What Is the O/D Button in a Car?


Quick Answer

The O/D button switches the overdrive feature on and off. Only available in cars with automatic transmissions, overdrive determines whether or not the car engages the highest gear.

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Full Answer

When the driver presses the O/D button, the car actually turns off overdrive but lights up the O/D indicator. As such, when the O/D light is on, it indicates that the car locks out the highest gear. Because the highest gear produces less torque than the second-highest gear, it is a good idea to turn overdrive off when going uphill, overtaking another car or towing a heavy load. On the other hand, overdrive improves fuel economy and reduces engine wear.

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