Engine braking is the engine’s ability to slow the car when the transmission is in a low gear.

When you take your foot off the accelerator, decreasing the flow of fuel, the engine’s speed slows. Logically, the vehicle slows along with it, but the amount and rate of deceleration depends on what gear the transmission is in. The lower the gear, the greater the engine braking.

The concept of engine braking is much clearer to people who have driven with manual transmissions. Automatic transmissions tend to stay in their highest possible gears as the engine coasts or is braked to a stop, so the concept may not be familiar to folks who drive automatics. Drivers of automatic transmissions can take advantage of engine braking by shifting from 4 to 3 or lower on the gear selector of a four-speed transmission, or from 5 (or D5) to the next lower position with a five-speed automatic. On some vehicles, you achieve the same by turning off overdrive by means of a button, typically marked “O/D,” on the floor-mounted shifter or at the end of a steering-column-mounted gear selector lever.

The main reason you’d want to employ engine braking is to descend a steep hill. In such a situation, riding the brakes might overheat them and cause them to fade, possibly with disastrous consequences. That said, downshifting by too much for your current speed can be damaging or dangerous as well, so be sure to read your owner’s manual to find out the maximum speed at which you can run in lower gears or with overdrive turned off.

Information for this was taken from Cars.com’s glossary, written by Joe Wiesenfelder.

Answered by Joe Bruzek on June 26, 2008 in Glossary | Permalink

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