped or slowed traffic ahead I hit the button to take it out of overdrive...sure, at 70mph, the rpm's go up to 4000...but so what? The engine red lines at what...5-6000 rpm's. It's a nice ":slow-down" aid. Am I hurting the transmission? How and why? (it shouldn't, unless it's a crappy trans)

 

i always just left the OD button on when i had it in my sentra. i was told that when it was on it was pretty much enabling fourth gear, and to turn it off would be depriving the car of a higher gear.

 

Me too! I'd also like to know if it's going to hurt anything. I'm just use to downshifting in my '04 CompG with the paddle shifters.

-Jamie M.

 

Don't do that. You are using the trans to save the brakes. How much does it cost to replace the brakes? How much does it cost to replace the trans?

New brakes are cheaper than a new trans. Use the brakes to save the trans.

 

I winged it and have done it a few times, but never mid shift so don't know if thatd effect it or not

 

Just reading some of the older posts, I have a question.
How fast would you be going if you ran the RPM up to 4500 and were locked in second or third gear? Would you even do that?
Then why would you do that at 65-70 MPH? The trans ,condition unknown, may not be able to handle that too many times,
Just because you can do that or have done that many times doesn't make it right. Racing engines with hi volume oil pumps can handle this , but a std engine could be asking for trouble with such high RPMs. Ever see an engine with a hole in the side of the block , Spun bearing, oil starvation, connecting rod gets wings and flys out thru the block, not smart.