Is O'D supposed to be on or off?

The O/D off button allows you to prevent an automatic transmission from shifting into those top gears in certain situations, such as when driving through rolling hills, going down steep grades and hauling a heavy load or trailer. For best fuel economy under normal driving conditions, you want to remember to hit the O/D off button again in order to allow the use of the overdrive gears. This can be advantageous for acceleration, even on fairly level ground when carrying heavy loads or towing a trailer. Later automatic transmissions with five or more speeds may have more than one overdrive gear ratio, so hitting the O/D off button may lock out more than just the very top gear. The transmission would have to shift down to 3rd gear to get up the hill, then would shift back to 4th going downhill, then back to 3rd to get up the next hill. As a result, some automakers have added the O/D off button to allow the driver to lock out 4th gear and hold the transmission in 3rd.

Overdrive is usually on by default, and when it's off, your car’s transmission will automatically utilize the highest gears if you get up to a high speed. The O/D Off light indicates that the Overdrive function is disabled. Find the button on the gearshift and press it to turn O/D back on. Overdrive is usually on by default. It prevents your vehicle from using the highest gears to help with engine performance, increase fuel economy, and make driving at high speeds easier. When overdrive is active, your transmission is not allowed to move into the highest gears. Realistically, it’s going to be rare that turning Overdrive off is really beneficial. Most of the time, restricting your transmission to the lower gears will just save you gas money. If you’re not driving under some unique circumstances, there’s no good reason to shut the feature off.

When the overdrive gets turned off, the car will not allow the transmission to operate in the highest gear but limits it to a lower gear to increase friction to ensure safety and save fuel. The o/d off button allows you to prevent an automatic message from shifting into those top gears in certain situations, such as when driving through rough hills, going down steep terrain, and hauling a heavy load or trailer. Although the overdrive function gets used when driving in rough terrains, the overdrive should get turned off in such a situation. Note that when the indicator light is on, the o/d is off, and when the light is off, this means the overdrive feature is on. When shifting to a lower gear, turn the overdrive feature off. As a driver when there is no need to accelerate, the overdrive function should be turned off. Also, when driving up a hill or downhill, the overdrive function may lose its effectiveness. If the overdrive indicator light flashes, the o/d function has to get disabled. Before enabling or disabling overdrive, you should carefully identify the situations in which you might use it. This switch will stay open by default unless turned off. Simply put, when the default o/d function is OFF (the indicator light is on the dashboard), all gears in the transmission are in use. Still, when the indicator light is off, this means your vehicle is setting the overdrive On state to allow you to accelerate over the limit again.